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



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

SYNOPSIS
       #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

DESCRIPTION
       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 subse‐
       quent 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 for‐
       mat, 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.

   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 sys‐
                      tem 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 Linux.)

       LOG_ODELAY     The converse of LOG_NDELAY; opening of the connection is delayed until sys‐
                      log() 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 well.

       LOG_PID        Include PID with each message.

   facility
       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 processes)

       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,  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.

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 following instead:

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

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

COLOPHON
       This  page  is  part of release 3.74 of the Linux man-pages project.  A description of the
       project, information about reporting bugs, and the latest version of  this  page,  can  be
       found at http://www.kernel.org/doc/man-pages/.



Linux                                       2012-08-17                                  SYSLOG(3)