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sudoers_timestamp(5)        BSD File Formats Manual       sudoers_timestamp(5)


NAME

     sudoers_timestamp -- Sudoers Time Stamp Format


DESCRIPTION

     The sudoers plugin uses per-user time stamp files for credential caching.
     Once a user has been authenticated, they may 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 authenti-
     cated separately.  The timestamp_type option can be used to select the
     type of time stamp record sudoers will use.

     A multi-record time stamp file format was introduced in sudo 1.8.10 that
     uses a single file per user.  Previously, a separate file was used for
     each user and terminal combination unless tty-based time stamps were dis-
     abled.  The new format is extensible and records of multiple types and
     versions may coexist within the same file.

     All records, regardless of type or version, begin with a 16-bit version
     number and a 16-bit record size.

     Time stamp records have the following structure:

     /* Time stamp entry types */
     #define TS_GLOBAL               0x01    /* not restricted by tty or ppid */
     #define TS_TTY                  0x02    /* restricted by tty */
     #define TS_PPID                 0x03    /* restricted by ppid */
     #define TS_LOCKEXCL             0x04    /* special lock record */

     /* Time stamp flags */
     #define TS_DISABLED             0x01    /* entry disabled */
     #define TS_ANYUID               0x02    /* ignore uid, only valid in key */

     struct timestamp_entry {
         unsigned short version;     /* version number */
         unsigned short size;        /* entry size */
         unsigned short type;        /* TS_GLOBAL, TS_TTY, TS_PPID */
         unsigned short flags;       /* TS_DISABLED, TS_ANYUID */
         uid_t auth_uid;             /* uid to authenticate as */
         pid_t sid;                  /* session ID associated with tty/ppid */
         struct timespec start_time; /* session/ppid start time */
         struct timespec ts;         /* time stamp (CLOCK_MONOTONIC) */
         union {
             dev_t ttydev;           /* tty device number */
             pid_t ppid;             /* parent pid */
         } u;
     };

     The timestamp_entry struct fields are as follows:

     version
           The version number of the timestamp_entry struct.  New entries are
           created with a version number of 2.  Records with different version
           numbers may coexist in the same file but are not inter-operable.

     size  The size of the record in bytes.

     type  The record type, currently TS_GLOBAL, TS_TTY, or TS_PPID.

     flags
           Zero or more record flags which can be bit-wise ORed together.
           Supported flags are TS_DISABLED, for records disabled via sudo -k
           and TS_ANYUID, which is used only when matching records.

     auth_uid
           The user-ID that was used for authentication.  Depending on the
           value of the rootpw, runaspw and targetpw options, the user-ID may
           be that of the invoking user, the root user, the default runas user
           or the target user.

     sid   The ID of the user's terminal session, if present.  The session ID
           is only used when matching records of type TS_TTY.

     start_time
           The start time of the session leader for records of type TS_TTY or
           of the parent process for records of type TS_PPID.  The start_time
           is used to help prevent re-use of a time stamp record after a user
           has logged out.  Not all systems support a method to easily
           retrieve a process's start time.  The start_time field was added in
           sudoers version 1.8.22 for the second revision of the time-
           stamp_entry struct.

     ts    The actual time stamp.  A monotonic time source (which does not
           move backward) is used if the system supports it.  Where possible,
           sudoers uses a monotonic timer that increments even while the sys-
           tem is suspended.  The value of ts is updated each time a command
           is run via sudo.  If the difference between ts and the current time
           is less than the value of the timestamp_timeout option, no password
           is required.

     u.ttydev
           The device number of the terminal associated with the session for
           records of type TS_TTY.

     u.ppid
           The ID of the parent process for records of type TS_PPID.


LOCKING

     In sudoers versions 1.8.10 through 1.8.14, the entire time stamp file was
     locked for exclusive access when reading or writing to the file.  Start-
     ing in sudoers 1.8.15, individual records are locked in the time stamp
     file instead of the entire file and the lock is held for a longer period
     of time.  This scheme is described below.

     The first record in the time stamp file is of type TS_LOCKEXCL and is
     used as a lock record to prevent more than one sudo process from adding a
     new record at the same time.  Once the desired time stamp record has been
     located or created (and locked), the TS_LOCKEXCL record is unlocked.  The
     lock on the individual time stamp record, however, is held until authen-
     tication is complete.  This allows sudoers to avoid prompting for a pass-
     word multiple times when it is used more than once in a pipeline.

     Records of type TS_GLOBAL cannot be locked for a long period of time
     since doing so would interfere with other sudo processes.  Instead, a
     separate lock record is used to prevent multiple sudo processes using the
     same terminal (or parent process ID) from prompting for a password as the
     same time.


SEE ALSO

     sudoers(5), sudo(8)


HISTORY

     Originally, sudo used a single zero-length file per user and the file's
     modification time was used as the time stamp.  Later versions of sudo
     added restrictions on the ownership of the time stamp files and directory
     as well as checks on the validity of the time stamp itself.  Notable
     changes were introduced in the following sudo versions:

     1.4.0
           Support for tty-based time stamp file was added by appending the
           terminal name to the time stamp file name.

     1.6.2
           The time stamp file was replaced by a per-user directory which con-
           tained any tty-based time stamp files.

     1.6.3p2
           The target user name was added to the time stamp file name when the
           targetpw option was set.

     1.7.3
           Information about the terminal device was stored in tty-based time
           stamp files for validity checks.  This included the terminal device
           numbers, inode number and, on systems where it was not updated when
           the device was written to, the inode change time.  This helped pre-
           vent re-use of the time stamp file after logout.

     1.8.6p7
           The terminal session ID was added to tty-based time stamp files to
           prevent re-use of the time stamp by the same user in a different
           terminal session.  It also helped prevent re-use of the time stamp
           file on systems where the terminal device's inode change time was
           updated by writing.

     1.8.10
           A new, multi-record time stamp file format was introduced that uses
           a single file per user.  The terminal device's change time was not
           included since most systems now update the change time after a
           write is performed as required by POSIX.

     1.8.15
           Individual records are locked in the time stamp file instead of the
           entire file and the lock is held until authentication is complete.

     1.8.22
           The start time of the terminal session leader or parent process is
           now stored in non-global time stamp records.  This prevents re-use
           of the time stamp file after logout in most cases.

           Support was added for the kernel-based tty time stamps available in
           OpenBSD which do not use an on-disk time stamp file.


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 peo-
     ple who have contributed to sudo.


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, includ-
     ing, 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 1.9.10                    February 16, 2022                   Sudo 1.9.10

sudo 1.9.10 - Generated Wed Mar 9 05:48:33 CST 2022
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