syslog

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



NAME
       closelog, openlog, syslog - 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);

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 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 is added
       when 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.

PARAMETERS
       This section lists 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  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 syslog() is called.	 (This is  the	default,  and
	      need not be specified.)

       LOG_PERROR
	      (Not in SUSv3.) 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

       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

       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 speci-
       fied levels only.

CONFORMING TO
       The functions openlog(), closelog(), and syslog() (but not  vsyslog())
       are specified in SUSv2 and POSIX 1003.1-2001.  POSIX 1003.1-2001 spec-
       ifies 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 1003.1-2001, but is available in most ver-
       sions of Unix.

HISTORY
       A syslog function call appeared in BSD 4.2.  BSD 4.3  documents	open-
       log(), syslog(), closelog(), and setlogmask().  4.3BSD-Reno also docu-
       ments vsyslog().	 Of course early v* functions  used  the  <varargs.h>
       mechanism, which is not compatible with <stdarg.h>.

NOTES
       The parameter 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
	      syslog(priority, "%s", string);
       instead.

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



Linux				  2002-01-03			    SYSLOG(3)