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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 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 is added when 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.

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 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

       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 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.

HISTORY
       A syslog() function call appeared in 4.2BSD.   4.3BSD  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)
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