This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface

       None.

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for  Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are most likely to have  been  introduced
       during   the   conversion  of  the  source  files  to  man  page  format.  To  report  such  errors,  see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                                   2017                                      CLOSELOG(3POSIX)

       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 specification %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  specification  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 facility 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 database.

       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. Possible 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 syslog().  The  ident
       argument  is  a string that is prepended to every message. The logopt argument 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 processes.

       LOG_CONS    Write messages to the system console if they cannot be sent  to  the  logging  facility.  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  notification  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 arguments are defined
       in the <syslog.h> header.

       No errors are defined.

       Thefollowingsectionsareinformative.

Usingopenlog()
       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);

   Usingsetlogmask()
       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);

   Usingsyslog
       The following example sends the message "Thisisamessage" to the default  logging  facility,  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);

       None.

       closelog, openlog, setlogmask, syslog — control system log

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of this interface
       may differ (consult the corresponding Linux manual page for details of Linux behavior), or the  interface
       may not be implemented on Linux.

       None.

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

fprintf()

       The Base Definitions volume of POSIX.1‐2017, <syslog.h>

       #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 */);