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. The option argument specifies flags
30 which control the operation of openlog() and subsequent calls to sys‐
31 log(). The facility argument establishes a default to be used if none
32 is specified in subsequent calls to syslog(). Values for option and
33 facility are given below. The use of openlog() is optional; it will
34 automatically be called by syslog() if necessary, in which case ident
35 will default to NULL.
36 syslog() generates a log message, which will be distributed by sys‐
38 logd(8). The priority argument is formed by ORing the facility and the
39 level values (explained below). The remaining arguments are a format,
40 as in printf(3) and any arguments required by the format, except that
41 the two character sequence %m will be replaced by the error message
42 string strerror(errno). A trailing newline may be added if needed.
43 The function vsyslog() performs the same task as syslog() with the dif‐
45 ference that it takes a set of arguments which have been obtained using
46 the stdarg(3) variable argument list macros.
47 The subsections below list the parameters used to set the values of
49 option, facility, and priority.
50 option
52 The option argument to openlog() is an OR of any of these:
53 LOG_CONS Write directly to system console if there is an error
55 while sending to system logger.
56 LOG_NDELAY Open the connection immediately (normally, the connec‐
58 tion is opened when the first message is logged).
59 LOG_NOWAIT Don't wait for child processes that may have been cre‐
61 ated while logging the message. (The GNU C library does
62 not create a child process, so this option has no effect
63 on Linux.)
64 LOG_ODELAY The converse of LOG_NDELAY; opening of the connection is
66 delayed until syslog() is called. (This is the default,
67 and need not be specified.)
68 LOG_PERROR (Not in POSIX.1-2001.) Print to stderr as well.
70 LOG_PID Include PID with each message.
72 facility
74 The facility argument is used to specify what type of program is log‐
75 ging the message. This lets the configuration file specify that mes‐
76 sages from different facilities will be handled differently.
77 LOG_AUTH security/authorization messages (DEPRECATED Use
79 LOG_AUTHPRIV instead)
80 LOG_AUTHPRIV security/authorization messages (private)
82 LOG_CRON clock daemon (cron and at)
84 LOG_DAEMON system daemons without separate facility value
86 LOG_FTP ftp daemon
88 LOG_KERN kernel messages (these can't be generated from user pro‐
90 cesses)
91 LOG_LOCAL0 through LOG_LOCAL7
93 reserved for local use
94 LOG_LPR line printer subsystem
96 LOG_MAIL mail subsystem
98 LOG_NEWS USENET news subsystem
100 LOG_SYSLOG messages generated internally by syslogd(8)
102 LOG_USER (default)
104 generic user-level messages
105 LOG_UUCP UUCP subsystem
107 level
109 This determines the importance of the message. The levels are, in
110 order of decreasing importance:
111 LOG_EMERG system is unusable
113 LOG_ALERT action must be taken immediately
115 LOG_CRIT critical conditions
117 LOG_ERR error conditions
119 LOG_WARNING warning conditions
121 LOG_NOTICE normal, but significant, condition
123 LOG_INFO informational message
125 LOG_DEBUG debug-level message
127 The function setlogmask(3) can be used to restrict logging to specified
129 levels only.
130
132 The functions openlog(), closelog(), and syslog() (but not vsyslog())
133 are specified in SUSv2 and POSIX.1-2001. POSIX.1-2001 specifies only
134 the LOG_USER and LOG_LOCAL* values for facility. However, with the
135 exception of LOG_AUTHPRIV and LOG_FTP, the other facility values appear
136 on most Unix systems. The LOG_PERROR value for option is not specified
137 by POSIX.1-2001, but is available in most versions of Unix.
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140 The argument ident in the call of openlog() is probably stored as-is.
141 Thus, if the string it points to is changed, syslog() may start
142 prepending the changed string, and if the string it points to ceases to
143 exist, the results are undefined. Most portable is to use a string
144 constant.
145 Never pass a string with user-supplied data as a format, use the fol‐
147 lowing instead:
148 syslog(priority, "%s", string);
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152 logger(1), setlogmask(3), syslog.conf(5), syslogd(8)
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155 This page is part of release 3.22 of the Linux man-pages project. A
156 description of the project, and information about reporting bugs, can
157 be found at http://www.kernel.org/doc/man-pages/.
158Linux 2008-11-12 SYSLOG(3)