closelog, openlog, syslog, vsyslog - send messages to the system logger


   #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)):

       Since glibc 2.19:
       Glibc 2.19 and earlier:


   closelog() closes the file 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

   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

   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.

   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.

   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

   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

   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.


   For   an   explanation   of   the  terms  used  in  this  section,  see

   │InterfaceAttributeValue              │
   │openlog(), closelog() │ Thread safety │ MT-Safe            │
   │syslog(), vsyslog()   │ Thread safety │ MT-Safe env locale │


   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.


   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

   Never pass a string with  user-supplied  data  as  a  format,  use  the
   following instead:

       syslog(priority, "%s", string);


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


   This  page  is  part of release 4.09 of the Linux man-pages project.  A
   description of the project, information about reporting bugs,  and  the
   latest     version     of     this    page,    can    be    found    at


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