closelog(3p) — Linux manual page


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 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>

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.1‐2017, syslog.h(0p)

COPYRIGHT         top

       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 .

       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               2017                      CLOSELOG(3P)

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