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.
        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.

       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_ODELAY The converse of LOG_NDELAY; opening of the connection is delayed until syslog() is called.  (default, 
       LOG_NOWAIT   Don't wait for child processes that may have been created  while logging the message.  
       LOG_PERROR 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.

RFC 5424
 Numerical             Facility

              0             kernel messages         LOG_KERN
              1             user-level messages         
              2             mail system             LOG_MAIL
              3             system daemons
              4             security/authorization messages
              5             messages generated internally by syslogd
              6             line printer subsystem  LOG_LPR
              7             network news subsystem  LOG_NEWS USENET news subsystem 
              8             UUCP subsystem          LOG_UUCP
              9             clock daemon            LOG_CRON (cron and at)
             10             security/authorization messages
             11             FTP daemon              LOG_FTP
             12             NTP subsystem
             13             log audit
             14             log alert
             15             clock daemon (note 2)
             16             local use 0  (local0)
             17             local use 1  (local1)
             18             local use 2  (local2)
             19             local use 3  (local3)
             20             local use 4  (local4)
             21             local use 5  (local5)
             22             local use 6  (local6)
             23             local use 7  (local7) 

       LOG_AUTH     security/authorization  messages  (DEPRECATED  Use  LOG_AUTHPRIV instead) 
       LOG_AUTHPRIV security/authorization messages (private) 
       LOG_DAEMON   system daemons without separate facility value 
       LOG_LOCAL0 through LOG_LOCAL7 for local use 
       LOG_SYSLOG   internally by syslogd 
       LOG_USER (default) generic user-level messages 
     apple permits any value for the "Facility"  ( man syslogd)
        only processes running with UID 0 may log messages with a facility value of "", 
            or with a value that has "" as a prefix.  
        Messages logged by non UID 0 processes that use "" as a facility value or prefix 
        will be saved with the facility value "user".

       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 

Example <0>  KERN+EM; 
       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.
        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)