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 priori
ties 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 associ
ated 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 "open
log()" 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 pri ority 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 overrid
den.; 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 implic
itly by the contents of the Perl variable $! ($ERRNO).
@formatargs is a list of values that the format direc tives 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. Log
ging 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()". Usu
ally 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 func
tions.

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 (usu ally 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 printftype 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 net work 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. [Espe cially 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 mes sage 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 argu
ments. I will implement the string based calls if
there are enough people ($min_people > 10**40) com plaining about the lack of compatibility.

AUTHOR

Marcus Harnisch <marcus.harnisch@gmx.net>

docs.sk

comprehensive documentation repository

In section

See also