Sys::Syslog - Perl interface to the UNIX syslog(3) calls


Version 0.13


    use Sys::Syslog;                          # all except setlogsock(), or:
    use Sys::Syslog qw(:DEFAULT setlogsock);  # default set, plus setlogsock()
    use Sys::Syslog qw(:standard :macros);    # standard functions, plus macros
    setlogsock $sock_type;
    openlog $ident, $logopt, $facility;       # don't forget this
    syslog $priority, $format, @args;
    $oldmask = setlogmask $mask_priority;


Sys::Syslog is an interface to the UNIX syslog(3) program. Call syslog() with a string priority and a list of printf() args just like syslog(3).


Sys::Syslog exports the following Exporter tags:

By default, Sys::Syslog exports the symbols from the :standard tag.


openlog($ident, $logopt, $facility)

Opens the syslog. $ident is prepended to every message. $logopt contains zero or more of the words pid, ndelay, nowait. The cons option is ignored, since the failover mechanism will drop down to the console automatically if all other media fail. $facility specifies the part of the system to report about, for example LOG_USER or LOG_LOCAL0: see your syslog(3) documentation for the facilities available in your system. Facility can be given as a string or a numeric macro.

This function will croak if it can't connect to the syslog daemon.

Note that openlog() now takes three arguments, just like openlog(3).

You should use openlog() before calling syslog().



Open the syslog with options ndelay and pid, and with facility LOCAL0:

    openlog($name, "ndelay,pid", "local0");

Same thing, but this time using the macro corresponding to LOCAL0:

    openlog($name, "ndelay,pid", LOG_LOCAL0);
syslog($priority, $message)
syslog($priority, $format, @args)

If $priority permits, logs $message or sprintf($format, @args) with the addition that %m in $message or $format is replaced with "$!" (the latest error message).

$priority can specify a level, or a level and a facility. Levels and facilities can be given as strings or as macros.

If you didn't use openlog() before using syslog(), syslog() will try to guess the $ident by extracting the shortest prefix of $format that ends in a ":".


    syslog("info", $message);           # informational level
    syslog(LOG_INFO, $message);         # informational level
    syslog("info|local0", $message);        # information level, Local0 facility
    syslog(LOG_INFO|LOG_LOCAL0, $message);  # information level, Local0 facility

Sys::Syslog version v0.07 and older passed the $message as the formatting string to sprintf() even when no formatting arguments were provided. If the code calling syslog() might execute with older versions of this module, make sure to call the function as syslog($priority, "%s", $message) instead of syslog($priority, $message). This protects against hostile formatting sequences that might show up if $message contains tainted data.


Sets the log mask for the current process to $mask_priority and returns the old mask. If the mask argument is 0, the current log mask is not modified. See Levels for the list of available levels.


Only log errors:


Log critical messages, errors and warnings:

setlogsock($sock_type, $stream_location) (added in 5.004_02)

Sets the socket type to be used for the next call to openlog() or syslog() and returns true on success, undef on failure.

A value of "unix" will connect to the UNIX domain socket (in some systems a character special device) returned by the _PATH_LOG macro (if your system defines it), or /dev/log or /dev/conslog, whatever is writable. A value of 'stream' will connect to the stream indicated by the pathname provided as the optional second parameter. (For example Solaris and IRIX require "stream" instead of "unix".) A value of "inet" will connect to an INET socket (either tcp or udp, tried in that order) returned by getservbyname(). "tcp" and "udp" can also be given as values. The value "console" will send messages directly to the console, as for the "cons" option in the logopts in openlog().

A reference to an array can also be passed as the first parameter. When this calling method is used, the array should contain a list of sock_types which are attempted in order.

The default is to try tcp, udp, unix, stream, console.

Giving an invalid value for $sock_type will croak.


Closes the log file and return true on success.


    openlog($program, 'cons,pid', 'user');
    syslog('info', '%s', 'this is another test');
    syslog('mail|warning', 'this is a better test: %d', time);
    syslog('debug', 'this is the last test');
    openlog("$program $$", 'ndelay', 'user');
    syslog('notice', 'fooprogram: this is really done');
    $! = 55;
    syslog('info', 'problem was %m'); # %m == $! in syslog(3)
    # Log to UDP port on $remotehost instead of logging locally
    $Sys::Syslog::host = $remotehost;
    openlog($program, 'ndelay', 'user');
    syslog('info', 'something happened over here');





Invalid argument passed to setlogsock

(F) You gave setlogsock() an invalid value for $sock_type.

no connection to syslog available

(F) syslog() failed to connect to the specified socket.

stream passed to setlogsock, but %s is not writable

(W) You asked setlogsock() to use a stream socket, but the given path is not writable.

stream passed to setlogsock, but could not find any device

(W) You asked setlogsock() to use a stream socket, but didn't provide a path, and Sys::Syslog was unable to find an appropriate one.

tcp passed to setlogsock, but tcp service unavailable

(W) You asked setlogsock() to use a TCP socket, but the service is not available on the system.

syslog: expecting argument %s

(F) You forgot to give syslog() the indicated argument.

syslog: invalid level/facility: %s

(F) You specified an invalid level or facility, like LOG_KERN (which is reserved to the kernel).

syslog: too many levels given: %s

(F) You specified too many levels.

syslog: too many facilities given: %s

(F) You specified too many facilities.

syslog: level must be given

(F) You forgot to specify a level.

udp passed to setlogsock, but udp service unavailable

(W) You asked setlogsock() to use a UDP socket, but the service is not available on the system.

unix passed to setlogsock, but path not available

(W) You asked setlogsock() to use a UNIX socket, but Sys::Syslog was unable to find an appropriate an appropriate device.



Syslogging with Perl,


Tom Christiansen <> and Larry Wall <>.

UNIX domain sockets added by Sean Robinson <> with support from Tim Bunce <> and the perl5-porters mailing list.

Dependency on replaced with XS code by Tom Hughes <>.

Code for constant()s regenerated by Nicholas Clark <>.

Failover to different communication modes by Nick Williams <>.

Extracted from core distribution for publishing on the CPAN by Sébastien Aperghis-Tramoni <>.


Please report any bugs or feature requests to bug-sys-syslog at, or through the web interface at I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.


You can find documentation for this module with the perldoc command.

    perldoc Sys::Syslog

You can also look for information at:


This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.