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

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

     void
     vsyslog(int priority, const char *message, va_list 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 cap-
     tured 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 generating 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 users.

     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 possibly be handled spe-
		   cially.

     LOG_INFO	   Informational messages.

     LOG_DEBUG	   Messages that contain information normally of use only when debugging a pro-
		   gram.

     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 mes-
     sage.  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 (``/dev/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 identifying 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 individu-
		   als.

     LOG_CONSOLE   Messages written to /dev/console by the kernel console output 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 generated by any user pro-
		   cesses.

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

     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 LOG_LOCAL7.

     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 calculated by the macro LOG_MASK(pri); the mask for all priori-
     ties up to and including toppri is given by the macro LOG_UPTO(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(LOG_ALERT, "who: internal error 23");

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

	   setlogmask(LOG_UPTO(LOG_ERR));

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

	   syslog(LOG_INFO|LOG_LOCAL2, "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 interpola-
     tion by syslog().

     Always use the proper secure idiom:

	   syslog("%s", string);

BSD					December 30, 2004				      BSD
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