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

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

     Standard C Library (libc, -lc)

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

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

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

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


     setlogmask(int maskpri);

     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

     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 ident argument 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 argument 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_CONSOLE   Messages written to /dev/console by the kernel console out‐
		   put driver.

     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: lpr(1), lpc(8), lpd(8),

     LOG_MAIL	   The mail system.

     LOG_NEWS	   The network news system.

     LOG_NTP	   The network time protocol 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");

     logger(1), 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("%s", string);

BSD			       December 30, 2004			   BSD

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