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Unix::Syslog(3pm) - phpMan
Syslog(3pm) User Contributed Perl Documentation Syslog(3pm)
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 AT 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 AT gmx.net>
perl v5.20.0 2008-05-18 Syslog(3pm)
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