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

PROLOG         top

       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.

NAME         top

       closelog, openlog, setlogmask, syslog — control system log

SYNOPSIS         top

       #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         top

       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.

                   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

       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

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

RETURN VALUE         top

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

ERRORS         top

       No errors are defined.

       The following sections are informative.

EXAMPLES         top

   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 "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);



RATIONALE         top




SEE ALSO         top


       The Base Definitions volume of POSIX.1‐2008, syslog.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) 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 .

       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 .

IEEE/The Open Group                 2013                        CLOSELOG(3P)

Pages that refer to this page: syslog.h(0p)openlog(3p)setlogmask(3p)syslog(3p)