1Syslog(3) User Contributed Perl Documentation Syslog(3)
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6 Unix::Syslog - Perl interface to the UNIX syslog(3) calls
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9 use Unix::Syslog qw(:macros); # Syslog macros
10 use Unix::Syslog qw(:subs); # Syslog functions
11 openlog $ident, $option, $facility;
13 syslog $priority, $format, @formatargs;
14 closelog;
15 $oldmask = setlogmask $mask_priority;
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18 This module provides an interface to the system logger syslogd(8) via
19 Perl's XSUBs. The implementation attempts to resemble the native libc-
20 functions of your system, so that anyone being familiar with syslog.h
21 should be able to use this module right away.
22 In contrary to Sys::Syslog(3), this modules does not open a network
24 connection to send the messages. This can help you to avoid opening
25 security holes in your computer (see "FAQ").
26 The subs imported by the tag "macros" are simply wrappers around the
28 most important "#defines" in your system's C header file syslog.h. The
29 macros return integer values that are used to specify options,
30 facilities and priorities in a more or less portable way. They also
31 provide general information about your local syslog mechanism. Check
32 syslog(3) and your local syslog.h for information about the macros,
33 options and facilities available on your system.
34 The following functions are provided:
36 openlog $ident, $option, $facility
38 opens a connection to the system logger. $ident is an identifier
39 string that syslogd(8) prints into every message. It usually equals
40 the process name. $option is an integer value that is the result of
41 ORed options. $facility is an integer value that specifies the part
42 of the system the message should be associated with (e.g. kernel
43 message, mail subsystem).
44 syslog $priority, $format, @formatargs
46 Generates a log message and passes it to the system logger. If
47 "syslog()" is called without calling "openlog()" first, probably
48 system dependent default values will be used as arguments for an
49 implicit call to "openlog()".
50 $priority is an integer value that specifies the priority of the
52 message. Alternatively $priority can be the ORed value of a
53 priority and a facility. In that case a previously selected
54 facility will be overridden.
55 In the case that "syslog()" is called without calling "openlog()"
57 first and priority does not specify both a priority and a facility,
58 a default facility will be used. This behaviour is most likely
59 system dependent and the user should not rely on any particular
60 value in that case.
61 $format is a format string in the style of printf(3). Additionally
63 to the usual printf directives %m can be specified in the string.
64 It will be replaced implicitly by the contents of the Perl variable
65 $! ($ERRNO). @formatargs is a list of values that the format
66 directives will be replaced with subsequently.
67 closelog
69 closes the connection to the system logger.
70 setlogmask $mask_priority
72 sets the priority mask and returns the old mask. Logging is enabled
73 for the priorities indicated by the bits in the mask that are set
74 and is disabled where the bits are not set. Macros are provided to
75 specify valid and portable arguments to "setlogmask()". Usually the
76 default log mask allows all messages to be logged.
77 priorityname $priority
79 returns a string containing the name of $priority as string. If
80 this functionality has not been enabled at installation, the
81 function returns undef.
82 facilityname $facility
84 returns a string containing the name of $facility as string. If
85 this functionality has not been enabled at installation, the
86 function returns undef.
87 NOTE: The behaviour of this module is system dependent. It is highly
89 recommended to consult your system manual for available macros and the
90 behaviour of the provided functions.
91
93 The functions openlog(), syslog() and closelog() return the undefined
94 value. The function setlogmask returns the previous mask value.
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97 Open a channel to syslogd specifying an identifier (usually the process
98 name) some options and the facility:
99 "openlog "test.pl", LOG_PID | LOG_PERROR, LOG_LOCAL7;"
100 Generate log message of specified priority using a printf-type
102 formatted string:
103 "syslog LOG_INFO, "This is message number %d", 42;"
104 Set log priority mask to block all messages but those of priority
106 "LOG_DEBUG":
107 "$oldmask = setlogmask(LOG_MASK(LOG_DEBUG))"
108 Set log priority mask to block all messages with a higher priority than
110 "LOG_ERR":
111 "$oldmask = setlogmask(LOG_UPTO(LOG_ERR))"
112 Close channel to syslogd:
114 "closelog;"
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117 1. What is the benefit of using this module instead of Sys::Syslog?
118 Sys::Syslog always opens a network connection to the syslog
120 service. At least on Linux systems this may lead to some trouble,
121 because
122 • Linux syslogd (from package sysklogd) does not listen to the
124 network by default. Most people working on stand-alone machines
125 (including me) didn't see any reason why to enable this option.
126 Others didn't enable it for security reasons.
127 OS-independent, some sysadmins may run a firewall on their
129 network that blocks connections to port 514/udp.
130 • By default Linux syslogd doesn't forward messages which have
132 already already received from the network to other log hosts.
133 There are reasons not to enable this option unless it is really
134 necessary. Looping messages resulting from a misconfiguration
135 may break down your (log-)system.
136 Peter Stamfest <peter.stamfest@eunet.at> pointed out some other
138 advantages of Unix::Syslog, I didn't came across my self.
139 • LOG_PERROR works.
141 • works with perl -Tw without warnings and problems due to
143 tainted data as it is the case for Sys::Syslog in some special
144 applications. [Especially when running a script as root]
145 2. Well, is there any reason to use Sys::Syslog any longer?
147 Yes! In contrary to Unix::Syslog, Sys::Syslog works even if you
149 don't have a syslog daemon running on your system as long as you
150 are connected to a log host via a network and have access to the
151 syslog.h header file of your log host to generate the initial files
152 for Sys::Syslog (see Sys::Syslog(3) for details). Unix::Syslog only
153 logs to your local syslog daemon which in turn may be configured to
154 distribute the message over the network.
155 3. Are calls to the functions provided by Unix::Syslog compatible to
157 those of Sys::Syslog?
158 Currently not. Sys::Syslog requires strings to specify many of the
160 arguments to the functions, while Unix::Syslog uses numeric
161 constants accessed via macros as defined in syslog.h. Although the
162 strings used by Sys::Syslog are also defined in syslog.h, it seems
163 that most people got used to the numeric arguments. I will
164 implement the string based calls if there are enough people
165 ($min_people > 10**40) complaining about the lack of compatibility.
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168 syslog(3), Sys::Syslog(3), syslogd(8), perl(1)
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171 Marcus Harnisch <marcus.harnisch@gmx.net>
172perl v5.36.0 2022-07-22 Syslog(3)