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


       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);

closelog() closes the descriptor being used to write to the system logger.  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 is added when needed.

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.

       This  section  lists  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 SUSv3.) 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_LOCAL0 through LOG_LOCAL7 for local use 
       LOG_NEWS USENET news subsystem 
       LOG_SYSLOG internally by syslogd 
       LOG_USER (default) generic user-level messages 

       This  determines  the  importance  of  the message.  
       Order in decreasing importance:

0      LOG_EMERG system is unusable 
1      LOG_ALERT action must be taken immediately
2      LOG_CRIT critical 
3      LOG_ERR 
5      LOG_NOTICE normal, but significant, condition 
6      LOG_INFO 
7      LOG_DEBUG 

       The function setlogmask(3) can be used to restrict logging to specified levels only.

       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("%s", string);

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