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syslog(3)                BSD Library Functions Manual                syslog(3)


     closelog, openlog, setlogmask, syslog, vsyslog -- control system log


     Standard C Library (libc, -lc)


     #include <syslog.h>


     openlog(const char *ident, int logopt, int facility);

     setlogmask(int maskpri);

     syslog(int priority, const char *message, ...);

     #include <syslog.h>
     #include <stdarg.h>

     vsyslog(int priority, const char *message, va_list args);


     The syslog() function writes message to the system message logger.  The
     message is then written to the system console, log files, logged-in
     users, or forwarded to other machines as appropriate.  (See syslogd(8).)

     The message is identical to a printf(3) format string, except that `%m'
     is replaced by the current error message.  (As denoted by the global
     variable errno; see strerror(3).)  A trailing newline is added if none is

     Newlines and other non-printable characters embedded in the message
     string are printed in an alternate format.  This prevents someone from
     using non-printable characters to construct misleading log messages in an
     output file.  Newlines are printed as "\n", tabs are printed as "\t".
     Other control characters are printed using a caret ("^") representation,
     for example "^M" for carriage return.

     The vsyslog() function is an alternate form in which the arguments have
     already been captured using the variable-length argument facilities of

     The message is tagged with priority.  Priorities are encoded as a
     facility and a level.  The facility describes the part of the system gen-
     erating the message.  The level is selected from the following ordered
     (high to low) list:

     LOG_EMERG     A panic condition.  This is normally broadcast to all

     LOG_ALERT     A condition that should be corrected immediately, such as a
                   corrupted system database.

     LOG_CRIT      Critical conditions, e.g., hard device errors.

     LOG_ERR       Errors.

     LOG_WARNING   Warning messages.

     LOG_NOTICE    Conditions that are not error conditions, but should possi-
                   bly be handled specially.

     LOG_INFO      Informational messages.

     LOG_DEBUG     Messages that contain information normally of use only when
                   debugging a program.

     The openlog() function provides for more specialized processing of the
     messages sent by syslog() and vsyslog().  The parameter ident is a string
     that will be prepended to every message.  The logopt argument is a bit
     field specifying logging options, which is formed by OR'ing one or more
     of the following values:

     LOG_CONS      If syslog() cannot pass the message to syslogd(8) it will
                   attempt to write the message to the console

     LOG_NDELAY    Open the connection to syslogd(8) immediately.  Normally
                   the open is delayed until the first message is logged.
                   Useful for programs that need to manage the order in which
                   file descriptors are allocated.

     LOG_PERROR    Write the message to standard error output as well to the
                   system log.

     LOG_PID       Log the process id with each message: useful for identify-
                   ing instantiations of daemons.

     The facility parameter encodes a default facility to be assigned to all
     messages that do not have an explicit facility encoded:

     LOG_AUTH      The authorization system: login(1), su(1), getty(8), etc.

     LOG_AUTHPRIV  The same as LOG_AUTH, but logged to a file readable only by
                   selected individuals.

     LOG_CRON      The cron daemon: cron(8).

     LOG_DAEMON    System daemons, such as routed(8), that are not provided
                   for explicitly by other facilities.

     LOG_FTP       The file transfer protocol daemons: ftpd(8), tftpd(8).

     LOG_KERN      Messages generated by the kernel.  These cannot be gener-
                   ated by any user processes.

     LOG_LPR       The line printer spooling system: cups-lpd(8), cupsd(8),

     LOG_MAIL      The mail system.

     LOG_NEWS      The network news system.

     LOG_SECURITY  Security subsystems, such as ipfw(4).

     LOG_SYSLOG    Messages generated internally by syslogd(8).

     LOG_USER      Messages generated by random user processes.  This is the
                   default facility identifier if none is specified.

     LOG_UUCP      The uucp system.

     LOG_LOCAL0    Reserved for local use.  Similarly for LOG_LOCAL1 through

     The closelog() function can be used to close the log file.

     The setlogmask() function sets the log priority mask to maskpri and
     returns the previous mask.  Calls to syslog() with a priority not set in
     maskpri are rejected.  The mask for an individual priority pri is calcu-
     lated by the macro LOG_MASK(pri); the mask for all priorities up to and
     including toppri is given by the macro LOG_UPTO(toppri);.  The default
     allows all priorities to be logged.


     The routines closelog(), openlog(), syslog(), and vsyslog() return no

     The routine setlogmask() always returns the previous log mask level.


           syslog(LOG_ALERT, "who: internal error 23");

           openlog("ftpd", LOG_PID | LOG_NDELAY, LOG_FTP);


           syslog(LOG_INFO, "Connection from host %d", CallingHost);

           syslog(LOG_INFO|LOG_LOCAL2, "foobar error: %m");


     #include <syslog.h>
     #include <stdarg.h>

     These include files are necessary for all functions.


     asl(3), logger(1), compat(5), syslogd(8)


     These functions appeared in 4.2BSD.


     Never pass a string with user-supplied data as a format without using
     `%s'.  An attacker can put format specifiers in the string to mangle your
     stack, leading to a possible security hole.  This holds true even if the
     string was built using a function like snprintf(), as the resulting
     string may still contain user-supplied conversion specifiers for later
     interpolation by syslog().

     Always use the proper secure idiom:

           syslog(LOG_ERR, "%s", string);

BSD                              June 4, 1993                              BSD

Mac OS X 10.8 - Generated Fri Aug 31 15:46:07 CDT 2012
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