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



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, va_list ap);

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

       vsyslog(): _BSD_SOURCE

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.  The  option  argument  specifies  flags
       which  control  the operation of openlog() and subsequent calls to sys-
       log().  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:

       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 connec-
                      tion is opened when the first message is logged).

       LOG_NOWAIT     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.)

       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.)  Print to stderr as well.

       LOG_PID        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.

       LOG_AUTH       security/authorization    messages    (DEPRECATED    Use
                      LOG_AUTHPRIV instead)

       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 pro-
                      cesses)

       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

   level
       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.

CONFORMING TO
       The  functions  openlog(), closelog(), and syslog() (but not vsyslog())
       are specified in SUSv2 and POSIX.1-2001.  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, but is available 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 3.35 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://man7.org/linux/man-pages/.



Linux                             2008-11-12                         SYSLOG(3)



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