CLOSELOG(3)                POSIX Programmer's Manual               CLOSELOG(3)



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

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 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 mm conversion specifier character is
       not just %%mm, 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.

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 ""TThhiissisaamessage" 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);

APPLICATION USAGE
       None.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       fprintf()

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

COPYRIGHT
       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(3)
