1SYSLOG(3) Linux Programmer's Manual SYSLOG(3)
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6 closelog, openlog, syslog, vsyslog - send messages to the system logger
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9 #include <syslog.h>
10 void openlog(const char *ident, int option, int facility);
12 void syslog(int priority, const char *format, ...);
13 void closelog(void);
14 #include <stdarg.h>
16 void vsyslog(int priority, const char *format, va_list ap);
18 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
20 vsyslog(): _BSD_SOURCE
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24 closelog() closes the descriptor being used to write to the system log‐
25 ger. The use of closelog() is optional.
26 openlog() opens a connection to the system logger for a program. The
28 string pointed to by ident is prepended to every message, and is typi‐
29 cally set to the program name. If ident is NULL, the program name is
30 used. (POSIX.1-2008 does not specify the behavior when ident is NULL.)
31 The option argument specifies flags which control the operation of
33 openlog() and subsequent calls to syslog(). The facility argument
34 establishes a default to be used if none is specified in subsequent
35 calls to syslog(). Values for option and facility are given below.
36 The use of openlog() is optional; it will automatically be called by
37 syslog() if necessary, in which case ident will default to NULL.
38 syslog() generates a log message, which will be distributed by sys‐
40 logd(8). The priority argument is formed by ORing the facility and the
41 level values (explained below). The remaining arguments are a format,
42 as in printf(3) and any arguments required by the format, except that
43 the two character sequence %m will be replaced by the error message
44 string strerror(errno). A trailing newline may be added if needed.
45 The function vsyslog() performs the same task as syslog() with the dif‐
47 ference that it takes a set of arguments which have been obtained using
48 the stdarg(3) variable argument list macros.
49 The subsections below list the parameters used to set the values of
51 option, facility, and priority.
52 option
54 The option argument to openlog() is an OR of any of these:
55 LOG_CONS Write directly to system console if there is an error
57 while sending to system logger.
58 LOG_NDELAY Open the connection immediately (normally, the connec‐
60 tion is opened when the first message is logged).
61 LOG_NOWAIT Don't wait for child processes that may have been cre‐
63 ated while logging the message. (The GNU C library does
64 not create a child process, so this option has no effect
65 on Linux.)
66 LOG_ODELAY The converse of LOG_NDELAY; opening of the connection is
68 delayed until syslog() is called. (This is the default,
69 and need not be specified.)
70 LOG_PERROR (Not in POSIX.1-2001 or POSIX.1-2008.) Print to stderr
72 as well.
73 LOG_PID Include PID with each message.
75 facility
77 The facility argument is used to specify what type of program is log‐
78 ging the message. This lets the configuration file specify that mes‐
79 sages from different facilities will be handled differently.
80 LOG_AUTH security/authorization messages
82 LOG_AUTHPRIV security/authorization messages (private)
84 LOG_CRON clock daemon (cron and at)
86 LOG_DAEMON system daemons without separate facility value
88 LOG_FTP ftp daemon
90 LOG_KERN kernel messages (these can't be generated from user pro‐
92 cesses)
93 LOG_LOCAL0 through LOG_LOCAL7
95 reserved for local use
96 LOG_LPR line printer subsystem
98 LOG_MAIL mail subsystem
100 LOG_NEWS USENET news subsystem
102 LOG_SYSLOG messages generated internally by syslogd(8)
104 LOG_USER (default)
106 generic user-level messages
107 LOG_UUCP UUCP subsystem
109 level
111 This determines the importance of the message. The levels are, in
112 order of decreasing importance:
113 LOG_EMERG system is unusable
115 LOG_ALERT action must be taken immediately
117 LOG_CRIT critical conditions
119 LOG_ERR error conditions
121 LOG_WARNING warning conditions
123 LOG_NOTICE normal, but significant, condition
125 LOG_INFO informational message
127 LOG_DEBUG debug-level message
129 The function setlogmask(3) can be used to restrict logging to specified
131 levels only.
132
134 The functions openlog(), closelog(), and syslog() (but not vsyslog())
135 are specified in SUSv2, POSIX.1-2001, and POSIX.1-2008. POSIX.1-2001
136 specifies only the LOG_USER and LOG_LOCAL* values for facility. How‐
137 ever, with the exception of LOG_AUTHPRIV and LOG_FTP, the other facil‐
138 ity values appear on most UNIX systems. The LOG_PERROR value for
139 option is not specified by POSIX.1-2001 or POSIX.1-2008, but is avail‐
140 able in most versions of UNIX.
141
143 The argument ident in the call of openlog() is probably stored as-is.
144 Thus, if the string it points to is changed, syslog() may start
145 prepending the changed string, and if the string it points to ceases to
146 exist, the results are undefined. Most portable is to use a string
147 constant.
148 Never pass a string with user-supplied data as a format, use the fol‐
150 lowing instead:
151 syslog(priority, "%s", string);
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155 logger(1), setlogmask(3), syslog.conf(5), syslogd(8)
156
158 This page is part of release 3.53 of the Linux man-pages project. A
159 description of the project, and information about reporting bugs, can
160 be found at http://www.kernel.org/doc/man-pages/.
161Linux 2012-08-17 SYSLOG(3)