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Linux 2.6 - man page for openlog (linux section 3posix)

CLOSELOG(P)			    POSIX Programmer's Manual			      CLOSELOG(P)

NAME
       closelog, openlog, setlogmask, syslog - control system log

SYNOPSIS
       #include <syslog.h>

       void closelog(void);
       void openlog(const char *ident, int logopt, int facility);
       int setlogmask(int maskpri);
       void syslog(int priority, const char *message, ... /* arguments */);

DESCRIPTION
       The  syslog() function shall send a message to an implementation-defined logging facility,
       which may log it in an implementation-defined system log, write it to the system  console,
       forward	it to a list of users, or forward it to the logging facility on another host over
       the network. The logged message shall include a message header and  a  message  body.  The
       message header contains at least a timestamp and a tag string.

       The  message body is generated from the message and following arguments in the same manner
       as if these were arguments to printf(), except that the additional  conversion  specifica-
       tion  %m shall be recognized; it shall convert no arguments, shall cause the output of the
       error message string associated with the value of errno on entry to syslog(), and  may  be
       mixed with argument specifications of the "%n$" form.  If a complete conversion specifica-
       tion with the m conversion specifier character is not just %m , the behavior is undefined.
       A trailing <newline> may be added if needed.

       Values  of  the priority argument are formed by OR'ing together a severity-level value and
       an optional facility value. If no facility value is specified, the current default  facil-
       ity value is used.

       Possible values of severity level include:

       LOG_EMERG
	      A panic condition.

       LOG_ALERT
	      A  condition that should be corrected immediately, such as a corrupted system data-
	      base.

       LOG_CRIT
	      Critical conditions, such as hard device errors.

       LOG_ERR
	      Errors.

       LOG_WARNING

	      Warning messages.

       LOG_NOTICE
	      Conditions that are not error conditions, but that may require special handling.

       LOG_INFO
	      Informational messages.

       LOG_DEBUG
	      Messages that contain information normally of use only when debugging a program.

       The facility indicates the application or system component generating the message.  Possi-
       ble facility values include:

       LOG_USER
	      Messages	generated by arbitrary processes. This is the default facility identifier
	      if none is specified.

       LOG_LOCAL0
	      Reserved for local use.

       LOG_LOCAL1
	      Reserved for local use.

       LOG_LOCAL2
	      Reserved for local use.

       LOG_LOCAL3
	      Reserved for local use.

       LOG_LOCAL4
	      Reserved for local use.

       LOG_LOCAL5
	      Reserved for local use.

       LOG_LOCAL6
	      Reserved for local use.

       LOG_LOCAL7
	      Reserved for local use.

       The openlog() function shall set process attributes that affect subsequent calls  to  sys-
       log(). The ident argument is a string that is prepended to every message. The logopt argu-
       ment indicates logging options. Values for logopt are constructed by  a	bitwise-inclusive
       OR of zero or more of the following:

       LOG_PID
	      Log  the process ID with each message. This is useful for identifying specific pro-
	      cesses.

       LOG_CONS
	      Write messages to the system console if they cannot be sent to the  logging  facil-
	      ity. The syslog() function ensures that the process does not acquire the console as
	      a controlling terminal in the process of writing the message.

       LOG_NDELAY
	      Open the connection to the logging  facility  immediately.  Normally  the  open  is
	      delayed until the first message is logged. This is useful for programs that need to
	      manage the order in which file descriptors are allocated.

       LOG_ODELAY
	      Delay open until syslog() is called.

       LOG_NOWAIT
	      Do not wait for child processes that may have been created  during  the  course  of
	      logging  the message. This option should be used by processes that enable notifica-
	      tion of child termination using SIGCHLD, since syslog() may otherwise block waiting
	      for a child whose exit status has already been collected.

       The  facility  argument	encodes a default facility to be assigned to all messages that do
       not have an explicit facility already encoded. The initial default facility is LOG_USER.

       The openlog() and syslog() functions may allocate a file descriptor. It is  not	necessary
       to call openlog() prior to calling syslog().

       The  closelog() function shall close any open file descriptors allocated by previous calls
       to openlog() or syslog().

       The setlogmask() function shall set the log priority  mask  for	the  current  process  to
       maskpri	and  return the previous mask. If the maskpri argument is 0, the current log mask
       is not modified. Calls by the current process to syslog()  with	a  priority  not  set  in
       maskpri	shall  be  rejected.   The default log mask allows all priorities to be logged. A
       call to openlog() is not required prior to calling setlogmask().

       Symbolic constants for use as values of the logopt, facility, priority, and maskpri  argu-
       ments are defined in the <syslog.h> header.

RETURN VALUE
       The  setlogmask()  function  shall  return the previous log priority mask. The closelog(),
       openlog(), and syslog() functions shall not return a value.

ERRORS
       No errors are defined.

       The following sections are informative.

EXAMPLES
   Using openlog()
       The following example causes subsequent calls to syslog() to log the process ID with  each
       message, and to write messages to the system console if they cannot be sent to the logging
       facility.

	      #include <syslog.h>

	      char *ident = "Process demo";
	      int logopt = LOG_PID | LOG_CONS;
	      int facility = LOG_USER;
	      ...
	      openlog(ident, logopt, facility);

   Using setlogmask()
       The following example causes subsequent calls to syslog() to accept error messages, and to
       reject all other messages.

	      #include <syslog.h>

	      int result;
	      int mask = LOG_MASK (LOG_ERR);
	      ...
	      result = setlogmask(mask);

   Using syslog
       The  following example sends the message "This is a message" to the default logging facil-
       ity, marking the message as an error message generated by random processes.

	      #include <syslog.h>

	      char *message = "This is a message";
	      int priority = LOG_ERR | LOG_USER;
	      ...
	      syslog(priority, message);

APPLICATION USAGE
       None.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       printf() , the Base Definitions volume of IEEE Std 1003.1-2001, <syslog.h>

COPYRIGHT
       Portions of this text are reprinted and	reproduced  in	electronic  form  from	IEEE  Std
       1003.1,	2003  Edition,	Standard  for Information Technology -- Portable Operating System
       Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003  by
       the  Institute  of  Electrical  and  Electronics Engineers, Inc and The Open Group. In the
       event of any discrepancy between this version and the original IEEE  and  The  Open  Group
       Standard, the original IEEE and The Open Group Standard is the referee document. The orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003				      CLOSELOG(P)


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