Man Linux: Main Page and Category List


       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);

       #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


       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 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.)  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    (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

       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.


       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.


       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 3.24 of the Linux  man-pages  project.   A
       description  of  the project, and information about reporting bugs, can
       be found at