# closelog

## PROLOG



           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



           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 **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.
    


## 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 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.
    


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