SYSLOG(3)                BSD Library Functions Manual                SYSLOG(3)

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

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     ##include <>
     ##include <>

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

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

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

     void
     closelog(void);

     int
     setlogmask(int maskpri);

DESCRIPTION
     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
     present.

     The vsyslog() function is an alternate form in which the arguments have
     already been captured using the variable-length argument facilities of
     stdarg(3).

     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:

     LOGEMERG     A panic condition.  This is normally broadcast to all
                   users.

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

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

     LOGER       Errors.

     LOGWARNING   Warning messages.

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

     LOGINFO      Informational messages.

     LOGDEBUG     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:

     LOGCONS      If syslog() cannot pass the message to syslogd(8) it will
                   attempt to write the message to the console
                   (``/dev/console'').

     LOGNDELAY    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.

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

     LOGPID       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:

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

     LOGAUTHPRIV  The same as LOGAUTH, but logged to a file readable only by
                   selected individuals.

     LOGCONSOLE   Messages written to /dev/console by the kernel console out-
                   put driver.

     LOGCRON      The cron daemon: cron(8).

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

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

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

     LOGLPR       The line printer spooling system: lpr(1), lpc(8), lpd(8),
                   etc.

     LOGMAIL      The mail system.

     LOGNEWS      The network news system.

     LOGSECURITY  Security subsystems, such as ipfw(4).

     LOGSYSLOG    Messages generated internally by syslogd(8).

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

     LOGUCP      The uucp system.

     LOGLOCAL0    Reserved for local use.  Similarly for LOGLOCAL1 through
                   LOGLOCAL7.

     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 LOGMASK(pri); the mask for all priorities up to and
     including toppri is given by the macro LOGUPTO(toppri);.  The default
     allows all priorities to be logged.

RETURN VALUES
     The routines closelog(), openlog(), syslog() and vsyslog() return no
     value.

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

EXAMPLES
           syslog(LOGALERT, "who: internal error 23");

           openlog("ftpd", LOGPID  LOGNDELAY, LOGFTP);

           setlogmask(LOGUPTO(LOGER));

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

           syslog(LOGINFOLOGLOCAL2, "foobar error: %m");

SEE ALSO
     logger(1), syslogd(8)

HISTORY
     These functions appeared in 4.2BSD.

BUGS
     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(LOGER, %s, string);

BSD                              June 4, 1993                              BSD