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



NAME
       closelog, openlog, syslog - 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);

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.  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  for-
       mat,  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  prior-
       ity.

   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 log-
              ger.

       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 mes-
              sage.  (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  logging  the  message.
       This  lets  the configuration file specify that messages 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 1003.1-2001.  POSIX 1003.1-2001 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 spec-
       ified by POSIX 1003.1-2001, but is available in most versions of Unix.

HISTORY
       A  syslog  function  call  appeared  in  BSD  4.2.  BSD 4.3 documents openlog(), syslog(),
       closelog(), and setlogmask().  4.3BSD-Reno also documents vsyslog().  Of course  early  v*
       functions used the  mechanism, which is not compatible with .

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)