sudoers(5) File Formats Manual sudoers(5)
NAME
sudoers - default sudo security policy plugin
DESCRIPTION
The sudoers policy plugin determines a user's sudo privileges. It is the
default sudo policy plugin. The policy is driven by the
/opt/local/etc/sudoers file or, optionally, in LDAP. The policy format is
described in detail in the SUDOERS FILE FORMAT section. For information on
storing sudoers policy information in LDAP, see sudoers.ldap(5).
Configuring sudo.conf for sudoers
sudo consults the sudo.conf(5) file to determine which plugins to load. If
no sudo.conf(5) file is present, or if it contains no Plugin lines, sudoers
will be used for auditing, policy decisions and I/O logging. To explicitly
configure sudo.conf(5) to use the sudoers plugin, the following
configuration can be used.
Plugin sudoers_audit sudoers.so
Plugin sudoers_policy sudoers.so
Plugin sudoers_io sudoers.so
Starting with sudo 1.8.5, it is possible to specify optional arguments to
the sudoers plugin in the sudo.conf(5) file. Plugin arguments, if any,
should be listed after the path to the plugin (i.e., after sudoers.so).
The arguments are only effective for the plugin that opens (and parses) the
sudoers file.
For sudo version 1.9.1 and higher, this is the sudoers_audit plugin. For
older versions, it is the sudoers_policy plugin. Multiple arguments may be
specified, separated by white space. For example:
Plugin sudoers_audit sudoers.so sudoers_mode=0400 error_recovery=false
The following plugin arguments are supported:
error_recovery=bool
The error_recovery argument can be used to control whether sudoers
should attempt to recover from syntax errors in the sudoers file. If
set to true (the default), sudoers will try to recover from a syntax
error by discarding the portion of the line that contains the error
until the end of the line. A value of false will disable error
recovery. Prior to version 1.9.3, no error recovery was performed.
ldap_conf=pathname
The ldap_conf argument can be used to override the default path to
the ldap.conf file.
ldap_secret=pathname
The ldap_secret argument can be used to override the default path to
the ldap.secret file.
sudoers_file=pathname
The sudoers_file argument can be used to override the default path to
the sudoers file.
sudoers_uid=user-ID
The sudoers_uid argument can be used to override the default owner of
the sudoers file. It should be specified as a numeric user-ID.
sudoers_gid=group-ID
The sudoers_gid argument can be used to override the default group of
the sudoers file. It must be specified as a numeric group-ID (not a
group name).
sudoers_mode=mode
The sudoers_mode argument can be used to override the default file
mode for the sudoers file. It should be specified as an octal value.
For more information on configuring sudo.conf(5), refer to its manual.
User Authentication
The sudoers security policy requires that most users authenticate
themselves before they can use sudo. A password is not required if the
invoking user is root, if the target user is the same as the invoking user,
or if the policy has disabled authentication for the user or command.
Unlike su(1), when sudoers requires authentication, it validates the
invoking user's credentials, not the target user's (or root's) credentials.
This can be changed via the rootpw, targetpw and runaspw flags, described
later.
If a user who is not listed in the policy tries to run a command via sudo,
mail is sent to the proper authorities. The address used for such mail is
configurable via the mailto Defaults entry (described later) and defaults
to root.
No mail will be sent if an unauthorized user tries to run sudo with the -l
or -v option unless there is an authentication error and either the
mail_always or mail_badpass flags are enabled. This allows users to
determine for themselves whether or not they are allowed to use sudo. By
default, all attempts to run sudo (successful or not) are logged,
regardless of whether or not mail is sent.
If sudo is run by root and the SUDO_USER environment variable is set, the
sudoers policy will use this value to determine who the actual user is.
This can be used by a user to log commands through sudo even when a root
shell has been invoked. It also allows the -e option to remain useful even
when invoked via a sudo-run script or program. Note, however, that the
sudoers file lookup is still done for root, not the user specified by
SUDO_USER.
sudoers uses per-user time stamp files for credential caching. Once a user
has been authenticated, a record is written containing the user-ID that was
used to authenticate, the terminal session ID, the start time of the
session leader (or parent process) and a time stamp (using a monotonic
clock if one is available). The user may then use sudo without a password
for a short period of time (5 minutes unless overridden by the
timestamp_timeout option). By default, sudoers uses a separate record for
each terminal, which means that a user's login sessions are authenticated
separately. The timestamp_type option can be used to select the type of
time stamp record sudoers will use.
Logging
By default, sudoers logs both successful and unsuccessful attempts (as well
as errors). The log_allowed and log_denied flags can be used to control
this behavior. Messages can be logged to syslog(3), a log file, or both.
The default is to log to syslog(3) but this is configurable via the syslog
and logfile settings. See EVENT LOGGING for a description of the log file
format.
sudoers is also capable of running a command in a pseudo-terminal and
logging input and/or output. The standard input, standard output, and
standard error can be logged even when not associated with a terminal. For
more information about I/O logging, see the I/O LOGGING section.
Starting with version 1.9, the log_servers setting may be used to send
event and I/O log data to a remote server running sudo_logsrvd or another
service that implements the protocol described by sudo_logsrv.proto(5).
Command environment
Since environment variables can influence program behavior, sudoers
provides a means to restrict which variables from the user's environment
are inherited by the command to be run. There are two distinct ways
sudoers can deal with environment variables.
By default, the env_reset flag is enabled. This causes commands to be
executed with a new, minimal environment. On AIX (and Linux systems
without PAM), the environment is initialized with the contents of the
/etc/environment file. The HOME, MAIL, SHELL, LOGNAME and USER environment
variables are initialized based on the target user and the SUDO_* variables
are set based on the invoking user. Additional variables, such as DISPLAY,
PATH and TERM, are preserved from the invoking user's environment if
permitted by the env_check, or env_keep options. A few environment
variables are treated specially. If the PATH and TERM variables are not
preserved from the user's environment, they will be set to default values.
The LOGNAME and USER are handled as a single entity. If one of them is
preserved (or removed) from the user's environment, the other will be as
well. If LOGNAME and USER are to be preserved but only one of them is
present in the user's environment, the other will be set to the same value.
This avoids an inconsistent environment where one of the variables
describing the user name is set to the invoking user and one is set to the
target user. Environment variables with a value beginning with `()' are
removed unless both the name and value parts are matched by env_keep or
env_check, as they may be interpreted as functions by the bash shell.
Prior to version 1.8.11, such variables were always removed.
If, however, the env_reset flag is disabled, any variables not explicitly
denied by the env_check and env_delete options are allowed and their values
are inherited from the invoking process. Prior to version 1.8.21,
environment variables with a value beginning with `()' were always removed.
Beginning with version 1.8.21, a pattern in env_delete is used to match
bash shell functions instead. Since it is not possible to block all
potentially dangerous environment variables, use of the default env_reset
behavior is encouraged.
Environment variables specified by env_check, env_delete, or env_keep may
include one or more `*' characters which will match zero or more
characters. No other wildcard characters are supported.
By default, environment variables are matched by name. However, if the
pattern includes an equal sign (`='), both the variables name and value
must match. For example, a bash shell function could be matched as
follows:
env_keep += "BASH_FUNC_my_func%%=()*"
Without the `=()*' suffix, this would not match, as bash shell functions
are not preserved by default.
The complete list of environment variables that are preserved or removed,
as modified by global Defaults parameters in sudoers, is displayed when
sudo is run by root with the -V option. The list of environment variables
to remove varies based on the operating system sudo is running on.
Other sudoers options may influence the command environment, such as
always_set_home, secure_path, set_logname, and set_home.
On systems that support PAM where the pam_env module is enabled for sudo,
variables in the PAM environment may be merged in to the environment. If a
variable in the PAM environment is already present in the user's
environment, the value will only be overridden if the variable was not
preserved by sudoers. When env_reset is enabled, variables preserved from
the invoking user's environment by the env_keep list take precedence over
those in the PAM environment. When env_reset is disabled, variables
present the invoking user's environment take precedence over those in the
PAM environment unless they match a pattern in the env_delete list.
The dynamic linker on most operating systems will remove variables that can
control dynamic linking from the environment of set-user-ID executables,
including sudo. Depending on the operating system this may include _RLD*,
DYLD_*, LD_*, LDR_*, LIBPATH, SHLIB_PATH, and others. These type of
variables are removed from the environment before sudo even begins
execution and, as such, it is not possible for sudo to preserve them.
As a special case, if the -i option (initial login) is specified, sudoers
will initialize the environment regardless of the value of env_reset. The
DISPLAY, PATH and TERM variables remain unchanged; HOME, MAIL, SHELL, USER,
and LOGNAME are set based on the target user. On AIX (and Linux systems
without PAM), the contents of /etc/environment are also included. All
other environment variables are removed unless permitted by env_keep or
env_check, described above.
Finally, the restricted_env_file and env_file files are applied, if
present. The variables in restricted_env_file are applied first and are
subject to the same restrictions as the invoking user's environment, as
detailed above. The variables in env_file are applied last and are not
subject to these restrictions. In both cases, variables present in the
files will only be set to their specified values if they would not conflict
with an existing environment variable.
SUDOERS FILE FORMAT
The sudoers file is composed of two types of entries: aliases (basically
variables) and user specifications (which specify who may run what).
When multiple entries match for a user, they are applied in order. Where
there are multiple matches, the last match is used (which is not
necessarily the most specific match).
The sudoers file grammar will be described below in Extended Backus-Naur
Form (EBNF). Don't despair if you are unfamiliar with EBNF; it is fairly
simple, and the definitions below are annotated.
Resource limits
By default, sudoers uses the operating system's native method of setting
resource limits for the target user. On Linux systems, resource limits are
usually set by the pam_limits.so PAM module. On some BSD systems, the
/etc/login.conf file specifies resource limits for the user. On AIX
systems, resource limits are configured in the /etc/security/limits file.
If there is no system mechanism to set per-user resource limits, the
command will run with the same limits as the invoking user. The one
exception to this is the core dump file size, which is set by sudoers to 0
by default. Disabling core dumps by default makes it possible to avoid
potential security problems where the core file is treated as trusted
input.
Resource limits may also be set in the sudoers file itself, in which case
they override those set by the system. See the rlimit_as, rlimit_core,
rlimit_cpu, rlimit_data, rlimit_fsize, rlimit_locks, rlimit_memlock,
rlimit_nofile, rlimit_nproc, rlimit_rss, rlimit_stack options described
below. Resource limits in sudoers may be specified in one of the following
formats:
"value"
Both the soft and hard resource limits are set to the same value.
The special value "infinity" can be used to indicate that the value
is unlimited.
"soft,hard"
Two comma-separated values. The soft limit is set to the first
value and the hard limit is set to the second. Both values must
either be enclosed in a set of double quotes, or the comma must be
escaped with a backslash (`\'). The special value "infinity" may
be used in place of either value.
"default"
The default resource limit for the user will be used. This may be
a user-specific value (see above) or the value of the resource
limit when sudo was invoked for systems that don't support per-user
limits.
"user" The invoking user's resource limits will be preserved when running
the command.
For example, to restore the historic core dump file size behavior, a line
like the following may be used.
Defaults rlimit_core=default
Resource limits in sudoers are only supported by version 1.8.7 or higher.
Quick guide to EBNF
EBNF is a concise and exact way of describing the grammar of a language.
Each EBNF definition is made up of production rules. For example:
symbol ::= definition | alternate1 | alternate2 ...
Each production rule references others and thus makes up a grammar for the
language. EBNF also contains the following operators, which many readers
will recognize from regular expressions. Do not, however, confuse them
with "wildcard" characters, which have different meanings.
? Means that the preceding symbol (or group of symbols) is optional.
That is, it may appear once or not at all.
* Means that the preceding symbol (or group of symbols) may appear zero
or more times.
+ Means that the preceding symbol (or group of symbols) may appear one
or more times.
Parentheses may be used to group symbols together. For clarity, we will
use single quotes ('') to designate what is a verbatim character string (as
opposed to a symbol name).
Aliases
There are four kinds of aliases: User_Alias, Runas_Alias, Host_Alias and
Cmnd_Alias. Beginning with sudo 1.9.0, Cmd_Alias may be used in place of
Cmnd_Alias if desired.
Alias ::= 'User_Alias' User_Alias_Spec (':' User_Alias_Spec)* |
'Runas_Alias' Runas_Alias_Spec (':' Runas_Alias_Spec)* |
'Host_Alias' Host_Alias_Spec (':' Host_Alias_Spec)* |
'Cmnd_Alias' Cmnd_Alias_Spec (':' Cmnd_Alias_Spec)* |
'Cmd_Alias' Cmnd_Alias_Spec (':' Cmnd_Alias_Spec)*
User_Alias ::= NAME
User_Alias_Spec ::= User_Alias '=' User_List
Runas_Alias ::= NAME
Runas_Alias_Spec ::= Runas_Alias '=' Runas_List
Host_Alias ::= NAME
Host_Alias_Spec ::= Host_Alias '=' Host_List
Cmnd_Alias ::= NAME
Cmnd_Alias_Spec ::= Cmnd_Alias '=' Cmnd_List
NAME ::= [A-Z]([A-Z][0-9]_)*
Each alias definition is of the form
Alias_Type NAME = item1, item2, ...
where Alias_Type is one of User_Alias, Runas_Alias, Host_Alias, or
Cmnd_Alias. A NAME is a string of uppercase letters, numbers, and
underscore characters (`_'). A NAME must start with an uppercase letter.
It is possible to put several alias definitions of the same type on a
single line, joined by a colon (`:'). For example:
Alias_Type NAME = item1, item2, item3 : NAME = item4, item5
It is a syntax error to redefine an existing alias. It is possible to use
the same name for aliases of different types, but this is not recommended.
The definitions of what constitutes a valid alias member follow.
User_List ::= User |
User ',' User_List
User ::= '!'* user name |
'!'* #user-ID |
'!'* %group |
'!'* %#group-ID |
'!'* +netgroup |
'!'* %:nonunix_group |
'!'* %:#nonunix_gid |
'!'* User_Alias
A User_List is made up of one or more user names, user-IDs (prefixed with
`#'), system group names and IDs (prefixed with `%' and `%#' respectively),
netgroups (prefixed with `+'), non-Unix group names and IDs (prefixed with
`%:' and `%:#' respectively), and User_Aliases. Each list item may be
prefixed with zero or more `!' operators. An odd number of `!' operators
negate the value of the item; an even number just cancel each other out.
User netgroups are matched using the user and domain members only; the host
member is not used when matching.
A user name, user-ID, group, group-ID, netgroup, nonunix_group or
nonunix_gid may be enclosed in double quotes to avoid the need for escaping
special characters. Alternately, special characters may be specified in
escaped hex mode, e.g., \x20 for space. When using double quotes, any
prefix characters must be included inside the quotes.
The actual nonunix_group and nonunix_gid syntax depends on the underlying
group provider plugin. For instance, the QAS AD plugin supports the
following formats:
o Group in the same domain: "%:Group Name"
o Group in any domain: "%:Group Name@FULLY.QUALIFIED.DOMAIN"
o Group SID: "%:S-1-2-34-5678901234-5678901234-5678901234-567"
See GROUP PROVIDER PLUGINS for more information.
Quotes around group names are optional. Unquoted strings must use a
backslash (`\') to escape spaces and special characters. See Other special
characters and reserved words for a list of characters that need to be
escaped.
Runas_List ::= Runas_Member |
Runas_Member ',' Runas_List
Runas_Member ::= '!'* user name |
'!'* #user-ID |
'!'* %group |
'!'* %#group-ID |
'!'* %:nonunix_group |
'!'* %:#nonunix_gid |
'!'* +netgroup |
'!'* Runas_Alias |
'!'* ALL
A Runas_List is similar to a User_List except that instead of User_Aliases
it can contain Runas_Aliases. User names and groups are matched as
strings. In other words, two users (groups) with the same user (group) ID
are considered to be distinct. If you wish to match all user names with
the same user-ID (e.g., root and toor), you can use a user-ID instead of a
name (#0 in the example given). The user-ID or group-ID specified in a
Runas_Member need not be listed in the password or group database.
Host_List ::= Host |
Host ',' Host_List
Host ::= '!'* host name |
'!'* ip_addr |
'!'* network(/netmask)? |
'!'* +netgroup |
'!'* Host_Alias |
'!'* ALL
A Host_List is made up of one or more host names, IP addresses, network
numbers, netgroups (prefixed with `+'), and other aliases. Again, the
value of an item may be negated with the `!' operator. Host netgroups are
matched using the host (both qualified and unqualified) and domain members
only; the user member is not used when matching. If you specify a network
number without a netmask, sudo will query each of the local host's network
interfaces and, if the network number corresponds to one of the hosts's
network interfaces, will use the netmask of that interface. The netmask
may be specified either in standard IP address notation (e.g.,
255.255.255.0 or ffff:ffff:ffff:ffff::), or CIDR notation (number of bits,
e.g., 24 or 64). A host name may include shell-style wildcards (see the
Wildcards section below), but unless the hostname command on your machine
returns the fully qualified host name, you'll need to use the fqdn flag for
wildcards to be useful. sudo only inspects actual network interfaces; this
means that IP address 127.0.0.1 (localhost) will never match. Also, the
host name "localhost" will only match if that is the actual host name,
which is usually only the case for non-networked systems.
digest ::= [A-Fa-f0-9]+ |
[A-Za-z0-9\+/=]+
Digest_Spec ::= "sha224" ':' digest |
"sha256" ':' digest |
"sha384" ':' digest |
"sha512" ':' digest
Digest_List ::= Digest_Spec |
Digest_Spec ',' Digest_List
Cmnd_List ::= Cmnd |
Cmnd ',' Cmnd_List
command name ::= regex |
file name
command ::= command name |
command name args |
command name regex |
command name '""' |
ALL
Edit_Spec ::= "sudoedit" file name+ |
"sudoedit" regex |
"sudoedit"
List_Spec ::= "list"
Cmnd ::= Digest_List? '!'* command |
'!'* directory |
'!'* Edit_Spec |
'!'* List_Spec |
'!'* Cmnd_Alias
A Cmnd_List is a list of one or more commands, directories, or aliases. A
command is a fully qualified file name, which may include shell-style
wildcards (see the Wildcards section below), or a regular expression that
starts with `^' and ends with `$' (see the Regular expressions section
below). A directory is a fully qualified path name ending in a `/'. When
you specify a directory in a Cmnd_List, the user will be able to run any
file within that directory (but not in any sub-directories therein). If no
command line arguments are specified, the user may run the command with any
arguments they choose. Command line arguments can include wildcards or be
a regular expression that starts with `^' and ends with `$'. If the
command line arguments consist of `""', the command may only be run with no
arguments.
If a Cmnd has associated command line arguments, the arguments in the Cmnd
must match those given by the user on the command line. If the arguments
in a Cmnd begin with the `^' character, they will be interpreted as a
regular expression and matched accordingly. Otherwise, shell-style
wildcards are used when matching. Unless a regular expression is
specified, the following characters must be escaped with a `\' if they are
used in command arguments: `,', `:', `=', `\'. To prevent arguments in a
Cmnd that begin with a `^' character from being interpreted as a regular
expression, the `^' must be escaped with a `\'.
There are two commands built into sudo itself: "list" and "sudoedit".
Unlike other commands, these two must be specified in the sudoers file
without a leading path.
The "list" built-in can be used to permit a user to list another user's
privileges with sudo's -U option. For example, "sudo -l -U otheruser". A
user with the "list" privilege is able to list another user's privileges
even if they don't have permission to run commands as that user. By
default, only root or a user with the ability to run any command as either
root or the specified user on the current host may use the -U option. No
command line arguments may be specified with the "list" built-in.
The "sudoedit" built-in is used to permit a user to run sudo with the -e
option (or as sudoedit). It may take command line arguments just as a
normal command does. Unlike other commands, "sudoedit" is built into sudo
itself and must be specified in the sudoers file without a leading path.
If a leading path is present, for example /usr/bin/sudoedit, the path name
will be silently converted to "sudoedit". A fully-qualified path for
sudoedit is treated as an error by visudo.
A command may be preceded by a Digest_List, a comma-separated list of one
or more Digest_Spec entries. If a Digest_List is present, the command will
only match successfully if it can be verified using one of the SHA-2
digests in the list. Starting with version 1.9.0, the ALL reserved word
can be used in conjunction with a Digest_List. The following digest
formats are supported: sha224, sha256, sha384, and sha512. The string may
be specified in either hex or base64 format (base64 is more compact).
There are several utilities capable of generating SHA-2 digests in hex
format such as openssl, shasum, sha224sum, sha256sum, sha384sum, sha512sum.
For example, using openssl:
$ openssl dgst -sha224 /bin/ls
SHA224(/bin/ls)= 118187da8364d490b4a7debbf483004e8f3e053ec954309de2c41a25
It is also possible to use openssl to generate base64 output:
$ openssl dgst -binary -sha224 /bin/ls | openssl base64
EYGH2oNk1JC0p9679IMATo8+BT7JVDCd4sQaJQ==
Warning, if the user has write access to the command itself (directly or
via a sudo command), it may be possible for the user to replace the command
after the digest check has been performed but before the command is
executed. A similar race condition exists on systems that lack the
fexecve(2) system call when the directory in which the command is located
is writable by the user. See the description of the fdexec setting for
more information on how sudo executes commands that have an associated
digest.
Command digests are only supported by version 1.8.7 or higher.
Defaults
Certain configuration options may be changed from their default values at
run-time via one or more Default_Entry lines. These may affect all users
on any host, all users on a specific host, a specific user, a specific
command, or commands being run as a specific user. Per-command entries may
not include command line arguments. If you need to specify arguments,
define a Cmnd_Alias and reference that instead.
Default_Type ::= 'Defaults' |
'Defaults' '@' Host_List |
'Defaults' ':' User_List |
'Defaults' '!' Cmnd_List |
'Defaults' '>' Runas_List
Default_Entry ::= Default_Type Parameter_List
Parameter_List ::= Parameter |
Parameter ',' Parameter_List
Parameter ::= Parameter '=' Value |
Parameter '+=' Value |
Parameter '-=' Value |
'!'* Parameter
Parameters may be flags, integer values, strings, or lists. Flags are
implicitly boolean and can be turned off via the `!' operator. Some
integer, string and list parameters may also be used in a boolean context
to disable them. Values may be enclosed in double quotes ("") when they
contain multiple words. Special characters may be escaped with a backslash
(`\').
To include a literal backslash character in a command line argument you
must escape the backslash twice. For example, to match `\n' as part of a
command line argument, you must use `\\\\n' in the sudoers file. This is
due to there being two levels of escaping, one in the sudoers parser itself
and another when command line arguments are matched by the fnmatch(3) or
regexec(3) function.
Lists have two additional assignment operators, `+=' and `-='. These
operators are used to add to and delete from a list respectively. It is
not an error to use the `-=' operator to remove an element that does not
exist in a list.
Defaults entries are parsed in the following order: global, host, user, and
runas Defaults first, then command defaults. If there are multiple
Defaults settings of the same type, the last matching setting is used. The
following Defaults settings are parsed before all others since they may
affect subsequent entries: fqdn, group_plugin, runas_default,
sudoers_locale.
See SUDOERS OPTIONS for a list of supported Defaults parameters.
User specification
User_Spec ::= User_List Host_List '=' Cmnd_Spec_List \
(':' Host_List '=' Cmnd_Spec_List)*
Cmnd_Spec_List ::= Cmnd_Spec |
Cmnd_Spec ',' Cmnd_Spec_List
Cmnd_Spec ::= Runas_Spec? Option_Spec* (Tag_Spec ':')* Cmnd
Runas_Spec ::= '(' Runas_List? (':' Runas_List)? ')'
Option_Spec ::= (Date_Spec | Timeout_Spec | Chdir_Spec | Chroot_Spec)
Date_Spec ::= ('NOTBEFORE=timestamp' | 'NOTAFTER=timestamp')
Timeout_Spec ::= 'TIMEOUT=timeout'
Chdir_Spec ::= 'CWD=directory'
Chroot_Spec ::= 'CHROOT=directory'
Tag_Spec ::= ('EXEC' | 'NOEXEC' | 'FOLLOW' | 'NOFOLLOW' |
'LOG_INPUT' | 'NOLOG_INPUT' | 'LOG_OUTPUT' |
'NOLOG_OUTPUT' | 'MAIL' | 'NOMAIL' | 'INTERCEPT' |
'NOINTERCEPT' | 'PASSWD' | 'NOPASSWD' | 'SETENV' |
'NOSETENV')
A user specification determines which commands a user may run (and as what
user) on specified hosts. By default, commands are run as root (unless
runas_default has been set to a different value) but this can also be
changed on a per-command basis.
The basic structure of a user specification is "who where = (as_whom)
what". Let's break that down into its constituent parts:
Runas_Spec
A Runas_Spec determines the user and/or the group that a command may be run
as. A fully-specified Runas_Spec consists of two Runas_Lists (as defined
above) separated by a colon (`:') and enclosed in a set of parentheses.
The first Runas_List indicates which users the command may be run as via
the -u option. The second defines a list of groups that may be specified
via the -g option (in addition to any of the target user's groups). If
both Runas_Lists are specified, the command may be run with any combination
of users and groups listed in their respective Runas_Lists. If only the
first is specified, the command may be run as any user in the list and,
optionally, with any group the target user belongs to. If the first
Runas_List is empty but the second is specified, the command may be run as
the invoking user with the group set to any listed in the Runas_List. If
both Runas_Lists are empty, the command may only be run as the invoking
user and the group, if specified, must be one that the invoking user is a
member of. If no Runas_Spec is specified, the command may only be run as
the runas_default user (root by default) and the group, if specified, must
be one that the runas_default user is a member of.
A Runas_Spec sets the default for the commands that follow it. What this
means is that for the entry:
dgb boulder = (operator) /bin/ls, /bin/kill, /usr/bin/lprm
The user dgb may run /bin/ls, /bin/kill, and /usr/bin/lprm on the host
boulder--but only as operator. For example:
$ sudo -u operator /bin/ls
It is also possible to override a Runas_Spec later on in an entry. If we
modify the entry like so:
dgb boulder = (operator) /bin/ls, (root) /bin/kill, /usr/bin/lprm
Then user dgb is now allowed to run /bin/ls as operator, but /bin/kill and
/usr/bin/lprm as root.
We can extend this to allow dgb to run /bin/ls with either the user or
group set to operator:
dgb boulder = (operator : operator) /bin/ls, (root) /bin/kill,\
/usr/bin/lprm
While the group portion of the Runas_Spec permits the user to run as
command with that group, it does not force the user to do so. If no group
is specified on the command line, the command will run with the group
listed in the target user's password database entry. The following would
all be permitted by the sudoers entry above:
$ sudo -u operator /bin/ls
$ sudo -u operator -g operator /bin/ls
$ sudo -g operator /bin/ls
In the following example, user tcm may run commands that access a modem
device file with the dialer group.
tcm boulder = (:dialer) /usr/bin/tip, /usr/bin/cu,\
/usr/local/bin/minicom
In this example only the group will be set, the command still runs as user
tcm. For example:
$ sudo -g dialer /usr/bin/cu
Multiple users and groups may be present in a Runas_Spec, in which case the
user may select any combination of users and groups via the -u and -g
options. In this example:
alan ALL = (root, bin : operator, system) ALL
user alan may run any command as either user root or bin, optionally
setting the group to operator or system.
Option_Spec
A Cmnd may have zero or more options associated with it. Options may
consist of start and/or end dates and command timeouts. Once an option is
set for a Cmnd, subsequent Cmnds in the Cmnd_Spec_List, inherit that option
unless it is overridden by another option. Option names are reserved words
in sudoers. This means that none of the valid option names (see below) can
be used when declaring an alias.
Date_Spec
sudoers rules can be specified with a start and end date via the NOTBEFORE
and NOTAFTER settings. The time stamp must be specified in "Generalized
Time" as defined by RFC 4517. The format is effectively `yyyymmddHHMMSSZ'
where the minutes and seconds are optional. The `Z' suffix indicates that
the time stamp is in Coordinated Universal Time (UTC). It is also possible
to specify a timezone offset from UTC in hours and minutes instead of a
`Z'. For example, `-0500' would correspond to Eastern Standard time in the
US. As an extension, if no `Z' or timezone offset is specified, local time
will be used.
The following are all valid time stamps:
20170214083000Z
2017021408Z
20160315220000-0500
20151201235900
Timeout_Spec
A command may have a timeout associated with it. If the timeout expires
before the command has exited, the command will be terminated. The timeout
may be specified in combinations of days, hours, minutes, and seconds with
a single-letter case-insensitive suffix that indicates the unit of time.
For example, a timeout of 7 days, 8 hours, 30 minutes, and 10 seconds would
be written as `7d8h30m10s'. If a number is specified without a unit,
seconds are assumed. Any of the days, minutes, hours, or seconds may be
omitted. The order must be from largest to smallest unit and a unit may
not be specified more than once.
The following are all valid timeout values: `7d8h30m10s', `14d', `8h30m',
`600s', `3600'. The following are invalid timeout values: `12m2w1d',
`30s10m4h', `1d2d3h'.
This setting is only supported by version 1.8.20 or higher.
Chdir_Spec
The working directory that the command will be run in can be specified
using the CWD setting. The directory must be a fully-qualified path name
beginning with a `/' or `~' character, or the special value "*". A value
of "*" indicates that the user may specify the working directory by running
sudo with the -D option. By default, commands are run from the invoking
user's current working directory, unless the -i option is given. Path
names of the form ~user/path/name are interpreted as being relative to the
named user's home directory. If the user name is omitted, the path will be
relative to the runas user's home directory.
This setting is only supported by version 1.9.3 or higher.
Chroot_Spec
The root directory that the command will be run in can be specified using
the CHROOT setting. The directory must be a fully-qualified path name
beginning with a `/' or `~' character, or the special value "*". A value
of "*" indicates that the user may specify the root directory by running
sudo with the -R option. This setting can be used to run the command in a
chroot(2) "sandbox" similar to the chroot(8) utility. Path names of the
form ~user/path/name are interpreted as being relative to the named user's
home directory. If the user name is omitted, the path will be relative to
the runas user's home directory.
This setting is only supported by version 1.9.3 or higher.
Tag_Spec
A command may have zero or more tags associated with it. The following tag
values are supported: EXEC, NOEXEC, FOLLOW, NOFOLLOW, LOG_INPUT,
NOLOG_INPUT, LOG_OUTPUT, NOLOG_OUTPUT, MAIL, NOMAIL, INTERCEPT,
NOINTERCEPT, PASSWD, NOPASSWD, SETENV, and NOSETENV. Once a tag is set on
a Cmnd, subsequent Cmnds in the Cmnd_Spec_List, inherit the tag unless it
is overridden by the opposite tag (in other words, PASSWD overrides
NOPASSWD and NOEXEC overrides EXEC).
EXEC and NOEXEC
If sudo has been compiled with noexec support and the underlying
operating system supports it, the NOEXEC tag can be used to prevent a
dynamically-linked executable from running further commands itself.
In the following example, user aaron may run /usr/bin/more and
/usr/bin/vi but shell escapes will be disabled.
aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi
See the Preventing shell escapes section below for more details on how
NOEXEC works and whether or not it will work on your system.
FOLLOW and NOFOLLOW
Starting with version 1.8.15, sudoedit will not open a file that is a
symbolic link unless the sudoedit_follow flag is enabled. The FOLLOW and
NOFOLLOW tags override the value of sudoedit_follow and can be used to
permit (or deny) the editing of symbolic links on a per-command basis.
These tags are only effective for the sudoedit command and are ignored
for all other commands.
LOG_INPUT and NOLOG_INPUT
These tags override the value of the log_input flag on a per-command
basis. For more information, see I/O LOGGING.
LOG_OUTPUT and NOLOG_OUTPUT
These tags override the value of the log_output flag on a per-command
basis. For more information, see I/O LOGGING.
MAIL and NOMAIL
These tags provide fine-grained control over whether mail will be sent
when a user runs a command by overriding the value of the mail_all_cmnds
flag on a per-command basis. They have no effect when sudo is run with
the -l or -v options. A NOMAIL tag will also override the mail_always
and mail_no_perms options. For more information, see the descriptions of
mail_all_cmnds, mail_always, and mail_no_perms in the SUDOERS OPTIONS
section below.
PASSWD and NOPASSWD
By default, sudo requires that a user authenticate before running a
command. This behavior can be modified via the NOPASSWD tag. Like a
Runas_Spec, the NOPASSWD tag sets a default for the commands that follow
it in the Cmnd_Spec_List. Conversely, the PASSWD tag can be used to
reverse things. For example:
ray rushmore = NOPASSWD: /bin/kill, /bin/ls, /usr/bin/lprm
would allow the user ray to run /bin/kill, /bin/ls, and /usr/bin/lprm as
root on the machine "rushmore" without authenticating himself. If we
only want ray to be able to run /bin/kill without a password the entry
would be:
ray rushmore = NOPASSWD: /bin/kill, PASSWD: /bin/ls, /usr/bin/lprm
Note, however, that the PASSWD tag has no effect on users who are in the
group specified by the exempt_group setting.
By default, if the NOPASSWD tag is applied to any of a user's entries for
the current host, the user will be able to run `sudo -l' without a
password. Additionally, a user may only run `sudo -v' without a password
if all of the user's entries for the current host have the NOPASSWD tag.
This behavior may be overridden via the verifypw and listpw options.
SETENV and NOSETENV
These tags override the value of the setenv flag on a per-command basis.
If SETENV has been set for a command, the user may disable the env_reset
flag from the command line via the -E option. Additionally, environment
variables set on the command line are not subject to the restrictions
imposed by env_check, env_delete, or env_keep. As such, only trusted
users should be allowed to set variables in this manner. If the command
matched is ALL, the SETENV tag is implied for that command; this default
may be overridden by use of the NOSETENV tag.
INTERCEPT and NOINTERCEPT
If sudo has been compiled with intercept support and the underlying
operating system supports it, the INTERCEPT tag can be used to cause
programs spawned by a command to be validated against sudoers and logged
just like they would be if run through sudo directly. This is useful in
conjunction with commands that allow shell escapes such as editors,
shells, and paginators. There is additional overhead due to the policy
check that may add latency when running commands such as shell scripts
that execute a large number of sub-commands. For interactive commands,
such as a shell or editor, the overhead is not usually noticeable.
In the following example, user chuck may run any command on the machine
"research" in intercept mode.
chuck research = INTERCEPT: ALL
See the Preventing shell escapes section below for more details on how
INTERCEPT works and whether or not it will work on your system.
Wildcards
sudo allows shell-style wildcards (aka meta or glob characters) to be used
in host names, path names, and command line arguments in the sudoers file.
Wildcard matching is done via the glob(3) and fnmatch(3) functions as
specified by IEEE Std 1003.1 ("POSIX.1").
* Matches any set of zero or more characters (including white space).
? Matches any single character (including white space).
[...] Matches any character in the specified range.
[!...] Matches any character not in the specified range.
\x For any character `x', evaluates to `x'. This is used to escape
special characters such as: `*', `?', `[', and `]'.
These are not regular expressions. Unlike a regular expression there is no
way to match one or more characters within a range.
Character classes may be used if your system's glob(3) and fnmatch(3)
functions support them. However, because the `:' character has special
meaning in sudoers, it must be escaped. For example:
/bin/ls [[\:alpha\:]]*
Would match any file name beginning with a letter.
A forward slash (`/') will not be matched by wildcards used in the file
name portion of the command. This is to make a path like:
/usr/bin/*
match /usr/bin/who but not /usr/bin/X11/xterm.
When matching the command line arguments, however, a slash does get matched
by wildcards since command line arguments may contain arbitrary strings and
not just path names.
Wildcards in command line arguments should be used with care.
Wildcards can match any character, including white space. In most cases,
it is safer to use a regular expression to match command line arguments.
For more information, see Wildcards in command arguments below.
Exceptions to wildcard rules
The following exceptions apply to the above rules:
"" If the empty string `""' is the only command line argument in the
sudoers file entry it means that command is not allowed to be run
with any arguments.
sudoedit Command line arguments to the sudoedit built-in command should
always be path names, so a forward slash (`/') will not be
matched by a wildcard.
Regular expressions
Starting with version 1.9.10, it is possible to use regular expressions for
path names and command line arguments. Regular expressions are more
expressive than shell-style wildcards and are usually safer because they
provide a greater degree of control when matching. The type of regular
expressions supported by sudoers are POSIX extended regular expressions,
similar to those used by the egrep(1) utility. They are usually documented
in the regex(7) or re_format(7) manual, depending on the system. As an
extension, if the regular expression begins with "(?i)", it will be matched
in a case-insensitive manner.
In sudoers, regular expressions must start with a `^' character and end
with a `$'. This makes it explicit what is, or is not, a regular
expression. Either the path name, the command line arguments or both may
be regular expressions. Because the path name and arguments are matched
separately, it is even possible to use wildcards for the path name and
regular expressions for the arguments. It is not possible to use a single
regular expression to match both the command and its arguments. Regular
expressions in sudoers are limited to 1024 characters.
There is no need to escape sudoers special characters in a regular
expression other than the pound sign (`#').
In the following example, user john can run the passwd(1) command as root
on any host but is not allowed to change root's password. This kind of
rule is impossible to express safely using wildcards.
john ALL = /usr/bin/passwd ^[a-zA-Z0-9_]+$,\
!/usr/bin/passwd root
It is also possible to use a regular expression in conjunction with
sudoedit rules. The following rule would give user bob the ability to edit
the /etc/motd, /etc/issue, and /etc/hosts files only.
bob ALL = sudoedit ^/etc/(motd|issue|hosts)$
Regular expressions may also be used to match the command itself. In this
example, a regular expression is used to allow user sid to run the
/usr/sbin/groupadd, /usr/sbin/groupmod, /usr/sbin/groupdel,
/usr/sbin/useradd, /usr/sbin/usermod, and /usr/sbin/userdel commands as
root.
sid ALL = ^/usr/sbin/(group|user)(add|mod|del)$
One disadvantage of using a regular expression to match the command name is
that it is not possible to match relative paths such as ./useradd or
../sbin/useradd. This has security implications when a regular expression
is used for the command name in conjunction with the negation operator,
`!', as such rules can be trivially bypassed. Because of this, using a
negated regular expression for the command name is strongly discouraged.
This does not apply to negated commands that only use a regular expression
to match the command arguments. See Regular expressions in command names
below for more information.
Including other files from within sudoers
It is possible to include other sudoers files from within the sudoers file
currently being parsed using the @include and @includedir directives. For
compatibility with sudo versions prior to 1.9.1, #include and #includedir
are also accepted.
An include file can be used, for example, to keep a site-wide sudoers file
in addition to a local, per-machine file. For the sake of this example the
site-wide sudoers file will be /etc/sudoers and the per-machine one will be
/etc/sudoers.local. To include /etc/sudoers.local from within /etc/sudoers
one would use the following line in /etc/sudoers:
@include /etc/sudoers.local
When sudo reaches this line it will suspend processing of the current file
(/etc/sudoers) and switch to /etc/sudoers.local. Upon reaching the end of
/etc/sudoers.local, the rest of /etc/sudoers will be processed. Files that
are included may themselves include other files. A hard limit of 128
nested include files is enforced to prevent include file loops.
Starting with version 1.9.1, the path to the include file may contain white
space if it is escaped with a backslash (`\'). Alternately, the entire
path may be enclosed in double quotes (""), in which case no escaping is
necessary. To include a literal backslash in the path, `\\' should be
used.
If the path to the include file is not fully-qualified (does not begin with
a `/'), it must be located in the same directory as the sudoers file it was
included from. For example, if /etc/sudoers contains the line:
@include sudoers.local
the file that will be included is /etc/sudoers.local.
The file name may also include the `%h' escape, signifying the short form
of the host name. In other words, if the machine's host name is "xerxes",
then
@include /etc/sudoers.%h
will cause sudo to include the file /etc/sudoers.xerxes.
The @includedir directive can be used to create a sudoers.d directory that
the system package manager can drop sudoers file rules into as part of
package installation. For example, given:
@includedir /etc/sudoers.d
sudo will suspend processing of the current file and read each file in
/etc/sudoers.d, skipping file names that end in `~' or contain a `.'
character to avoid causing problems with package manager or editor
temporary/backup files.
Files are parsed in sorted lexical order. That is, /etc/sudoers.d/01_first
will be parsed before /etc/sudoers.d/10_second. Be aware that because the
sorting is lexical, not numeric, /etc/sudoers.d/1_whoops would be loaded
after /etc/sudoers.d/10_second. Using a consistent number of leading
zeroes in the file names can be used to avoid such problems. After parsing
the files in the directory, control returns to the file that contained the
@includedir directive.
Unlike files included via @include, visudo will not edit the files in a
@includedir directory unless one of them contains a syntax error. It is
still possible to run visudo with the -f flag to edit the files directly,
but this will not catch the redefinition of an alias that is also present
in a different file.
Other special characters and reserved words
The pound sign (`#') is used to indicate a comment (unless it is part of a
#include directive or unless it occurs in the context of a user name and is
followed by one or more digits, in which case it is treated as a user-ID).
Both the comment character and any text after it, up to the end of the
line, are ignored.
The reserved word ALL is a built-in alias that always causes a match to
succeed. It can be used wherever one might otherwise use a Cmnd_Alias,
User_Alias, Runas_Alias, or Host_Alias. Attempting to define an alias
named ALL will result in a syntax error. Using ALL can be dangerous since
in a command context, it allows the user to run any command on the system.
The following option names permitted in an Option_Spec are also considered
reserved words: CHROOT, TIMEOUT, CWD, NOTBEFORE and NOTAFTER. Attempting
to define an alias with the same name as one of the options will result in
a syntax error.
An exclamation point (`!') can be used as a logical not operator in a list
or alias as well as in front of a Cmnd. This allows one to exclude certain
values. For the `!' operator to be effective, there must be something for
it to exclude. For example, to match all users except for root one would
use:
ALL, !root
If the ALL, is omitted, as in:
!root
it would explicitly deny root but not match any other users. This is
different from a true "negation" operator.
Note, however, that using a `!' in conjunction with the built-in ALL alias
to allow a user to run "all but a few" commands rarely works as intended
(see SECURITY NOTES below).
Long lines can be continued with a backslash (`\') as the last character on
the line.
White space between elements in a list as well as special syntactic
characters in a User Specification (`=', `:', `(', `)') is optional.
The following characters must be escaped with a backslash (`\') when used
as part of a word (e.g., a user name or host name): `!', `=', `:', `,',
`(', `)', `\'.
SUDOERS OPTIONS
sudo's behavior can be modified by Default_Entry lines, as explained
earlier. A list of all supported Defaults parameters, grouped by type, are
listed below.
Boolean Flags:
always_query_group_plugin
If a group_plugin is configured, use it to resolve groups
of the form `%group' as long as there is not also a
system group of the same name. Normally, only groups of
the form `%:group' are passed to the group_plugin. This
flag is off by default.
always_set_home If enabled, sudo will set the HOME environment variable
to the home directory of the target user (which is the
runas_default user unless the -u option is used). This
flag is largely obsolete and has no effect unless the
env_reset flag has been disabled or HOME is present in
the env_keep list, both of which are strongly
discouraged. This flag is off by default.
authenticate If set, users must authenticate themselves via a password
(or other means of authentication) before they may run
commands. This default may be overridden via the PASSWD
and NOPASSWD tags. This flag is on by default.
case_insensitive_group
If enabled, group names in sudoers will be matched in a
case insensitive manner. This may be necessary when
users are stored in LDAP or AD. This flag is on by
default.
case_insensitive_user
If enabled, user names in sudoers will be matched in a
case insensitive manner. This may be necessary when
groups are stored in LDAP or AD. This flag is on by
default.
closefrom_override
If set, the user may use the -C option which overrides
the default starting point at which sudo begins closing
open file descriptors. This flag is off by default.
compress_io If set, and sudo is configured to log a command's input
or output, the I/O logs will be compressed using zlib.
This flag is on by default when sudo is compiled with
zlib support.
exec_background By default, sudo runs a command as the foreground process
as long as sudo itself is running in the foreground.
When the exec_background flag is enabled and the command
is being run in a pseudo-terminal (due to I/O logging or
the use_pty flag), the command will be run as a
background process. Attempts to read from the
controlling terminal (or to change terminal settings)
will result in the command being suspended with the
SIGTTIN signal (or SIGTTOU in the case of terminal
settings). If this happens when sudo is a foreground
process, the command will be granted the controlling
terminal and resumed in the foreground with no user
intervention required. The advantage of initially
running the command in the background is that sudo need
not read from the terminal unless the command explicitly
requests it. Otherwise, any terminal input must be
passed to the command, whether it has required it or not
(the kernel buffers terminals so it is not possible to
tell whether the command really wants the input). This
is different from historic sudo behavior or when the
command is not being run in a pseudo-terminal.
For this to work seamlessly, the operating system must
support the automatic restarting of system calls.
Unfortunately, not all operating systems do this by
default, and even those that do may have bugs. For
example, macOS fails to restart the tcgetattr(3) and
tcsetattr(3) functions (this is a bug in macOS).
Furthermore, because this behavior depends on the command
stopping with the SIGTTIN or SIGTTOU signals, programs
that catch these signals and suspend themselves with a
different signal (usually SIGTOP) will not be
automatically foregrounded. Some versions of the linux
su(1) command behave this way. This flag is off by
default.
This setting is only supported by version 1.8.7 or
higher. It has no effect unless I/O logging is enabled
or the use_pty flag is enabled.
env_editor If set, visudo will use the value of the SUDO_EDITOR,
VISUAL or EDITOR environment variables before falling
back on the default editor list. visudo is typically run
as root so this flag may allow a user with visudo
privileges to run arbitrary commands as root without
logging. An alternative is to place a colon-separated
list of "safe" editors int the editor setting. visudo
will then only use SUDO_EDITOR, VISUAL or EDITOR if they
match a value specified in editor. If the env_reset flag
is enabled, the SUDO_EDITOR, VISUAL and/or EDITOR
environment variables must be present in the env_keep
list for the env_editor flag to function when visudo is
invoked via sudo. This flag is on by default.
env_reset If set, sudo will run the command in a minimal
environment containing the TERM, PATH, HOME, MAIL, SHELL,
LOGNAME, USER and SUDO_* variables. Any variables in the
caller's environment or in the file specified by the
restricted_env_file setting that match the env_keep and
env_check lists are then added, followed by any variables
present in the file specified by the env_file setting (if
any). The contents of the env_keep and env_check lists,
as modified by global Defaults parameters in sudoers, are
displayed when sudo is run by root with the -V option.
If the secure_path setting is enabled, its value will be
used for the PATH environment variable. This flag is on
by default.
fast_glob Normally, sudo uses the glob(3) function to do shell-
style globbing when matching path names. However, since
it accesses the file system, glob(3) can take a long time
to complete for some patterns, especially when the
pattern references a network file system that is mounted
on demand (auto mounted). The fast_glob flag causes sudo
to use the fnmatch(3) function, which does not access the
file system to do its matching. The disadvantage of
fast_glob is that it is unable to match relative paths
such as ./ls or ../bin/ls. This has security
implications when path names that include globbing
characters are used with the negation operator, `!', as
such rules can be trivially bypassed. As such, this flag
should not be used when the sudoers file contains rules
that contain negated path names which include globbing
characters. This flag is off by default.
log_passwords Most programs that require a user's password will disable
echo before reading the password to avoid displaying the
plaintext password on the screen. However, if terminal
input is being logged (see I/O LOGGING), the password
will still be present in the I/O log. If the
log_passwords option is disabled, sudoers will attempt to
prevent passwords from being logged. It does this by
using the regular expressions in passprompt_regex to
match a password prompt in the terminal output buffer.
When a match is found, input characters in the I/O log
will be replaced with `*' until either a line feed or
carriage return is found in the terminal input or a new
terminal output buffer is received. If, however, a
program displays characters as the user types (such as
sudo when pwfeedback is set), only the first character of
the password will be replaced in the I/O log. This
option has no effect unless log_input or log_ttyin are
also set. This flag is on by default.
This setting is only supported by version 1.9.10 or
higher.
fqdn Set this flag if you want to put fully qualified host
names in the sudoers file when the local host name (as
returned by the `hostname' command) does not contain the
domain name. In other words, instead of myhost you would
use myhost.mydomain.edu. You may still use the short
form if you wish (and even mix the two). This flag is
only effective when the "canonical" host name, as
returned by the getaddrinfo(3) or gethostbyname(3)
function, is a fully-qualified domain name. This is
usually the case when the system is configured to use DNS
for host name resolution.
If the system is configured to use the /etc/hosts file in
preference to DNS, the "canonical" host name may not be
fully-qualified. The order that sources are queried for
host name resolution is usually specified in the
/etc/nsswitch.conf, /etc/netsvc.conf, /etc/host.conf, or,
in some cases, /etc/resolv.conf file. In the /etc/hosts
file, the first host name of the entry is considered to
be the "canonical" name; subsequent names are aliases
that are not used by sudoers. For example, the following
hosts file line for the machine "xyzzy" has the fully-
qualified domain name as the "canonical" host name, and
the short version as an alias.
192.168.1.1 xyzzy.sudo.ws xyzzy
If the machine's hosts file entry is not formatted
properly, the fqdn flag will not be effective if it is
queried before DNS.
Beware that when using DNS for host name resolution,
turning on fqdn requires sudoers to make DNS lookups
which renders sudo unusable if DNS stops working (for
example if the machine is disconnected from the network).
Just like with the hosts file, you must use the
"canonical" name as DNS knows it. That is, you may not
use a host alias (CNAME entry) due to performance issues
and the fact that there is no way to get all aliases from
DNS.
This flag is off by default.
ignore_audit_errors
Allow commands to be run even if sudoers cannot write to
the audit log. If enabled, an audit log write failure is
not treated as a fatal error. If disabled, a command may
only be run after the audit event is successfully
written. This flag is only effective on systems for
which sudoers supports audit logging, including FreeBSD,
Linux, macOS, and Solaris. This flag is on by default.
ignore_dot If set, sudo will ignore "." or "" (both denoting the
current directory) in the PATH environment variable; the
PATH itself is not modified. This flag is on by default.
ignore_iolog_errors
Allow commands to be run even if sudoers cannot write to
the I/O log (local or remote). If enabled, an I/O log
write failure is not treated as a fatal error. If
disabled, the command will be terminated if the I/O log
cannot be written to. This flag is off by default.
ignore_logfile_errors
Allow commands to be run even if sudoers cannot write to
the log file. If enabled, a log file write failure is
not treated as a fatal error. If disabled, a command may
only be run after the log file entry is successfully
written. This flag only has an effect when sudoers is
configured to use file-based logging via the logfile
setting. This flag is on by default.
ignore_local_sudoers
If set via LDAP, parsing of /opt/local/etc/sudoers will
be skipped. This is intended for sites that wish to
prevent the usage of local sudoers files so that only
LDAP is used. This thwarts the efforts of rogue
operators who would attempt to add roles to
/opt/local/etc/sudoers. When this flag is enabled,
/opt/local/etc/sudoers does not even need to exist.
Since this flag tells sudo how to behave when no specific
LDAP entries have been matched, this sudoOption is only
meaningful for the `cn=defaults' section. This flag is
off by default.
ignore_unknown_defaults
If set, sudo will not produce a warning if it encounters
an unknown Defaults entry in the sudoers file or an
unknown sudoOption in LDAP. This flag is off by default.
insults If set, sudo will insult users when they enter an
incorrect password. This flag is off by default.
log_allowed If set, sudoers will log commands allowed by the policy
to the system audit log (where supported) as well as to
syslog and/or a log file. This flag is on by default.
This setting is only supported by version 1.8.29 or
higher.
log_denied If set, sudoers will log commands denied by the policy to
the system audit log (where supported) as well as to
syslog and/or a log file. This flag is on by default.
This setting is only supported by version 1.8.29 or
higher.
log_exit_status If set, sudoers will log the exit value of commands that
are run to syslog and/or a log file. If a command was
terminated by a signal, the signal name is logged as
well. This flag is off by default.
This setting is only supported by version 1.9.8 or
higher.
log_host If set, the host name will be included in log entries
written to the file configured by the logfile setting.
This flag is off by default.
log_input If set, sudo will run the command in a pseudo-terminal
(if sudo was run from a terminal) and log all user input.
If the standard input is not connected to the user's
terminal, due to I/O redirection or because the command
is part of a pipeline, that input is also logged. For
more information about I/O logging, see the I/O LOGGING
section. This flag is off by default.
log_output If set, sudo will run the command in a pseudo-terminal
(if sudo was run from a terminal) and log all output that
is sent to the user's terminal, the standard output or
the standard error. If the standard output or standard
error is not connected to the user's terminal, due to I/O
redirection or because the command is part of a pipeline,
that output is also logged. For more information about
I/O logging, see the I/O LOGGING section. This flag is
off by default.
log_server_keepalive
If set, sudo will enable the TCP keepalive socket option
on the connection to the log server. This enables the
periodic transmission of keepalive messages to the
server. If the server does not respond to a message, the
connection will be closed and the running command will be
terminated unless the ignore_iolog_errors flag (I/O
logging enabled) or the ignore_log_errors flag (I/O
logging disabled) is set. This flag is on by default.
This setting is only supported by version 1.9.0 or
higher.
log_server_verify
If set, the server certificate received during the TLS
handshake must be valid and it must contain either the
server name (from log_servers) or its IP address. If
either of these conditions is not met, the TLS handshake
will fail. This flag is on by default.
This setting is only supported by version 1.9.0 or
higher.
log_stderr If set, sudo will log the standard error if it is not
connected to the user's terminal. This can be used to
log output to a pipe or redirected to a file. This flag
is off by default but is enabled when either the
log_output flag or the LOG_OUTPUT command tag is set.
log_stdin If set, sudo will log the standard input if it is not
connected to the user's terminal. This can be used to
log input from a pipe or redirected from a file. This
flag is off by default but is enabled when either the
log_input flag or the LOG_INPUT command tag is set.
log_stdout If set, sudo will log the standard output if it is not
connected to the user's terminal. This can be used to
log output to a pipe or redirected to a file. This flag
is off by default but is enabled when either the
log_output flag or the LOG_OUTPUT command tag is set.
log_subcmds If set, sudoers will log when a command spawns a child
process and executes a program using the execve(2),
execl(3), execle(3), execlp(3), execv(3), execvp(3),
execvpe(3), or system(3) library functions. For example,
if a shell is run by sudo, the individual commands run
via the shell will be logged. This flag is off by
default.
The log_subcmds flag uses the same underlying mechanism
as the intercept setting. See Preventing shell escapes
for more information on what systems support this option
and its limitations. This setting is only supported by
version 1.9.8 or higher and is incompatible with SELinux
RBAC support unless the system supports seccomp(2) filter
mode.
log_ttyin If set, sudo will run the command in a pseudo-terminal
and log user keystrokes sent to the user's terminal, if
one is present. This flag is off by default but is
enabled when either the log_input flag or the LOG_INPUT
command tag is set. If no terminal is present, for
example when running a remote command using ssh(1), this
flag will have no effect.
log_ttyout If set, sudo will run the command in a pseudo-terminal
and log all output displayed on the user's terminal, if
one is present. This flag is off by default but is
enabled when either the log_output flag or the LOG_OUTPUT
command tag is set. If no terminal is present, for
example when running a remote command using ssh(1), this
flag will have no effect.
log_year If set, the four-digit year will be logged in the (non-
syslog) sudo log file. This flag is off by default.
long_otp_prompt When validating with a One Time Password (OTP) scheme
such as S/Key or OPIE, a two-line prompt is used to make
it easier to cut and paste the challenge to a local
window. It's not as pretty as the default but some
people find it more convenient. This flag is off by
default.
mail_all_cmnds Send mail to the mailto user every time a user attempts
to run a command via sudo (this includes sudoedit). No
mail will be sent if the user runs sudo with the -l or -v
option unless there is an authentication error and the
mail_badpass flag is also set. This flag is off by
default.
mail_always Send mail to the mailto user every time a user runs sudo.
This flag is off by default.
mail_badpass Send mail to the mailto user if the user running sudo
does not enter the correct password. If the command the
user is attempting to run is not permitted by sudoers and
one of the mail_all_cmnds, mail_always, mail_no_host,
mail_no_perms or mail_no_user flags are set, this flag
will have no effect. This flag is off by default.
mail_no_host If set, mail will be sent to the mailto user if the
invoking user exists in the sudoers file, but is not
allowed to run commands on the current host. This flag
is off by default.
mail_no_perms If set, mail will be sent to the mailto user if the
invoking user is allowed to use sudo but the command they
are trying is not listed in their sudoers file entry or
is explicitly denied. This flag is off by default.
mail_no_user If set, mail will be sent to the mailto user if the
invoking user is not in the sudoers file. This flag is
on by default.
match_group_by_gid
By default, sudoers will look up each group the user is a
member of by group-ID to determine the group name (this
is only done once). The resulting list of the user's
group names is used when matching groups listed in the
sudoers file. This works well on systems where the
number of groups listed in the sudoers file is larger
than the number of groups a typical user belongs to. On
systems where group lookups are slow, where users may
belong to a large number of groups, or where the number
of groups listed in the sudoers file is relatively small,
it may be prohibitively expensive and running commands
via sudo may take longer than normal. On such systems it
may be faster to use the match_group_by_gid flag to avoid
resolving the user's group-IDs to group names. In this
case, sudoers must look up any group name listed in the
sudoers file and use the group-ID instead of the group
name when determining whether the user is a member of the
group.
If match_group_by_gid is enabled, group database lookups
performed by sudoers will be keyed by group name as
opposed to group-ID. On systems where there are multiple
sources for the group database, it is possible to have
conflicting group names or group-IDs in the local
/etc/group file and the remote group database. On such
systems, enabling or disabling match_group_by_gid can be
used to choose whether group database queries are
performed by name (enabled) or ID (disabled), which may
aid in working around group entry conflicts.
The match_group_by_gid flag has no effect when sudoers
data is stored in LDAP. This flag is off by default.
This setting is only supported by version 1.8.18 or
higher.
intercept If set, all commands run via sudo will behave as if the
INTERCEPT tag has been set, unless overridden by an
NOINTERCEPT tag. See the description of INTERCEPT and
NOINTERCEPT above as well as the Preventing shell escapes
section at the end of this manual. This flag is off by
default.
This setting is only supported by version 1.9.8 or higher
and is incompatible with SELinux RBAC support unless the
system supports seccomp(2) filter mode.
intercept_allow_setid
On most systems, the dynamic loader will ignore
LD_PRELOAD (or the equivalent) when running set-user-ID
and set-group-ID programs, effectively disabling
intercept mode. To prevent this from happening, sudoers
will not permit a set-user-ID or set-group-ID program to
be run in intercept mode unless intercept_allow_setid is
enable. This flag has no effect unless the intercept
flag is enabled or the INTERCEPT tag has been set for the
command. This flag is on by default when the
intercept_type option is set to trace, otherwise it
default to off.
This setting is only supported by version 1.9.8 or
higher.
intercept_authenticate
If set, commands run by an intercepted process must be
authenticated when the user's time stamp is not current.
For example, if a shell is run with intercept enabled, as
soon as the invoking user's time stamp is out of date,
subsequent commands will need to be authenticated. This
flag has no effect unless the intercept flag is enabled
or the INTERCEPT tag has been set for the command. This
flag is off by default.
This setting is only supported by version 1.9.8 or
higher.
intercept_verify If set, sudo will attempt to verify that a command run in
intercept mode has the expected path name, command line
arguments and environment.
The process will be stopped after execve(2) has completed
but before the new command has had a chance to run. To
verify the command, sudo will read the command's path
from /proc/PID/exe, the command line arguments and
environment from the process's memory, and compare them
against the arguments that were passed to execve(2). In
the event of a mismatch, the command will be sent a
SIGKILL signal and terminated.
This can help prevent a time of check versus time of use
issue with intercept mode where the execve(2) arguments
could be altered after the sudoers policy check. The
checks can only be performed if the proc(5) file system
is available. This flag has no effect unless the
intercept flag is enabled or the INTERCEPT tag has been
set for the command and the intercept_type option is set
to trace. This flag is on by default.
This setting is only supported by version 1.9.12 or
higher.
netgroup_tuple If set, netgroup lookups will be performed using the full
netgroup tuple: host name, user name, and domain (if one
is set). Historically, sudo only matched the user name
and domain for netgroups used in a User_List and only
matched the host name and domain for netgroups used in a
Host_List. This flag is off by default.
noexec If set, all commands run via sudo will behave as if the
NOEXEC tag has been set, unless overridden by an EXEC
tag. See the description of EXEC and NOEXEC above as
well as the Preventing shell escapes section at the end
of this manual. This flag is off by default.
noninteractive_auth
If set, authentication will be attempted even in non-
interactive mode (when sudo's -n option is specified).
This allows authentication methods that don't require
user interaction to succeed. Authentication methods that
require input from the user's terminal will still fail.
If disabled, authentication will not be attempted in non-
interactive mode. This flag is off by default.
This setting is only supported by version 1.9.10 or
higher.
pam_acct_mgmt On systems that use PAM for authentication, sudo will
perform PAM account validation for the invoking user by
default. The actual checks performed depend on which PAM
modules are configured. If enabled, account validation
will be performed regardless of whether or not a password
is required. This flag is on by default.
This setting is only supported by version 1.8.28 or
higher.
pam_rhost On systems that use PAM for authentication, sudo will set
the PAM remote host value to the name of the local host
when the pam_rhost flag is enabled. On Linux systems,
enabling pam_rhost may result in DNS lookups of the local
host name when PAM is initialized. On Solaris versions
prior to Solaris 8, pam_rhost must be enabled if
pam_ruser is also enabled to avoid a crash in the Solaris
PAM implementation.
This flag is off by default on systems other than
Solaris.
This setting is only supported by version 1.9.0 or
higher.
pam_ruser On systems that use PAM for authentication, sudo will set
the PAM remote user value to the name of the user that
invoked sudo when the pam_ruser flag is enabled. This
flag is on by default.
This setting is only supported by version 1.9.0 or
higher.
pam_session On systems that use PAM for authentication, sudo will
create a new PAM session for the command to be run in.
Unless sudo is given the -i or -s options, PAM session
modules are run with the "silent" flag enabled. This
prevents last login information from being displayed for
every command on some systems. Disabling pam_session may
be needed on older PAM implementations or on operating
systems where opening a PAM session changes the utmp or
wtmp files. If PAM session support is disabled, resource
limits may not be updated for the command being run. If
pam_session, pam_setcred, and use_pty are disabled,
log_servers has not been set and I/O logging has not been
configured, sudo will execute the command directly
instead of running it as a child process. This flag is
on by default.
This setting is only supported by version 1.8.7 or
higher.
pam_setcred On systems that use PAM for authentication, sudo will
attempt to establish credentials for the target user by
default, if supported by the underlying authentication
system. One example of a credential is a Kerberos
ticket. If pam_session, pam_setcred, and use_pty are
disabled, log_servers has not been set and I/O logging
has not been configured, sudo will execute the command
directly instead of running it as a child process. This
flag is on by default.
This setting is only supported by version 1.8.8 or
higher.
passprompt_override
If set, the prompt specified by passprompt or the
SUDO_PROMPT environment variable will always be used and
will replace the prompt provided by a PAM module or other
authentication method. This flag is off by default.
path_info Normally, sudo will tell the user when a command could
not be found in their PATH environment variable. Some
sites may wish to disable this as it could be used to
gather information on the location of executables that
the normal user does not have access to. The
disadvantage is that if the executable is simply not in
the user's PATH, sudo will tell the user that they are
not allowed to run it, which can be confusing. This flag
is on by default.
preserve_groups By default, sudo will initialize the group vector to the
list of groups the target user is in. When
preserve_groups is set, the user's existing group vector
is left unaltered. The real and effective group-IDs,
however, are still set to match the target user. This
flag is off by default.
pwfeedback By default, sudo reads the password like most other Unix
programs, by turning off echo until the user hits the
return (or enter) key. Some users become confused by
this as it appears to them that sudo has hung at this
point. When pwfeedback is set, sudo will provide visual
feedback when the user presses a key. This does have a
security impact as an onlooker may be able to determine
the length of the password being entered. This flag is
off by default.
requiretty If set, sudo will only run when the user is logged in to
a real tty. When this flag is set, sudo can only be run
from a login session and not via other means such as
cron(8) or cgi-bin scripts. This flag is off by default.
root_sudo If set, root is allowed to run sudo too. Disabling this
prevents users from "chaining" sudo commands to get a
root shell by doing something like `sudo sudo /bin/sh'.
Note, however, that turning off root_sudo will also
prevent root from running sudoedit. Disabling root_sudo
provides no real additional security; it exists purely
for historical reasons. This flag is on by default.
rootpw If set, sudo will prompt for the root password instead of
the password of the invoking user when running a command
or editing a file. This flag is off by default.
runas_allow_unknown_id
If enabled, allow matching of runas user and group IDs
that are not present in the password or group databases.
In addition to explicitly matching unknown user or group
IDs in a Runas_List, this option also allows the ALL
alias to match unknown IDs. This flag is off by default.
This setting is only supported by version 1.8.30 or
higher. Older versions of sudo always allowed matching
of unknown user and group IDs.
runas_check_shell
If enabled, sudo will only run commands as a user whose
shell appears in the /etc/shells file, even if the
invoking user's Runas_List would otherwise permit it. If
no /etc/shells file is present, a system-dependent list
of built-in default shells is used. On many operating
systems, system users such as "bin", do not have a valid
shell and this flag can be used to prevent commands from
being run as those users. This flag is off by default.
This setting is only supported by version 1.8.30 or
higher.
runaspw If set, sudo will prompt for the password of the user
defined by the runas_default option (defaults to root)
instead of the password of the invoking user when running
a command or editing a file. This flag is off by
default.
set_home If enabled and sudo is invoked with the -s option, the
HOME environment variable will be set to the home
directory of the target user (which is the runas_default
user unless the -u option is used). This flag is largely
obsolete and has no effect unless the env_reset flag has
been disabled or HOME is present in the env_keep list,
both of which are strongly discouraged. This flag is off
by default.
set_logname Normally, sudo will set the LOGNAME and USER environment
variables to the name of the target user (the user
specified by runas_default unless the -u option is
given). However, since some programs (including the RCS
revision control system) use LOGNAME to determine the
real identity of the user, it may be desirable to change
this behavior. This can be done by negating the
set_logname option. The set_logname option will have no
effect if the env_reset option has not been disabled and
the env_keep list contains LOGNAME or USER. This flag is
on by default.
set_utmp When enabled, sudo will create an entry in the utmp (or
utmpx) file when a pseudo-terminal is allocated. A
pseudo-terminal is allocated by sudo when it is running
in a terminal and one or more of the log_input,
log_output, log_stdin, log_stdout, log_stderr, log_ttyin,
log_ttyout, or use_pty flags is enabled. By default, the
new entry will be a copy of the user's existing utmp
entry (if any), with the tty, time, type, and pid fields
updated. This flag is on by default.
setenv Allow the user to disable the env_reset option from the
command line via the -E option. Additionally,
environment variables set via the command line are not
subject to the restrictions imposed by env_check,
env_delete, or env_keep. As such, only trusted users
should be allowed to set variables in this manner. This
flag is off by default.
shell_noargs If set and sudo is invoked with no arguments it acts as
if the -s option had been given. That is, it runs a
shell as root (the shell is determined by the SHELL
environment variable if it is set, falling back on the
shell listed in the invoking user's /etc/passwd entry if
not). This flag is off by default.
stay_setuid Normally, when sudo executes a command the real and
effective user-IDs are set to the target user (root by
default). This option changes that behavior such that
the real user-ID is left as the invoking user's user-ID.
In other words, this makes sudo act as a set-user-ID
wrapper. This can be useful on systems that disable some
potentially dangerous functionality when a program is run
set-user-ID. This option is only effective on systems
that support either the setreuid(2) or setresuid(2)
system call. This flag is off by default.
sudoedit_checkdir
If set, sudoedit will check all directory components of
the path to be edited for writability by the invoking
user. Symbolic links will not be followed in writable
directories and sudoedit will refuse to edit a file
located in a writable directory. These restrictions are
not enforced when sudoedit is run by root. On some
systems, if all directory components of the path to be
edited are not readable by the target user, sudoedit will
be unable to edit the file. This flag is on by default.
This setting was first introduced in version 1.8.15 but
initially suffered from a race condition. The check for
symbolic links in writable intermediate directories was
added in version 1.8.16.
sudoedit_follow By default, sudoedit will not follow symbolic links when
opening files. The sudoedit_follow option can be enabled
to allow sudoedit to open symbolic links. It may be
overridden on a per-command basis by the FOLLOW and
NOFOLLOW tags. This flag is off by default.
This setting is only supported by version 1.8.15 or
higher.
syslog_pid When logging via syslog(3), include the process ID in the
log entry. This flag is off by default.
This setting is only supported by version 1.8.21 or
higher.
targetpw If set, sudo will prompt for the password of the user
specified by the -u option (defaults to the value of
runas_default) instead of the password of the invoking
user when running a command or editing a file. This flag
precludes the use of a user-ID not listed in the passwd
database as an argument to the -u option. This flag is
off by default.
tty_tickets If set, users must authenticate on a per-tty basis. With
this flag enabled, sudo will use a separate record in the
time stamp file for each terminal. If disabled, a single
record is used for all login sessions.
This option has been superseded by the timestamp_type
option.
umask_override If set, sudo will set the umask as specified in the
sudoers file without modification. This makes it
possible to specify a umask in the sudoers file that is
more permissive than the user's own umask and matches
historical behavior. If umask_override is not set, sudo
will set the umask to be the union of the user's umask
and what is specified in sudoers. This flag is off by
default.
use_netgroups If set, netgroups (prefixed with `+'), may be used in
place of a user or host. For LDAP-based sudoers,
netgroup support requires an expensive sub-string match
on the server unless the NETGROUP_BASE directive is
present in the /etc/ldap.conf file. If netgroups are not
needed, this option can be disabled to reduce the load on
the LDAP server. This flag is on by default.
use_pty If set, and sudo is running in a terminal, the command
will be run in a pseudo-terminal (even if no I/O logging
is being done). If the sudo process is not attached to a
terminal, use_pty has no effect.
A malicious program run under sudo may be capable of
injecting commands into the user's terminal or running a
background process that retains access to the user's
terminal device even after the main program has finished
executing. By running the command in a separate pseudo-
terminal, this attack is no longer possible. This flag
is off by default.
user_command_timeouts
If set, the user may specify a timeout on the command
line. If the timeout expires before the command has
exited, the command will be terminated. If a timeout is
specified both in the sudoers file and on the command
line, the smaller of the two timeouts will be used. See
the Timeout_Spec section for a description of the timeout
syntax. This flag is off by default.
This setting is only supported by version 1.8.20 or
higher.
utmp_runas If set, sudo will store the name of the runas user when
updating the utmp (or utmpx) file. By default, sudo
stores the name of the invoking user. This flag is off
by default.
visiblepw By default, sudo will refuse to run if the user must
enter a password but it is not possible to disable echo
on the terminal. If the visiblepw flag is set, sudo will
prompt for a password even when it would be visible on
the screen. This makes it possible to run things like
`ssh somehost sudo ls' since by default, ssh(1) does not
allocate a tty when running a command. This flag is off
by default.
Integers:
closefrom Before it executes a command, sudo will close all open
file descriptors other than standard input, standard
output, and standard error (file descriptors 0-2). The
closefrom option can be used to specify a different file
descriptor at which to start closing. The default is 3.
command_timeout The maximum amount of time a command is allowed to run
before it is terminated. See the Timeout_Spec section
for a description of the timeout syntax.
This setting is only supported by version 1.8.20 or
higher.
log_server_timeout
The maximum amount of time to wait when connecting to a
log server or waiting for a server response. See the
Timeout_Spec section for a description of the timeout
syntax. The default value is 30 seconds.
This setting is only supported by version 1.9.0 or
higher.
maxseq The maximum sequence number that will be substituted for
the `%{seq}' escape in the I/O log file (see the
iolog_dir description below for more information). While
the value substituted for `%{seq}' is in base 36, maxseq
itself should be expressed in decimal. Values larger
than 2176782336 (which corresponds to the base 36
sequence number "ZZZZZZ") will be silently truncated to
2176782336. The default value is 2176782336.
Once the local sequence number reaches the value of
maxseq, it will "roll over" to zero, after which sudoers
will truncate and re-use any existing I/O log path names.
This setting is only supported by version 1.8.7 or
higher.
passwd_tries The number of tries a user gets to enter his/her password
before sudo logs the failure and exits. The default is
3.
syslog_maxlen On many systems, syslog(3) has a relatively small log
buffer. IETF RFC 5424 states that syslog servers must
support messages of at least 480 bytes and should support
messages up to 2048 bytes. By default, sudoers creates
log messages up to 980 bytes which corresponds to the
historic BSD syslog implementation which used a 1024 byte
buffer to store the message, date, hostname, and program
name. To prevent syslog messages from being truncated,
sudoers will split up log messages that are larger than
syslog_maxlen bytes. When a message is split, additional
parts will include the string "(command continued)" after
the user name and before the continued command line
arguments.
This setting is only supported by version 1.8.19 or
higher.
Integers that can be used in a boolean context:
loglinelen Number of characters per line for the file log. This
value is used to decide when to wrap lines for nicer log
files. This has no effect on the syslog log file, only
the file log. The default is 80 (use 0 or negate the
option to disable word wrap).
passwd_timeout Number of minutes before the sudo password prompt times
out, or 0 for no timeout. The timeout may include a
fractional component if minute granularity is
insufficient, for example 2.5. The default is 0.
timestamp_timeout
Number of minutes that can elapse before sudo will ask
for a password again. The timeout may include a
fractional component if minute granularity is
insufficient, for example 2.5. The default is 5. Set
this to 0 to always prompt for a password. If set to a
value less than 0 the user's time stamp will not expire
until the system is rebooted. This can be used to allow
users to create or delete their own time stamps via `sudo
-v' and `sudo -k' respectively.
umask File mode creation mask to use when running the command.
Negate this option or set it to 0777 to prevent sudoers
from changing the umask. Unless the umask_override flag
is set, the actual umask will be the union of the user's
umask and the value of the umask setting, which defaults
to 0022. This guarantees that sudo never lowers the
umask when running a command.
If umask is explicitly set in sudoers, it will override
any umask setting in PAM or login.conf. If umask is not
set in sudoers, the umask specified by PAM or login.conf
will take precedence. The umask setting in PAM is not
used for sudoedit, which does not create a new PAM
session.
Strings:
authfail_message Message that is displayed after a user fails to
authenticate. The message may include the `%d' escape
which will expand to the number of failed password
attempts. If set, it overrides the default message, "%d
incorrect password attempt(s)".
badpass_message Message that is displayed if a user enters an incorrect
password. The default is "Sorry, try again." unless
insults are enabled.
editor A colon (`:') separated list of editor path names used by
sudoedit and visudo. For sudoedit, this list is used to
find an editor when none of the SUDO_EDITOR, VISUAL or
EDITOR environment variables are set to an editor that
exists and is executable. For visudo, it is used as a
white list of allowed editors; visudo will choose the
editor that matches the user's SUDO_EDITOR, VISUAL or
EDITOR environment variable if possible, or the first
editor in the list that exists and is executable if not.
Unless invoked as sudoedit, sudo does not preserve the
SUDO_EDITOR, VISUAL or EDITOR environment variables
unless they are present in the env_keep list or the
env_reset option is disabled. The default is
/usr/bin/vi.
intercept_type The underlying mechanism used by the intercept and
log_subcmds options. It has the following possible
values:
dso Preload a dynamic shared object (shared library)
that intercepts the execve(2), execl(3),
execle(3), execlp(3), execv(3), execvp(3),
execvpe(3), and system(3) library functions. A
value of dso is incompatible with sudo's SELinux
RBAC support.
trace Use ptrace(2) to intercept the execve(2) system
call. This is only supported on Linux systems
where seccomp(2) filtering is enabled. If the
/proc/sys/kernel/seccomp/actions_avail file is
missing or does not contain a "trap" element,
setting intercept_type to trace will have no
effect and dso will be used instead.
The default is to use trace if it is supported by the
system and dso if it is not.
iolog_dir The top-level directory to use when constructing the path
name for the input/output log directory. Only used if
the log_input or log_output options are enabled or when
the LOG_INPUT or LOG_OUTPUT tags are present for a
command. The session sequence number, if any, is stored
in the directory. The default is /var/log/sudo-io.
The following percent (`%') escape sequences are
supported:
%{seq}
expanded to a monotonically increasing base-36
sequence number, such as 0100A5, where every two
digits are used to form a new directory, e.g.,
01/00/A5
%{user}
expanded to the invoking user's login name
%{group}
expanded to the name of the invoking user's real
group-ID
%{runas_user}
expanded to the login name of the user the command
will be run as (e.g., root)
%{runas_group}
expanded to the group name of the user the command
will be run as (e.g., wheel)
%{hostname}
expanded to the local host name without the domain
name
%{command}
expanded to the base name of the command being run
In addition, any escape sequences supported by the
system's strftime(3) function will be expanded.
To include a literal `%' character, the string `%%'
should be used.
iolog_file The path name, relative to iolog_dir, in which to store
input/output logs when the log_input or log_output
options are enabled or when the LOG_INPUT or LOG_OUTPUT
tags are present for a command. iolog_file may contain
directory components. The default is `%{seq}'.
See the iolog_dir option above for a list of supported
percent (`%') escape sequences.
In addition to the escape sequences, path names that end
in six or more Xs will have the Xs replaced with a unique
combination of digits and letters, similar to the
mktemp(3) function.
If the path created by concatenating iolog_dir and
iolog_file already exists, the existing I/O log file will
be truncated and overwritten unless iolog_file ends in
six or more Xs.
iolog_flush If set, sudo will flush I/O log data to disk after each
write instead of buffering it. This makes it possible to
view the logs in real-time as the program is executing
but may significantly reduce the effectiveness of I/O log
compression. This flag is off by default.
This setting is only supported by version 1.8.20 or
higher.
iolog_group The group name to look up when setting the group-ID on
new I/O log files and directories. If iolog_group is not
set, the primary group-ID of the user specified by
iolog_user is used. If neither iolog_group nor
iolog_user are set, I/O log files and directories are
created with group-ID 0.
This setting is only supported by version 1.8.19 or
higher.
iolog_mode The file mode to use when creating I/O log files. Mode
bits for read and write permissions for owner, group, or
other are honored, everything else is ignored. The file
permissions will always include the owner read and write
bits, even if they are not present in the specified mode.
When creating I/O log directories, search (execute) bits
are added to match the read and write bits specified by
iolog_mode. Defaults to 0600 (read and write by user
only).
This setting is only supported by version 1.8.19 or
higher.
iolog_user The user name to look up when setting the user and group-
IDs on new I/O log files and directories. If iolog_group
is set, it will be used instead of the user's primary
group-ID. By default, I/O log files and directories are
created with user and group-ID 0.
This setting can be useful when the I/O logs are stored
on a Network File System (NFS) share. Having a dedicated
user own the I/O log files means that sudoers does not
write to the log files as user-ID 0, which is usually not
permitted by NFS.
This setting is only supported by version 1.8.19 or
higher.
lecture_status_dir
The directory in which sudo stores per-user lecture
status files. Once a user has received the lecture, a
zero-length file is created in this directory so that
sudo will not lecture the user again. This directory
should not be cleared when the system reboots. The
default is /var/db/sudo/lectured.
log_server_cabundle
The path to a certificate authority bundle file, in PEM
format, to use instead of the system's default
certificate authority database when authenticating the
log server. The default is to use the system's default
certificate authority database. This setting has no
effect unless log_servers is set and the remote log
server is secured with TLS.
This setting is only supported by version 1.9.0 or
higher.
log_server_peer_cert
The path to the sudo client's certificate file, in PEM
format. This setting is required when the remote log
server is secured with TLS and client certificate
validation is enabled. For sudo_logsrvd, client
certificate validation is controlled by the tls_checkpeer
option, which defaults to false.
This setting is only supported by version 1.9.0 or
higher.
log_server_peer_key
The path to the sudo client's private key file, in PEM
format. This setting is required when the remote log
server is secured with TLS and client certificate
validation is enabled. For sudo_logsrvd, client
certificate validation is controlled by the tls_checkpeer
flag, which defaults to false.
This setting is only supported by version 1.9.0 or
higher.
mailsub Subject of the mail sent to the mailto user. The escape
`%h' will expand to the host name of the machine.
Default is "*** SECURITY information for %h ***".
noexec_file As of sudo version 1.8.1 this option is no longer
supported. The path to the noexec file should now be set
in the sudo.conf(5) file.
pam_askpass_service
On systems that use PAM for authentication, this is the
service name used when the -A option is specified. The
default value is either `sudo' or `sudo', depending on
whether or not the -i option is also specified. See the
description of pam_service for more information.
This setting is only supported by version 1.9.9 or
higher.
pam_login_service
On systems that use PAM for authentication, this is the
service name used when the -i option is specified. The
default value is `sudo'. See the description of
pam_service for more information.
This setting is only supported by version 1.8.8 or
higher.
pam_service On systems that use PAM for authentication, the service
name specifies the PAM policy to apply. This usually
corresponds to an entry in the pam.conf file or a file in
the /etc/pam.d directory. The default value is `sudo'.
This setting is only supported by version 1.8.8 or
higher.
passprompt The default prompt to use when asking for a password; can
be overridden via the -p option or the SUDO_PROMPT
environment variable. The following percent (`%') escape
sequences are supported:
%H expanded to the local host name including the
domain name (only if the machine's host name is
fully qualified or the fqdn option is set)
%h expanded to the local host name without the domain
name
%p expanded to the user whose password is being asked
for (respects the rootpw, targetpw and runaspw
flags in sudoers)
%U expanded to the login name of the user the command
will be run as (defaults to root)
%u expanded to the invoking user's login name
%% two consecutive `%' characters are collapsed into a
single `%' character
On systems that use PAM for authentication, passprompt
will only be used if the prompt provided by the PAM
module matches the string "Password: " or "username's
Password: ". This ensures that the passprompt setting
does not interfere with challenge-response style
authentication. The passprompt_override flag can be used
to change this behavior.
The default value is `Password: '.
runas_default The default user to run commands as if the -u option is
not specified on the command line. This defaults to
root.
sudoers_locale Locale to use when parsing the sudoers file, logging
commands, and sending email. Changing the locale may
affect how sudoers is interpreted. Defaults to `C'.
timestamp_type sudoers uses per-user time stamp files for credential
caching. The timestamp_type option can be used to
specify the type of time stamp record used. It has the
following possible values:
global A single time stamp record is used for all of a
user's login sessions, regardless of the terminal
or parent process ID. An additional record is
used to serialize password prompts when sudo is
used multiple times in a pipeline, but this does
not affect authentication.
ppid A single time stamp record is used for all
processes with the same parent process ID
(usually the shell). Commands run from the same
shell (or other common parent process) will not
require a password for timestamp_timeout minutes
(5 by default). Commands run via sudo with a
different parent process ID, for example from a
shell script, will be authenticated separately.
tty One time stamp record is used for each terminal,
which means that a user's login sessions are
authenticated separately. If no terminal is
present, the behavior is the same as ppid.
Commands run from the same terminal will not
require a password for timestamp_timeout minutes
(5 by default).
kernel The time stamp is stored in the kernel as an
attribute of the terminal device. If no terminal
is present, the behavior is the same as ppid.
Negative timestamp_timeout values are not
supported and positive values are limited to a
maximum of 60 minutes. This is currently only
supported on OpenBSD.
The default value is tty.
This setting is only supported by version 1.8.21 or
higher.
timestampdir The directory in which sudo stores its time stamp files.
This directory should be cleared when the system reboots.
The default is /opt/local/var/run/sudo/ts.
timestampowner The owner of the lecture status directory, time stamp
directory and all files stored therein. The default is
root.
Strings that can be used in a boolean context:
admin_flag The admin_flag option specifies the path to a file that is
created the first time a user that is a member of the sudo or
admin groups runs sudo. Only available if sudo is configured
with the --enable-admin-flag option. The default value is
~/.sudo_as_admin_successful.
env_file The env_file option specifies the fully qualified path to a
file containing variables to be set in the environment of the
program being run. Entries in this file should either be of
the form `VARIABLE=value' or `export VARIABLE=value'. The
value may optionally be enclosed in single or double quotes.
Variables in this file are only added if the variable does
not already exist in the environment. This file is
considered to be part of the security policy, its contents
are not subject to other sudo environment restrictions such
as env_keep and env_check.
exempt_group Users in this group are exempt from password and PATH
requirements. The group name specified should not include a
`%' prefix. This is not set by default.
fdexec Determines whether sudo will execute a command by its path or
by an open file descriptor. It has the following possible
values:
always Always execute by file descriptor.
never Never execute by file descriptor.
digest_only
Only execute by file descriptor if the command has an
associated digest in the sudoers file.
The default value is digest_only. This avoids a time of
check versus time of use race condition when the command is
located in a directory writable by the invoking user.
fdexec will change the first element of the argument vector
for scripts ($0 in the shell) due to the way the kernel runs
script interpreters. Instead of being a normal path, it will
refer to a file descriptor. For example, /dev/fd/4 on
Solaris and /proc/self/fd/4 on Linux. A workaround is to use
the SUDO_COMMAND environment variable instead.
The fdexec setting is only used when the command is matched
by path name. It has no effect if the command is matched by
the built-in ALL alias.
This setting is only supported by version 1.8.20 or higher.
If the operating system does not support the fexecve(2)
system call, this setting has no effect.
group_plugin A string containing a sudoers group plugin with optional
arguments. The string should consist of the plugin path,
either fully-qualified or relative to the
/opt/local/libexec/sudo directory, followed by any
configuration arguments the plugin requires. These arguments
(if any) will be passed to the plugin's initialization
function. If arguments are present, the string must be
enclosed in double quotes ("").
On 64-bit systems, if the plugin is present but cannot be
loaded, sudoers will look for a 64-bit version and, if it
exists, load that as a fallback. The exact rules for this
vary by system. On Solaris, if the plugin is stored in a
directory ending in "lib", sudoers will create a fallback
path by appending "/64" to the directory name;
/opt/local/lib/group_plugin.so becomes
/opt/local/lib/64/group_plugin.so. On Linux, a directory
ending in "lib" will be transformed to "lib64" as the
fallback path; /opt/local/lib/group_plugin.so becomes
/opt/local/lib64/group_plugin.so. On all other systems, the
fallback path is generated by adding a "64" before the file
extension; group_plugin.so becomes group_plugin64.so.
For more information see GROUP PROVIDER PLUGINS.
lecture This option controls when a short lecture will be printed
along with the password prompt. It has the following
possible values:
always Always lecture the user.
never Never lecture the user.
once Only lecture the user the first time they run sudo.
If no value is specified, a value of once is implied.
Negating the option results in a value of never being used.
The default value is once.
lecture_file Path to a file containing an alternate sudo lecture that will
be used in place of the standard lecture if the named file
exists. By default, sudo uses a built-in lecture.
listpw This option controls when a password will be required when a
user runs sudo with the -l option. It has the following
possible values:
all All the user's sudoers file entries for the current
host must have the NOPASSWD flag set to avoid entering
a password.
always
The user must always enter a password to use the -l
option.
any At least one of the user's sudoers file entries for the
current host must have the NOPASSWD flag set to avoid
entering a password.
never
The user need never enter a password to use the -l
option.
If no value is specified, a value of any is implied.
Negating the option results in a value of never being used.
The default value is any.
log_format The event log format. Supported log formats are:
json Logs in JSON format. JSON log entries contain the full
user details as well as the execution environment if
the command was allowed. Due to limitations of the
protocol, JSON events sent via syslog may be truncated.
sudo Traditional sudo-style logs, see EVENT LOGGING for a
description of the log file format.
This setting affects logs sent via syslog(3) as well as the
file specified by the logfile setting, if any. The default
value is sudo.
logfile Path to the sudo log file (not the syslog log file). Setting
a path turns on logging to a file; negating this option turns
it off. By default, sudo logs via syslog.
mailerflags Flags to use when invoking mailer. Defaults to -t.
mailerpath Path to mail program used to send warning mail (negate to
prevent sudo from sending mail). Defaults to the path to
sendmail found at configure time.
mailfrom Address to use for the "from" address when sending warning
and error mail. The address should be enclosed in double
quotes ("") to protect against sudo interpreting the `@'
sign. Defaults to the name of the user running sudo.
mailto Address to send warning and error mail to (negate to prevent
sudo from sending mail). The address should be enclosed in
double quotes ("") to protect against sudo interpreting the
`@' sign. Defaults to root.
rlimit_as The maximum size to which the process's address space may
grow (in bytes), if supported by the operating system. See
Resource limits for more information.
rlimit_core The largest size core dump file that may be created (in
bytes). See Resource limits for more information. Defaults
to 0 (no core dump created).
rlimit_cpu The maximum amount of CPU time that the process may use (in
seconds). See Resource limits for more information.
rlimit_data The maximum size of the data segment for the process (in
bytes). See Resource limits for more information.
rlimit_fsize The largest size file that the process may create (in bytes).
See Resource limits for more information.
rlimit_locks The maximum number of locks that the process may establish,
if supported by the operating system. See Resource limits
for more information.
rlimit_memlock
The maximum size that the process may lock in memory (in
bytes), if supported by the operating system. See Resource
limits for more information.
rlimit_nofile
The maximum number of files that the process may have open.
See Resource limits for more information.
rlimit_nproc The maximum number of processes that the user may run
simultaneously. See Resource limits for more information.
rlimit_rss The maximum size to which the process's resident set size may
grow (in bytes). See Resource limits for more information.
rlimit_stack The maximum size to which the process's stack may grow (in
bytes). See Resource limits for more information.
restricted_env_file
The restricted_env_file option specifies the fully qualified
path to a file containing variables to be set in the
environment of the program being run. Entries in this file
should either be of the form `VARIABLE=value' or `export
VARIABLE=value'. The value may optionally be enclosed in
single or double quotes. Variables in this file are only
added if the variable does not already exist in the
environment. Unlike env_file, the file's contents are not
trusted and are processed in a manner similar to that of the
invoking user's environment. If env_reset is enabled,
variables in the file will only be added if they are matched
by either the env_check or env_keep list. If env_reset is
disabled, variables in the file are added as long as they are
not matched by the env_delete list. In either case, the
contents of restricted_env_file are processed before the
contents of env_file.
runchroot If set, sudo will use this value for the root directory when
running a command. The special value "*" will allow the user
to specify the root directory via sudo's -R option. See the
Chroot_Spec section for more details.
It is only possible to use runchroot as a command-specific
Defaults setting if the command exists with the same path
both inside and outside the chroot jail. This restriction
does not apply to global, host, or user-based Defaults
settings or to a Cmnd_Spec that includes a Chroot_Spec.
This setting is only supported by version 1.9.3 or higher.
runcwd If set, sudo will use this value for the working directory
when running a command. The special value "*" will allow the
user to specify the working directory via sudo's -D option.
See the Chdir_Spec section for more details.
This setting is only supported by version 1.9.3 or higher.
secure_path If set, sudo will use this value in place of the user's PATH
environment variable. This option can be used to reset the
PATH to a known good value that contains directories for
system administrator commands such as /usr/sbin.
Users in the group specified by the exempt_group option are
not affected by secure_path. This option is not set by
default.
syslog Syslog facility if syslog is being used for logging (negate
to disable syslog logging). Defaults to authpriv.
The following syslog facilities are supported: authpriv (if
your OS supports it), auth, daemon, user, local0, local1,
local2, local3, local4, local5, local6, and local7.
syslog_badpri
Syslog priority to use when the user is not allowed to run a
command or when authentication is unsuccessful. Defaults to
alert.
The following syslog priorities are supported: alert, crit,
debug, emerg, err, info, notice, warning, and none. Negating
the option or setting it to a value of none will disable
logging of unsuccessful commands.
syslog_goodpri
Syslog priority to use when the user is allowed to run a
command and authentication is successful. Defaults to
notice.
See syslog_badpri for the list of supported syslog
priorities. Negating the option or setting it to a value of
none will disable logging of successful commands.
verifypw This option controls when a password will be required when a
user runs sudo with the -v option. It has the following
possible values:
all All the user's sudoers file entries for the current
host must have the NOPASSWD flag set to avoid
entering a password.
always The user must always enter a password to use the -v
option.
any At least one of the user's sudoers file entries for
the current host must have the NOPASSWD flag set to
avoid entering a password.
never The user need never enter a password to use the -v
option.
If no value is specified, a value of all is implied.
Negating the option results in a value of never being used.
The default value is all.
Lists that can be used in a boolean context:
env_check Environment variables to be removed from the user's
environment unless they are considered "safe". For all
variables except TZ, "safe" means that the variable's
value does not contain any `%' or `/' characters. This
can be used to guard against printf-style format
vulnerabilities in poorly-written programs. The TZ
variable is considered unsafe if any of the following are
true:
o It consists of a fully-qualified path name, optionally
prefixed with a colon (`:'), that does not match the
location of the zoneinfo directory.
o It contains a .. path element.
o It contains white space or non-printable characters.
o It is longer than the value of PATH_MAX.
The argument may be a double-quoted, space-separated list
or a single value without double-quotes. The list can be
replaced, added to, deleted from, or disabled by using
the `=', `+=', `-=', and `!' operators respectively.
Regardless of whether the env_reset option is enabled or
disabled, variables specified by env_check will be
preserved in the environment if they pass the
aforementioned check. The global list of environment
variables to check is displayed when sudo is run by root
with the -V option.
env_delete Environment variables to be removed from the user's
environment when the env_reset option is not in effect.
The argument may be a double-quoted, space-separated list
or a single value without double-quotes. The list can be
replaced, added to, deleted from, or disabled by using
the `=', `+=', `-=', and `!' operators respectively. The
global list of environment variables to remove is
displayed when sudo is run by root with the -V option.
Many operating systems will remove potentially dangerous
variables from the environment of any set-user-ID process
(such as sudo).
env_keep Environment variables to be preserved in the user's
environment when the env_reset option is in effect. This
allows fine-grained control over the environment
sudo-spawned processes will receive. The argument may be
a double-quoted, space-separated list or a single value
without double-quotes. The list can be replaced, added
to, deleted from, or disabled by using the `=', `+=',
`-=', and `!' operators respectively. The global list of
variables to keep is displayed when sudo is run by root
with the -V option.
Preserving the HOME environment variable has security
implications since many programs use it when searching
for configuration or data files. Adding HOME to env_keep
may enable a user to run unrestricted commands via sudo
and is strongly discouraged. Users wishing to edit files
with sudo should run sudoedit (or sudo -e) to get their
accustomed editor configuration instead of invoking the
editor directly.
log_servers A list of one or more servers to use for remote event and
I/O log storage, separated by white space. Log servers
must be running sudo_logsrvd or another service that
implements the protocol described by
sudo_logsrv.proto(5).
Server addresses should be of the form
"host[:port][(tls)]". The host portion may be a host
name, an IPv4 address, or an IPv6 address in square
brackets.
If the optional tls flag is present, the connection will
be secured with Transport Layer Security (TLS) version
1.2 or 1.3. Versions of TLS prior to 1.2 are not
supported.
If a port is specified, it may either be a port number or
a well-known service name as defined by the system
service name database. If no port is specified, port
30343 will be used for plaintext connections and port
30344 will be used for TLS connections.
When log_servers is set, event log data will be logged
both locally (see the syslog and log_file settings) as
well as remotely, but I/O log data will only be logged
remotely. If multiple hosts are specified, they will be
attempted in reverse order. If no log servers are
available, the user will not be able to run a command
unless either the ignore_iolog_errors flag (I/O logging
enabled) or the ignore_log_errors flag (I/O logging
disabled) is set. Likewise, if the connection to the log
server is interrupted while sudo is running, the command
will be terminated unless the ignore_iolog_errors flag
(I/O logging enabled) or the ignore_log_errors flag (I/O
logging disabled) is set.
This setting is only supported by version 1.9.0 or
higher.
passprompt_regex A list of POSIX extended regular expressions used to
match password prompts in the terminal output. As an
extension, if the regular expression begins with "(?i)",
it will be matched in a case-insensitive manner. Each
regular expression is limited to 1024 characters. This
option is only used when log_passwords has been disabled.
The default value is "[Pp]assword[: ]*"
This setting is only supported by version 1.9.10 or
higher.
GROUP PROVIDER PLUGINS
The sudoers plugin supports its own plugin interface to allow non-Unix
group lookups which can query a group source other than the standard Unix
group database. This can be used to implement support for the
nonunix_group syntax described earlier.
Group provider plugins are specified via the group_plugin setting. The
argument to group_plugin should consist of the plugin path, either fully-
qualified or relative to the /opt/local/libexec/sudo directory, followed by
any configuration options the plugin requires. These options (if
specified) will be passed to the plugin's initialization function. If
options are present, the string must be enclosed in double quotes ("").
The following group provider plugins are installed by default:
group_file
The group_file plugin supports an alternate group file that uses the
same syntax as the /etc/group file. The path to the group file
should be specified as an option to the plugin. For example, if the
group file to be used is /etc/sudo-group:
Defaults group_plugin="group_file.so /etc/sudo-group"
system_group
The system_group plugin supports group lookups via the standard C
library functions getgrnam(3) and getgrid(3). This plugin can be
used in instances where the user belongs to groups not present in the
user's supplemental group vector. This plugin takes no options:
Defaults group_plugin=system_group.so
The group provider plugin API is described in detail in sudo_plugin(5).
EVENT LOGGING
sudoers can log events in either JSON or sudo format, this section
describes the sudo log format. Depending on sudoers configuration, sudoers
can log events via syslog(3), to a local log file, or both. The log format
is almost identical in both cases. Any control characters present in the
log data are formatted in octal with a leading `#' character. For example,
a horizontal tab is stored as `#011' and an embedded carriage return is
stored as `#015'. In addition, space characters in the command path are
stored as `#040'. Command line arguments that contain spaces are enclosed
in single quotes (''). This makes it possible to distinguish multiple
command line arguments from a single argument that contains spaces.
Literal single quotes and backslash characters (`\') in command line
arguments are escaped with a backslash.
Accepted command log entries
Commands that sudo runs are logged using the following format (split into
multiple lines for readability):
date hostname progname: username : TTY=ttyname ; CHROOT=chroot ; \
PWD=cwd ; USER=runasuser ; GROUP=runasgroup ; TSID=logid ; \
ENV=env_vars COMMAND=command
Where the fields are as follows:
date The date the command was run. Typically, this is in the
format "MMM, DD, HH:MM:SS". If logging via syslog(3), the
actual date format is controlled by the syslog daemon. If
logging to a file and the log_year option is enabled, the
date will also include the year.
hostname The name of the host sudo was run on. This field is only
present when logging via syslog(3).
progname The name of the program, usually sudo or sudoedit. This
field is only present when logging via syslog(3).
username The login name of the user who ran sudo.
ttyname The short name of the terminal (e.g., "console", "tty01", or
"pts/0") sudo was run on, or "unknown" if there was no
terminal present.
chroot The root directory that the command was run in, if one was
specified.
cwd The current working directory that sudo was run in.
runasuser The user the command was run as.
runasgroup The group the command was run as if one was specified on the
command line.
logid An I/O log identifier that can be used to replay the
command's output. This is only present when the log_input or
log_output option is enabled.
env_vars A list of environment variables specified on the command
line, if specified.
command The actual command that was executed, including any command
line arguments.
Messages are logged using the locale specified by sudoers_locale, which
defaults to the `C' locale.
Denied command log entries
If the user is not allowed to run the command, the reason for the denial
will follow the user name. Possible reasons include:
user NOT in sudoers
The user is not listed in the sudoers file.
user NOT authorized on host
The user is listed in the sudoers file but is not allowed to run
commands on the host.
command not allowed
The user is listed in the sudoers file for the host but they are not
allowed to run the specified command.
3 incorrect password attempts
The user failed to enter their password after 3 tries. The actual
number of tries will vary based on the number of failed attempts and the
value of the passwd_tries option.
a password is required
The -n option was specified but a password was required.
sorry, you are not allowed to set the following environment variables
The user specified environment variables on the command line that were
not allowed by sudoers.
Error log entries
If an error occurs, sudoers will log a message and, in most cases, send a
message to the administrator via email. Possible errors include:
parse error in /opt/local/etc/sudoers near line N
sudoers encountered an error when parsing the specified file. In some
cases, the actual error may be one line above or below the line number
listed, depending on the type of error.
problem with defaults entries
The sudoers file contains one or more unknown Defaults settings. This
does not prevent sudo from running, but the sudoers file should be
checked using visudo.
timestamp owner (username): No such user
The time stamp directory owner, as specified by the timestampowner
setting, could not be found in the password database.
unable to open/read /opt/local/etc/sudoers
The sudoers file could not be opened for reading. This can happen when
the sudoers file is located on a remote file system that maps user-ID 0
to a different value. Normally, sudoers tries to open the sudoers file
using group permissions to avoid this problem. Consider either changing
the ownership of /opt/local/etc/sudoers or adding an argument like
"sudoers_uid=N" (where `N' is the user-ID that owns the sudoers file) to
the end of the sudoers Plugin line in the sudo.conf(5) file.
unable to open /opt/local/etc/sudoers
The /opt/local/etc/sudoers file is missing.
/opt/local/etc/sudoers is not a regular file
The /opt/local/etc/sudoers file exists but is not a regular file or
symbolic link.
/opt/local/etc/sudoers is owned by uid N, should be 0
The sudoers file has the wrong owner. If you wish to change the sudoers
file owner, add "sudoers_uid=N" (where `N' is the user-ID that owns the
sudoers file) to the sudoers Plugin line in the sudo.conf(5) file.
/opt/local/etc/sudoers is world writable
The permissions on the sudoers file allow all users to write to it. The
sudoers file must not be world-writable, the default file mode is 0440
(readable by owner and group, writable by none). The default mode may
be changed via the "sudoers_mode" option to the sudoers Plugin line in
the sudo.conf(5) file.
/opt/local/etc/sudoers is owned by gid N, should be 1
The sudoers file has the wrong group ownership. If you wish to change
the sudoers file group ownership, add "sudoers_gid=N" (where `N' is the
group-ID that owns the sudoers file) to the sudoers Plugin line in the
sudo.conf(5) file.
unable to open /opt/local/var/run/sudo/ts/username
sudoers was unable to read or create the user's time stamp file. This
can happen when timestampowner is set to a user other than root and the
mode on /opt/local/var/run/sudo is not searchable by group or other.
The default mode for /opt/local/var/run/sudo is 0711.
unable to write to /opt/local/var/run/sudo/ts/username
sudoers was unable to write to the user's time stamp file.
/opt/local/var/run/sudo/ts is owned by uid X, should be Y
The time stamp directory is owned by a user other than timestampowner.
This can occur when the value of timestampowner has been changed.
sudoers will ignore the time stamp directory until the owner is
corrected.
/opt/local/var/run/sudo/ts is group writable
The time stamp directory is group-writable; it should be writable only
by timestampowner. The default mode for the time stamp directory is
0700. sudoers will ignore the time stamp directory until the mode is
corrected.
Notes on logging via syslog
By default, sudoers logs messages via syslog(3). The date, hostname, and
progname fields are added by the system's syslog(3) function, not sudoers
itself. As such, they may vary in format on different systems.
The maximum size of syslog messages varies from system to system. The
syslog_maxlen setting can be used to change the maximum syslog message size
from the default value of 980 bytes. For more information, see the
description of syslog_maxlen.
Notes on logging to a file
If the logfile option is set, sudoers will log to a local file, such as
/var/log/sudo. When logging to a file, sudoers uses a format similar to
syslog(3), with a few important differences:
1. The progname field is not present.
2. The hostname is only logged if the log_host option is enabled.
3. The date does not include the year unless the log_year option is
enabled.
4. Lines that are longer than loglinelen characters (80 by default) are
word-wrapped and continued on the next line with a four character
indent. This makes entries easier to read for a human being, but
makes it more difficult to use grep(1) on the log files. If the
loglinelen option is set to 0 (or negated with a `!'), word wrap will
be disabled.
I/O LOGGING
When I/O logging is enabled, sudo will runs the command in a pseudo-
terminal, logging user input and/or output, depending on which sudoers
flags are enabled. There are five distinct types of I/O that can be
logged, each with a corresponding sudoers flag.
Type Flag Description
terminal input log_ttyin keystrokes entered by the user
terminal output log_ttyout command output displayed to the screen
standard input log_stdin input from a pipe or a file
standard output log_stdout output to a pipe or a file
standard error log_stderr output to a pipe or a file
In addition to flags described the above, the log_input flag and LOG_INPUT
command tag set both log_ttyin and log_stdin. The log_output flag and
LOG_OUTPUT command tag set log_ttyout, log_stdout, and log_stderr.
To capture terminal input and output, sudo run the command in a pseudo-
terminal, logging the input and output before passing it on to the user.
To capture the standard input, standard output or standard error, sudo uses
a pipe to interpose itself between the input or output stream, logging the
I/O before passing it to the other end of the pipe.
I/O can be logged either to the local machine or to a remote log server.
For local logs, I/O is logged to the directory specified by the iolog_dir
option (/var/log/sudo-io by default) using a unique session ID that is
included in the sudo log line, prefixed with `TSID='. The iolog_file
option may be used to control the format of the session ID. For remote
logs, the log_servers setting is used to specify one or more log servers
running sudo_logsrvd or another server that implements the protocol
described by sudo_logsrv.proto(5).
I/O logging pitfals
When logging standard input, anything sent to the standard input will be
consumed, regardless of whether or not the command run via sudo is actively
reading the standard input. This may have unexpected results when using
sudo in a shell script that expects to process the standard input. For
example, given the following shell script:
#!/bin/sh
sudo echo testing
echo done
It will behave as expected when the script is passed to the shell as a an
argument:
$ sh test.sh
testing
done
However, if the script is passed to the shell on the standard input, the
`sudo echo testing' command will consume the rest of the script. This
means that the `echo done' statement is never executed.
$ sh -s < test.sh
testing
There are several ways to work around this problem:
1. Redirect the standard input from /dev/null when running a command via
sudo that does not need to read the standard input.
sudo echo testing < /dev/null
2. Pass the script to the shell by path name instead of via the standard
input.
sh test.sh
3. Disable logging the standard input for commands that do not need to
read the standard input.
Defaults!/bin/echo !log_stdin
Depending on the command, it may not be desirable to log the standard input
or standard output. For example, I/O logging of commands that send or
receive large amount of data via the standard output or standard input such
as rsync(1) and tar(1) could fill up the log file system with superfluous
data. It is possible to disable logging of the standard input and standard
output for such commands as follows:
Cmnd_Alias COPY_CMDS = /usr/bin/tar, /usr/bin/cpio, /usr/bin/rsync
# Log input and output but omit stdin and stdout when copying files.
Defaults log_input, log_output
Defaults!COPY_CMDS !log_stdin, !log_stdout
However, be aware that using the log_input flag or the LOG_INPUT command
tag will also enable log_stdin. Likewise, the log_ouput flag or the
LOG_OUTPUT command tag will enable log_stdout and log_stderr. Careful
ordering of rules may be necessary to achieve the results that you expect.
I/O log format
For both local and remote I/O logs, each log is stored in a separate
directory that contains the following files:
log A text file containing information about the command. The first
line consists of the following colon-delimited fields: the time
the command was run, the name of the user who ran sudo, the name
of the target user, the name of the target group (optional), the
terminal that sudo was run from, and the number of lines and
columns of the terminal. The second and third lines contain the
working directory the command was run from and the path name of
the command itself (with arguments if present).
log.json A JSON-formatted file containing information about the command.
This is similar to the log file but contains additional
information and is easily extensible. The log.json file will be
used by sudoreplay(8) in preference to the log file if it exists.
The file may contain the following elements:
timestamp
A JSON object containing time the command was run. It
consists of two values, seconds and nanoseconds.
columns
The number of columns of the terminal the command ran on,
or zero if no terminal was present.
command
The fully-qualified path of the command that was run.
lines
The number of lines of the terminal the command ran on, or
zero if no terminal was present.
runargv
A JSON array representing the command's argument vector as
passed to the execve(2) system call.
runenv
A JSON array representing the command's environment as
passed to the execve(2) system call.
rungid
The group ID the command ran as. This element is only
present when the user specifies a group on the command
line.
rungroup
The name of the group the command ran as. This element is
only present when the user specifies a group on the command
line.
runuid
The user ID the command ran as.
runuser
The name of the user the command ran as.
submitcwd
The current working directory at the time sudo was run.
submithost
The name of the host the command was run on.
submituser
The name of the user who ran the command via sudo.
ttyname
The path name of the terminal the user invoked sudo from.
If the command was run in a pseudo-terminal, ttyname will
be different from the terminal the command actually ran in.
timing Timing information used to replay the session. Each line
consists of the I/O log entry type and amount of time since the
last entry, followed by type-specific data. The I/O log entry
types and their corresponding type-specific data are:
0 standard input, number of bytes in the entry
1 standard output, number of bytes in the entry
2 standard error, number of bytes in the entry
3 terminal input, number of bytes in the entry
4 terminal output, number of bytes in the entry
5 window change, new number lines and columns
6 bug compatibility for sudo 1.8.7 terminal output
7 command suspend or resume, signal received
ttyin Raw input from the user's terminal, exactly as it was received.
This file is only present if the log_input or log_ttyin flags are
set and sudo was run from a terminal. No post-processing is
performed. For manual viewing, you may wish to convert carriage
return characters in the log to line feeds. For example: `gunzip
-c ttyin | tr "\r" "\n"'
stdin The standard input when no terminal is present, or input
redirected from a pipe or file. This file is only present if the
log_input or log_stdin flags are set and the standard input is
not connected to a terminal.
ttyout Output from the pseudo-terminal (what the command writes to the
screen). Terminal-specific post-processing is performed before
the data is logged. This means that, for example, line feeds are
usually converted to line feed/carriage return pairs and tabs may
be expanded to spaces. This file is only present if the
log_output or log_ttyout flags are set and sudo was run from a
terminal.
stdout The standard output when no terminal is present, or output
redirected to a pipe or file. This file is only present if the
log_output or log_stdout flags are set and the standard output is
not connected to a terminal.
stderr The standard error when no terminal is present, or output
redirected to a pipe or file. This file is only present if the
log_output or log_stderr flags are set and the standard error is
not connected to a terminal.
All files other than log are compressed in gzip format unless the
compress_io flag has been disabled. Due to buffering, it is not normally
possible to display the I/O logs in real-time as the program is executing.
The I/O log data will not be complete until the program run by sudo has
exited or has been terminated by a signal. The iolog_flush flag can be
used to disable buffering, in which case I/O log data is written to disk as
soon as it is available. The output portion of an I/O log file can be
viewed with the sudoreplay(8) utility, which can also be used to list or
search the available logs.
User input may contain sensitive information such as passwords (even if
they are not echoed to the screen), which will be stored in the log file
unencrypted. In most cases, logging the command output via log_output or
LOG_OUTPUT is all that is required. When logging input, consider disabling
the log_passwords flag.
Since each session's I/O logs are stored in a separate directory,
traditional log rotation utilities cannot be used to limit the number of
I/O logs. The simplest way to limit the number of I/O is by setting the
maxseq option to the maximum number of logs you wish to store. Once the
I/O log sequence number reaches maxseq, it will be reset to zero and
sudoers will truncate and re-use any existing I/O logs.
FILES
/opt/local/etc/sudo.conf Sudo front-end configuration
/opt/local/etc/sudoers List of who can run what
/etc/group Local groups file
/etc/netgroup List of network groups
/var/log/sudo-io I/O log files
/opt/local/var/run/sudo/ts
Directory containing time stamps for the sudoers
security policy
/var/db/sudo/lectured Directory containing lecture status files for the
sudoers security policy
/etc/environment Initial environment for -i mode on AIX and Linux
systems
EXAMPLES
Below are example sudoers file entries. Admittedly, some of these are a
bit contrived. First, we allow a few environment variables to pass and
then define our aliases:
# Run X applications through sudo; HOME is used to find the
# .Xauthority file. Other programs use HOME to locate configuration
# files and this may lead to privilege escalation!
Defaults env_keep += "DISPLAY HOME"
# User alias specification
User_Alias FULLTIMERS = millert, mikef, dowdy
User_Alias PARTTIMERS = bostley, jwfox, crawl
User_Alias WEBADMIN = will, wendy, wim
# Runas alias specification
Runas_Alias OP = root, operator
Runas_Alias DB = oracle, sybase
Runas_Alias ADMINGRP = adm, oper
# Host alias specification
Host_Alias SPARC = bigtime, eclipse, moet, anchor :\
SGI = grolsch, dandelion, black :\
ALPHA = widget, thalamus, foobar :\
HPPA = boa, nag, python
Host_Alias CUNETS = 128.138.0.0/255.255.0.0
Host_Alias CSNETS = 128.138.243.0, 128.138.204.0/24, 128.138.242.0
Host_Alias SERVERS = primary, mail, www, ns
Host_Alias CDROM = orion, perseus, hercules
# Cmnd alias specification
Cmnd_Alias DUMPS = /usr/bin/mt, /usr/sbin/dump, /usr/sbin/rdump,\
/usr/sbin/restore, /usr/sbin/rrestore,\
sha224:0GomF8mNN3wlDt1HD9XldjJ3SNgpFdbjO1+NsQ== \
/home/operator/bin/start_backups
Cmnd_Alias KILL = /usr/bin/kill
Cmnd_Alias PRINTING = /usr/sbin/lpc, /usr/bin/lprm
Cmnd_Alias SHUTDOWN = /usr/sbin/shutdown
Cmnd_Alias HALT = /usr/sbin/halt
Cmnd_Alias REBOOT = /usr/sbin/reboot
Cmnd_Alias SHELLS = /usr/bin/sh, /usr/bin/csh, /usr/bin/ksh,\
/usr/local/bin/tcsh, /usr/bin/rsh,\
/usr/local/bin/zsh
Cmnd_Alias SU = /usr/bin/su
Cmnd_Alias PAGERS = /usr/bin/more, /usr/bin/pg, /usr/bin/less
Here we override some of the compiled in default values. We want sudo to
log via syslog(3) using the auth facility in all cases and for commands to
be run with the target user's home directory as the working directory. We
don't want to subject the full time staff to the sudo lecture and we want
to allow them to run commands in a chroot(2) "sandbox" via the -R option.
User millert need not provide a password and we don't want to reset the
LOGNAME or USER environment variables when running commands as root.
Additionally, on the machines in the SERVERS Host_Alias, we keep an
additional local log file and make sure we log the year in each log line
since the log entries will be kept around for several years. Lastly, we
disable shell escapes for the commands in the PAGERS Cmnd_Alias
(/usr/bin/more, /usr/bin/pg and /usr/bin/less). This will not effectively
constrain users with sudo ALL privileges.
# Override built-in defaults
Defaults syslog=auth,runcwd=~
Defaults>root !set_logname
Defaults:FULLTIMERS !lecture,runchroot=*
Defaults:millert !authenticate
Defaults@SERVERS log_year, logfile=/var/log/sudo.log
Defaults!PAGERS noexec
The User specification is the part that actually determines who may run
what.
root ALL = (ALL) ALL
%wheel ALL = (ALL) ALL
We let root and any user in group wheel run any command on any host as any
user.
FULLTIMERS ALL = NOPASSWD: ALL
Full time sysadmins (millert, mikef, and dowdy) may run any command on any
host without authenticating themselves.
PARTTIMERS ALL = ALL
Part time sysadmins bostley, jwfox, and crawl) may run any command on any
host but they must authenticate themselves first (since the entry lacks the
NOPASSWD tag).
jack CSNETS = ALL
The user jack may run any command on the machines in the CSNETS alias (the
networks 128.138.243.0, 128.138.204.0, and 128.138.242.0). Of those
networks, only 128.138.204.0 has an explicit netmask (in CIDR notation)
indicating it is a class C network. For the other networks in CSNETS, the
local machine's netmask will be used during matching.
lisa CUNETS = ALL
The user lisa may run any command on any host in the CUNETS alias (the
class B network 128.138.0.0).
operator ALL = DUMPS, KILL, SHUTDOWN, HALT, REBOOT, PRINTING,\
sudoedit /etc/printcap, /usr/oper/bin/
The operator user may run commands limited to simple maintenance. Here,
those are commands related to backups, killing processes, the printing
system, shutting down the system, and any commands in the directory
/usr/oper/bin/. One command in the DUMPS Cmnd_Alias includes a sha224
digest, /home/operator/bin/start_backups. This is because the directory
containing the script is writable by the operator user. If the script is
modified (resulting in a digest mismatch) it will no longer be possible to
run it via sudo.
joe ALL = /usr/bin/su operator
The user joe may only su(1) to operator.
pete HPPA = /usr/bin/passwd [A-Za-z]*, !/usr/bin/passwd *root*
%opers ALL = (: ADMINGRP) /usr/sbin/
Users in the opers group may run commands in /usr/sbin/ as themselves with
any group in the ADMINGRP Runas_Alias (the adm and oper groups).
The user pete is allowed to change anyone's password except for root on the
HPPA machines. Because command line arguments are matched as a single,
concatenated string, the `*' wildcard will match multiple words. This
example assumes that passwd(1) does not take multiple user names on the
command line. On systems with GNU getopt(3), options to passwd(1) may be
specified after the user argument. As a result, this rule will also allow:
passwd username --expire
which may not be desirable.
bob SPARC = (OP) ALL : SGI = (OP) ALL
The user bob may run anything on the SPARC and SGI machines as any user
listed in the OP Runas_Alias (root and operator.)
jim +biglab = ALL
The user jim may run any command on machines in the biglab netgroup. sudo
knows that "biglab" is a netgroup due to the `+' prefix.
+secretaries ALL = PRINTING, /usr/bin/adduser, /usr/bin/rmuser
Users in the secretaries netgroup need to help manage the printers as well
as add and remove users, so they are allowed to run those commands on all
machines.
fred ALL = (DB) NOPASSWD: ALL
The user fred can run commands as any user in the DB Runas_Alias (oracle or
sybase) without giving a password.
john ALPHA = /usr/bin/su [!-]*, !/usr/bin/su *root*
On the ALPHA machines, user john may su to anyone except root but he is not
allowed to specify any options to the su(1) command.
jen ALL, !SERVERS = ALL
The user jen may run any command on any machine except for those in the
SERVERS Host_Alias (primary, mail, www, and ns).
jill SERVERS = /usr/bin/, !SU, !SHELLS
For any machine in the SERVERS Host_Alias, jill may run any commands in the
directory /usr/bin/ except for those commands belonging to the SU and
SHELLS Cmnd_Aliases. While not specifically mentioned in the rule, the
commands in the PAGERS Cmnd_Alias all reside in /usr/bin and have the
noexec option set.
steve CSNETS = (operator) /usr/local/op_commands/
The user steve may run any command in the directory /usr/local/op_commands/
but only as user operator.
matt valkyrie = KILL
On his personal workstation, valkyrie, matt needs to be able to kill hung
processes.
WEBADMIN www = (www) ALL, (root) /usr/bin/su www
On the host www, any user in the WEBADMIN User_Alias (will, wendy, and
wim), may run any command as user www (which owns the web pages) or simply
su(1) to www.
ALL CDROM = NOPASSWD: /sbin/umount /CDROM,\
/sbin/mount -o nosuid\,nodev /dev/cd0a /CDROM
Any user may mount or unmount a CD-ROM on the machines in the CDROM
Host_Alias (orion, perseus, hercules) without entering a password. This is
a bit tedious for users to type, so it is a prime candidate for
encapsulating in a shell script.
SECURITY NOTES
Limitations of the `!' operator
It is generally not effective to "subtract" commands from ALL using the `!'
operator. A user can trivially circumvent this by copying the desired
command to a different name and then executing that. For example:
bill ALL = ALL, !SU, !SHELLS
Doesn't really prevent bill from running the commands listed in SU or
SHELLS since he can simply copy those commands to a different name, or use
a shell escape from an editor or other program. Therefore, these kind of
restrictions should be considered advisory at best (and reinforced by
policy).
In general, if a user has sudo ALL there is nothing to prevent them from
creating their own program that gives them a root shell (or making their
own copy of a shell) regardless of any `!' elements in the user
specification.
Security implications of fast_glob
If the fast_glob option is in use, it is not possible to reliably negate
commands where the path name includes globbing (aka wildcard) characters.
This is because the C library's fnmatch(3) function cannot resolve relative
paths. While this is typically only an inconvenience for rules that grant
privileges, it can result in a security issue for rules that subtract or
revoke privileges.
For example, given the following sudoers file entry:
john ALL = /usr/bin/passwd [a-zA-Z0-9]*, /usr/bin/chsh [a-zA-Z0-9]*,\
/usr/bin/chfn [a-zA-Z0-9]*, !/usr/bin/* root
User john can still run `/usr/bin/passwd root' if fast_glob is enabled by
changing to /usr/bin and running `./passwd root' instead.
Another potential issue is that when sudo executes the command, it must use
the command or path specified by the user instead of a path listed in the
sudoers file. This may lead to a time of check versus time of use race
condition.
Wildcards in command arguments
Command line arguments are matched as a single, concatenated string. This
mean a wildcard character such as `?' or `*' will match across word
boundaries, which may be unexpected. For example, while a sudoers entry
like:
%operator ALL = /bin/cat /var/log/messages*
will allow command like:
$ sudo cat /var/log/messages.1
It will also allow:
$ sudo cat /var/log/messages /etc/shadow
which is probably not what was intended. A safer alternative is to use a
regular expression for matching command line arguments. The above example
can be rewritten as a regular expression:
%operator ALL = /bin/cat ^/var/log/messages[^[:space:]]*$
The regular expression will only match a single file with a name that
begins with /var/log/messages and does not include any white space in the
name. It is often better to do command line processing outside of the
sudoers file in a scripting language for anything non-trivial.
Regular expressions in command names
Using a regular expression to match a command name has the same security
implications as using the fast_glob option:
o It is not possible to reliably negate commands when the path name is a
regular expression.
o When sudo executes the command, it must use the command or path
specified by the user instead of a path listed in the sudoers file.
This may lead to a time of check versus time of use race condition.
These issues do not apply to rules where only the command line options are
matched using a regular expression.
Preventing shell escapes
Once sudo executes a program, that program is free to do whatever it
pleases, including run other programs. This can be a security issue since
it is not uncommon for a program to allow shell escapes, which lets a user
bypass sudo's access control and logging. Common programs that permit
shell escapes include shells (obviously), editors, paginators, mail, and
terminal programs.
There are four basic approaches to this problem:
restrict Avoid giving users access to commands that allow the user to run
arbitrary commands. Many editors have a restricted mode where
shell escapes are disabled, though sudoedit is a better solution
to running editors via sudo. Due to the large number of
programs that offer shell escapes, restricting users to the set
of programs that do not is often unworkable.
intercept On most systems, sudo's intercept functionality can be used to
transparently intercept an attempt to run a new command, allow
or deny it based on sudoers rules, and log the result. For
example, this can be used to restrict the commands run from
within a privileged shell or editor.
There are two underlying mechanisms that may be used to
implement intercept mode: dso and trace. The intercept_type
setting can be used to select between them.
The first mechanism, dso, overrides the standard C library
functions that are used to execute a command. It does this by
setting an environment variable (usually LD_PRELOAD) to the path
of a dynamic shared object, or shared library, containing custom
versions of the execve(2), execl(3), execle(3), execlp(3),
execv(3), execvp(3), execvpe(3), and system(3) library functions
that connect back to sudo for a policy decision. Note, however,
that this applies only to dynamically-linked executables. It is
not possible to intercept commands for statically-linked
executables or executables that run under binary emulation this
way. Because most dynamic loaders ignore LD_PRELOAD (or the
equivalent) when running set-user-ID and set-group-ID programs,
sudoers will not permit such programs to be run in intercept
mode by default. The dso mechanism is incompatible with sudo's
SELinux RBAC support (but see below). SELinux disables
LD_PRELOAD by default and interferes with file descriptor
inheritance, which sudo relies on.
The second mechanism, trace, is available on Linux systems that
support seccomp(2) filtering. It uses ptrace(2) and seccomp(2)
to intercept the execve(2) system call instead of pre-loading a
dynamic shared object. Both static and dynamic executables are
supported and it is compatible with sudo's SELinux RBAC mode.
Functions utilizing the execveat(2) system call, such as
fexecve(3), are not currently intercepted.
The intercept feature is known to work on Solaris, *BSD, Linux,
macOS, HP-UX 11.x and AIX 5.3 and above. It should be supported
on most operating systems that support the LD_PRELOAD
environment variable or an equivalent. It is not possible to
intercept shell built-in commands or restrict the ability to
read or write sensitive files from within a shell.
To enable intercept mode on a per-command basis, use the
INTERCEPT tag as documented in the User Specification section
above. Here is that example again:
chuck research = INTERCEPT: ALL
This allows user chuck to run any command on the machine
"research" in intercept mode. Any commands run via shell
escapes will be validated and logged by sudo. If you are unsure
whether or not your system is capable of supporting intercept,
you can always just try it out and check whether or not external
commands run via a shell are logged when intercept is enabled.
There is an inherent race condition between when a command is
checked against sudoers rules and when it is actually executed.
If a user is allowed to run arbitrary commands, they may be able
to change the execve(2) arguments in the program after the
sudoers policy check has completed but before the new command is
executed. Starting with version 1.9.12, the trace method will
verify that the command and its arguments have not changed after
execve(2) has completed but before execution of the new program
has had a chance to run. This is not the case with the dso
method. See the description of the intercept_verify setting for
more information.
log There are two separate but related ways to log additional
commands. The first is to enable I/O logging using the
log_output flag. This will log the command's output but will
not create an event log entry when the additional command is
run. The second is to enable the log_subcmds flag in sudoers
which will create an event log entry every time a new command is
run. If I/O logging is also enabled, the log entry will include
a time offset into the I/O log to indicate when the command was
run. This offset can be passed to the sudoreplay(8) utility to
replay the I/O log at the exact moment when the command was run.
The log_subcmds flag uses the same mechanism as intercept (see
above) and has the same limitations.
noexec sudo's noexec functionality can be used to prevent a program run
by sudo from executing any other programs. On most systems, it
uses the same LD_PRELOAD mechanism as intercept (see above) and
thus the same caveats apply. The noexec functionality is
capable of blocking execution of commands run via the execve(2),
execl(3), execle(3), execlp(3), exect(3), execv(3), execveat(3),
execvP(3), execvp(3), execvpe(3), fexecve(3), popen(3),
posix_spawn(3), posix_spawnp(3), system(3), and wordexp(3)
functions. On Linux, a seccomp(2) filter is used to implement
noexec. On Solaris 10 and higher, noexec uses Solaris
privileges instead of the LD_PRELOAD environment variable.
To enable noexec for a command, use the NOEXEC tag as documented
in the User Specification section above. Here is that example
again:
aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi
This allows user aaron to run /usr/bin/more and /usr/bin/vi with
noexec enabled. This will prevent those two commands from
executing other commands (such as a shell). If you are unsure
whether or not your system is capable of supporting noexec you
can always just try it out and check whether shell escapes work
when noexec is enabled.
Restricting shell escapes is not a panacea. Programs running as root are
still capable of many potentially hazardous operations (such as changing or
overwriting files) that could lead to unintended privilege escalation. In
the specific case of an editor, a safer approach is to give the user
permission to run sudoedit (see below).
Secure editing
The sudoers plugin includes sudoedit support which allows users to securely
edit files with the editor of their choice. As sudoedit is a built-in
command, it must be specified in the sudoers file without a leading path.
However, it may take command line arguments just as a normal command does.
Wildcards used in sudoedit command line arguments are expected to be path
names, so a forward slash (`/') will not be matched by a wildcard.
Unlike other sudo commands, the editor is run with the permissions of the
invoking user and with the environment unmodified. More information may be
found in the description of the -e option in sudo(8).
For example, to allow user operator to edit the "message of the day" file
on any machine:
operator ALL = sudoedit /etc/motd
The operator user then runs sudoedit as follows:
$ sudoedit /etc/motd
The editor will run as the operator user, not root, on a temporary copy of
/etc/motd. After the file has been edited, /etc/motd will be updated with
the contents of the temporary copy.
Users should never be granted sudoedit permission to edit a file that
resides in a directory the user has write access to, either directly or via
a wildcard. If the user has write access to the directory it is possible
to replace the legitimate file with a link to another file, allowing the
editing of arbitrary files. To prevent this, starting with version 1.8.16,
symbolic links will not be followed in writable directories and sudoedit
will refuse to edit a file located in a writable directory unless the
sudoedit_checkdir option has been disabled or the invoking user is root.
Additionally, in version 1.8.15 and higher, sudoedit will refuse to open a
symbolic link unless either the sudoedit_follow option is enabled or the
sudoedit command is prefixed with the FOLLOW tag in the sudoers file.
Time stamp file checks
sudoers will check the ownership of its time stamp directory
(/opt/local/var/run/sudo/ts by default) and ignore the directory's contents
if it is not owned by root or if it is writable by a user other than root.
Older versions of sudo stored time stamp files in /tmp; this is no longer
recommended as it may be possible for a user to create the time stamp
themselves on systems that allow unprivileged users to change the ownership
of files they create.
While the time stamp directory should be cleared at reboot time, not all
systems contain a /run or /var/run directory. To avoid potential problems,
sudoers will ignore time stamp files that date from before the machine
booted on systems where the boot time is available.
Some systems with graphical desktop environments allow unprivileged users
to change the system clock. Since sudoers relies on the system clock for
time stamp validation, it may be possible on such systems for a user to run
sudo for longer than timestamp_timeout by setting the clock back. To
combat this, sudoers uses a monotonic clock (which never moves backwards)
for its time stamps if the system supports it.
sudoers will not honor time stamps set far in the future. Time stamps with
a date greater than current_time + 2 * TIMEOUT will be ignored and sudoers
will log and complain.
If the timestamp_type option is set to "tty", the time stamp record
includes the device number of the terminal the user authenticated with.
This provides per-terminal granularity but time stamp records may still
outlive the user's session.
Unless the timestamp_type option is set to "global", the time stamp record
also includes the session ID of the process that last authenticated. This
prevents processes in different terminal sessions from using the same time
stamp record. On systems where a process's start time can be queried, the
start time of the session leader is recorded in the time stamp record. If
no terminal is present or the timestamp_type option is set to "ppid", the
start time of the parent process is used instead. In most cases this will
prevent a time stamp record from being re-used without the user entering a
password when logging out and back in again.
DEBUGGING
Versions 1.8.4 and higher of the sudoers plugin support a flexible
debugging framework that can help track down what the plugin is doing
internally if there is a problem. This can be configured in the
sudo.conf(5) file.
The sudoers plugin uses the same debug flag format as the sudo front-end:
subsystem@priority.
The priorities used by sudoers, in order of decreasing severity, are: crit,
err, warn, notice, diag, info, trace, and debug. Each priority, when
specified, also includes all priorities higher than it. For example, a
priority of notice would include debug messages logged at notice and
higher.
The following subsystems are used by the sudoers plugin:
alias User_Alias, Runas_Alias, Host_Alias and Cmnd_Alias processing
all matches every subsystem
audit BSM and Linux audit code
auth user authentication
defaults sudoers file Defaults settings
env environment handling
ldap LDAP-based sudoers
logging logging support
match matching of users, groups, hosts, and netgroups in the sudoers
file
netif network interface handling
nss network service switch handling in sudoers
parser sudoers file parsing
perms permission setting
plugin The equivalent of main for the plugin.
pty pseudo-terminal related code
rbtree redblack tree internals
sssd SSSD-based sudoers
util utility functions
For example:
Debug sudoers.so /var/log/sudoers_debug match@info,nss@info
For more information, see the sudo.conf(5) manual.
SEE ALSO
ssh(1), su(1), fnmatch(3), glob(3), mktemp(3), strftime(3), sudo.conf(5),
sudo_plugin(5), sudoers.ldap(5), sudoers_timestamp(5), sudo(8), visudo(8)
AUTHORS
Many people have worked on sudo over the years; this version consists of
code written primarily by:
Todd C. Miller
See the CONTRIBUTORS.md file in the sudo distribution
(https://www.sudo.ws/about/contributors/) for an exhaustive list of people
who have contributed to sudo.
CAVEATS
The sudoers file should always be edited by the visudo utility which locks
the file and checks for syntax errors. If sudoers contains syntax errors,
sudo may refuse to run, which is a serious problem if sudo is your only
method of obtaining superuser privileges. Recent versions of sudoers will
attempt to recover after a syntax error by ignoring the rest of the line
after encountering an error. Older versions of sudo will not run if
sudoers contains a syntax error.
When using netgroups of machines (as opposed to users), if you store fully
qualified host name in the netgroup (as is usually the case), you either
need to have the machine's host name be fully qualified as returned by the
hostname command or use the fqdn option in sudoers.
BUGS
If you believe you have found a bug in sudo, you can submit a bug report at
https://bugzilla.sudo.ws/
SUPPORT
Limited free support is available via the sudo-users mailing list, see
https://www.sudo.ws/mailman/listinfo/sudo-users to subscribe or search the
archives.
DISCLAIMER
sudo is provided "AS IS" and any express or implied warranties, including,
but not limited to, the implied warranties of merchantability and fitness
for a particular purpose are disclaimed. See the LICENSE.md file
distributed with sudo or https://www.sudo.ws/about/license/ for complete
details.
Sudo 1.9.13 January 16, 2023 Sudo 1.9.13
sudo 1.9.13 - Generated Sat Feb 18 06:17:26 CST 2023