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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);

       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  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 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 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 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.

ATTRIBUTES

       For   an   explanation   of   the  terms  used  in  this  section,  see
       attributes(7).

       ┌──────────────────────┬───────────────┬────────────────────┐
       │InterfaceAttributeValue              │
       ├──────────────────────┼───────────────┼────────────────────┤
       │openlog(), closelog() │ Thread safety │ MT-Safe            │
       ├──────────────────────┼───────────────┼────────────────────┤
       │syslog(), vsyslog()   │ Thread safety │ MT-Safe env locale │
       └──────────────────────┴───────────────┴────────────────────┘

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

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