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.  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  format,  except  that  the two character sequence %m will be replaced by the error message string str-
       error(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 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 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 (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  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, sys-
       log() 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 3.25 of the Linux man-pages project.  A description of the project, and information about
       reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                                                      2008-11-12                                                  SYSLOG(3)