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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>
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