NAME
closelog, openlog, syslog, vsyslog - send messages to the system logger SYNOPSIS
#include
void openlog(const char *ident, int option, int facility); void syslog(int priority, const char *format, ...); void closelog(void); #include
void vsyslog(int priority, const char *format, valist ap); Feature Test Macro Requirements for glibc (see featuretestmacros(7)): vsyslog(): BSDSOURCE DESCRIPTION closelog() closes the descriptor being used to write to the system log‐ ger. The use of closelog() is optional. openlog() opens a connection to the system logger for a program. The string pointed to by ident is prepended to every message, and is typi‐ cally set to the program name. If ident is NULL, the program name is used. (POSIX.1-2008 does not specify the behavior when ident is NULL.) The option argument specifies flags which control the operation of openlog() and subsequent calls to syslog(). The facility argument establishes a default to be used if none is specified in subsequent calls to syslog(). Values for option and facility are given below. The use of openlog() is optional; it will automatically be called by syslog() if necessary, in which case ident will default to NULL. syslog() generates a log message, which will be distributed by sys‐ logd(8). The priority argument is formed by ORing the facility and the level values (explained below). The remaining arguments are a format, as in printf(3) and any arguments required by the format, except that
the two character sequence %m will be replaced by the error message string strerror(errno). A trailing newline may be added if needed. The function vsyslog() performs the same task as syslog() with the dif‐ ference that it takes a set of arguments which have been obtained using the stdarg(3) variable argument list macros. The subsections below list the parameters used to set the values of option, facility, and priority. option The option argument to openlog() is an OR of any of these: LOGCONS Write directly to system console if there is an error while sending to system logger. LOGNDELAY Open the connection immediately (normally, the connec‐ tion is opened when the first message is logged). LOGNOWAIT Don't wait for child processes that may have been cre‐ ated while logging the message. (The GNU C library does not create a child process, so this option has no effect on Linux.) LOGODELAY The converse of LOGNDELAY; opening of the connection is delayed until syslog() is called. (This is the default, and need not be specified.)
LOGPERROR (Not in POSIX.1-2001 or POSIX.1-2008.) Print to stderr as well. LOGPID Include PID with each message. facility The facility argument is used to specify what type of program is log‐ ging the message. This lets the configuration file specify that mes‐ sages from different facilities will be handled differently. LOGAUTH security/authorization messages LOGAUTHPRIV security/authorization messages (private) LOGCRON clock daemon (cron and at) LOGDAEMON system daemons without separate facility value LOGFTP ftp daemon LOGKERN kernel messages (these can't be generated from user pro‐ cesses) LOGLOCAL0 through LOGLOCAL7 reserved for local use LOGLPR line printer subsystem LOGMAIL mail subsystem LOGNEWS USENET news subsystem LOGSYSLOG messages generated internally by syslogd(8) LOGUSER (default)
generic user-level messages LOGUUCP UUCP subsystem level This determines the importance of the message. The levels are, in order of decreasing importance: LOGEMERG system is unusable LOGALERT action must be taken immediately LOGCRIT critical conditions LOGERR error conditions LOGWARNING warning conditions LOGNOTICE normal, but significant, condition LOGINFO informational message
LOGDEBUG debug-level message The function setlogmask(3) can be used to restrict logging to specified levels only. ATTRIBUTES For an explanation of the terms used in this section, see attributes(7). ┌──────────────────────┬───────────────┬────────────────────┐ │Interface │ Attribute │ Value │ ├──────────────────────┼───────────────┼────────────────────┤
│openlog(), closelog() │ Thread safety │ MT-Safe │ ├──────────────────────┼───────────────┼────────────────────┤
│syslog(), vsyslog() │ Thread safety │ MT-Safe env locale │ └──────────────────────┴───────────────┴────────────────────┘ CONFORMING TO The functions openlog(), closelog(), and syslog() (but not vsyslog())
are specified in SUSv2, POSIX.1-2001, and POSIX.1-2008. POSIX.1-2001 specifies only the LOGUSER and LOGLOCAL* values for facility. How‐ ever, with the exception of LOGAUTHPRIV and LOGFTP, the other facil‐ ity values appear on most UNIX systems. The LOGPERROR value for
option is not specified by POSIX.1-2001 or POSIX.1-2008, but is avail‐ able in most versions of UNIX. NOTES
The argument ident in the call of openlog() is probably stored as-is. Thus, if the string it points to is changed, syslog() may start prepending the changed string, and if the string it points to ceases to exist, the results are undefined. Most portable is to use a string constant.
Never pass a string with user-supplied data as a format, use the fol‐ lowing instead:
syslog(priority, "%s", string); SEE ALSO logger(1), setlogmask(3), syslog.conf(5), syslogd(8) COLOPHON
This page is part of release 3.53 of the Linux man-pages project. A description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
Linux 2012-08-17 SYSLOG(3)