SYSLOG(3)                   Linux Programmer's Manual                  SYSLOG(3)

       closelog, openlog, syslog, vsyslog - send messages to the system logger

       #include <syslog.h>

       void openlog(const char *ident, int option, int facility);
       void syslog(int priority, const char *format, ...);
       void closelog(void);

       #include <stdarg.h>

       void vsyslog(int priority, const char *format, va_list ap);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       vsyslog(): _BSD_SOURCE

       closelog() closes the descriptor being used to write to the system
       logger.  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
       typically 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
       syslogd(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
       difference 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.

       The option argument to openlog() is an OR of any of these:

       LOG_CONS       Write directly to system console if there is an error
                      while sending to system logger.

       LOG_NDELAY     Open the connection immediately (normally, the connection
                      is opened when the first message is logged).

       LOG_NOWAIT     Don't wait for child processes that may have been created
                      while logging the message.  (The GNU C library does not
                      create a child process, so this option has no effect on

       LOG_ODELAY     The converse of LOG_NDELAY; opening of the connection is
                      delayed until syslog() is called.  (This is the default,
                      and need not be specified.)

       LOG_PERROR     (Not in POSIX.1-2001 or POSIX.1-2008.)  Print to stderr as

       LOG_PID        Include PID with each message.

       The facility argument is used to specify what type of program is logging
       the message.  This lets the configuration file specify that messages from
       different facilities will be handled differently.

       LOG_AUTH       security/authorization messages

       LOG_AUTHPRIV   security/authorization messages (private)

       LOG_CRON       clock daemon (cron and at)

       LOG_DAEMON     system daemons without separate facility value

       LOG_FTP        ftp daemon

       LOG_KERN       kernel messages (these can't be generated from user

       LOG_LOCAL0 through LOG_LOCAL7
                      reserved for local use

       LOG_LPR        line printer subsystem

       LOG_MAIL       mail subsystem

       LOG_NEWS       USENET news subsystem

       LOG_SYSLOG     messages generated internally by syslogd(8)

       LOG_USER (default)
                      generic user-level messages

       LOG_UUCP       UUCP subsystem

       This determines the importance of the message.  The levels are, in order
       of decreasing importance:

       LOG_EMERG      system is unusable

       LOG_ALERT      action must be taken immediately

       LOG_CRIT       critical conditions

       LOG_ERR        error conditions

       LOG_WARNING    warning conditions

       LOG_NOTICE     normal, but significant, condition

       LOG_INFO       informational message

       LOG_DEBUG      debug-level message

       The function setlogmask(3) can be used to restrict logging to specified
       levels only.

       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 │
       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 LOG_USER and LOG_LOCAL* values for facility.  However,
       with the exception of LOG_AUTHPRIV and LOG_FTP, the other facility values
       appear on most UNIX systems.  The LOG_PERROR value for option is not
       specified by POSIX.1-2001 or POSIX.1-2008, but is available in most
       versions of UNIX.

       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

       Never pass a string with user-supplied data as a format, use the
       following instead:

           syslog(priority, "%s", string);

       logger(1), setlogmask(3), syslog.conf(5), syslogd(8)

       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

Linux                              2012-08-17                          SYSLOG(3)