Syslog(3) User Contributed Perl Documentation Syslog(3)
NAME
Unix::Syslog - Perl interface to the UNIX syslog(3) calls
SYNOPSIS
use Unix::Syslog qw(:macros); # Syslog macros
use Unix::Syslog qw(:subs); # Syslog functions
openlog $ident, $option, $facility;
syslog $priority, $format, @formatargs;
closelog;
$oldmask = setlogmask $mask_priority;
DESCRIPTION
This module provides an interface to the system logger syslogd(8) via Perl's XSUBs. The
implementation attempts to resemble the native libc-functions of your system, so that anyone being
familiar with syslog.h should be able to use this module right away.
In contrary to Sys::Syslog(3), this modules does not open a network connection to send the messages.
This can help you to avoid opening security holes in your computer (see "FAQ").
The subs imported by the tag "macros" are simply wrappers around the most important "#defines" in
your system's C header file syslog.h. The macros return integer values that are used to specify
options, facilities and priorities in a more or less portable way. They also provide general
information about your local syslog mechanism. Check syslog(3) and your local syslog.h for
information about the macros, options and facilities available on your system.
The following functions are provided:
openlog $ident, $option, $facility
opens a connection to the system logger. $ident is an identifier string that syslogd(8) prints
into every message. It usually equals the process name. $option is an integer value that is the
result of ORed options. $facility is an integer value that specifies the part of the system the
message should be associated with (e.g. kernel message, mail subsystem).
syslog $priority, $format, @formatargs
Generates a log message and passes it to the system logger. If "syslog()" is called without
calling "openlog()" first, probably system dependent default values will be used as arguments for
an implicit call to "openlog()".
$priority is an integer value that specifies the priority of the message. Alternatively $priority
can be the ORed value of a priority and a facility. In that case a previously selected facility
will be overridden.
In the case that "syslog()" is called without calling "openlog()" first and priority does not
specify both a priority and a facility, a default facility will be used. This behaviour is most
likely system dependent and the user should not rely on any particular value in that case.
$format is a format string in the style of printf(3). Additionally to the usual printf directives
%m can be specified in the string. It will be replaced implicitly by the contents of the Perl
variable $! ($ERRNO). @formatargs is a list of values that the format directives will be replaced
with subsequently.
closelog
closes the connection to the system logger.
setlogmask $mask_priority
sets the priority mask and returns the old mask. Logging is enabled for the priorities indicated
by the bits in the mask that are set and is disabled where the bits are not set. Macros are
provided to specify valid and portable arguments to "setlogmask()". Usually the default log mask
allows all messages to be logged.
priorityname $priority
returns a string containing the name of $priority as string. If this functionality has not been
enabled at installation, the function returns undef.
facilityname $facility
returns a string containing the name of $facility as string. If this functionality has not been
enabled at installation, the function returns undef.
NOTE: The behaviour of this module is system dependent. It is highly recommended to consult your
system manual for available macros and the behaviour of the provided functions.
RETURN VALUES
The functions openlog(), syslog() and closelog() return the undefined value. The function setlogmask
returns the previous mask value.
EXAMPLES
Open a channel to syslogd specifying an identifier (usually the process name) some options and the
facility:
"openlog "test.pl", LOG_PID | LOG_PERROR, LOG_LOCAL7;"
Generate log message of specified priority using a printf-type formatted string:
"syslog LOG_INFO, "This is message number %d", 42;"
Set log priority mask to block all messages but those of priority "LOG_DEBUG":
"$oldmask = setlogmask(LOG_MASK(LOG_DEBUG))"
Set log priority mask to block all messages with a higher priority than "LOG_ERR":
"$oldmask = setlogmask(LOG_UPTO(LOG_ERR))"
Close channel to syslogd:
"closelog;"
FAQ
1. What is the benefit of using this module instead of Sys::Syslog?
Sys::Syslog always opens a network connection to the syslog service. At least on Linux systems
this may lead to some trouble, because
Linux syslogd (from package sysklogd) does not listen to the network by default. Most people
working on stand-alone machines (including me) didn't see any reason why to enable this
option. Others didn't enable it for security reasons.
OS-independent, some sysadmins may run a firewall on their network that blocks connections to
port 514/udp.
By default Linux syslogd doesn't forward messages which have already already received from
the network to other log hosts. There are reasons not to enable this option unless it is
really necessary. Looping messages resulting from a misconfiguration may break down your
(log-)system.
Peter Stamfest <peter.stamfest@eunet.at> pointed out some other advantages of Unix::Syslog, I
didn't came across my self.
LOG_PERROR works.
works with perl -Tw without warnings and problems due to tainted data as it is the case for
Sys::Syslog in some special applications. [Especially when running a script as root]
2. Well, is there any reason to use Sys::Syslog any longer?
Yes! In contrary to Unix::Syslog, Sys::Syslog works even if you don't have a syslog daemon
running on your system as long as you are connected to a log host via a network and have access
to the syslog.h header file of your log host to generate the initial files for Sys::Syslog (see
Sys::Syslog(3) for details). Unix::Syslog only logs to your local syslog daemon which in turn may
be configured to distribute the message over the network.
3. Are calls to the functions provided by Unix::Syslog compatible to those of Sys::Syslog?
Currently not. Sys::Syslog requires strings to specify many of the arguments to the functions,
while Unix::Syslog uses numeric constants accessed via macros as defined in syslog.h. Although
the strings used by Sys::Syslog are also defined in syslog.h, it seems that most people got used
to the numeric arguments. I will implement the string based calls if there are enough people
($min_people > 10**40) complaining about the lack of compatibility.
SEE ALSO
syslog(3), Sys::Syslog(3), syslogd(8), perl(1)
AUTHOR
Marcus Harnisch <marcus.harnisch@gmx.net>
perl v5.8.8 2002-08-14 Syslog(3)
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