man-pages/man3p/syslog.3p

.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "CLOSELOG" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" closelog 
.SH NAME
closelog, openlog, setlogmask, syslog \- control system log
.SH SYNOPSIS
.LP
\fB#include <syslog.h>
.br
.sp
void closelog(void);
.br
void openlog(const char *\fP\fIident\fP\fB, int\fP \fIlogopt\fP\fB,
int\fP \fIfacility\fP\fB);
.br
int setlogmask(int\fP \fImaskpri\fP\fB);
.br
void syslog(int\fP \fIpriority\fP\fB, const char *\fP\fImessage\fP\fB,
\&... /*\fP \fIarguments\fP \fB*/); \fP
\fB
.br
\fP
.SH DESCRIPTION
.LP
The \fIsyslog\fP() 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.
.LP
The message body is generated from the \fImessage\fP and following
arguments in the same manner as if these were arguments to
\fIprintf\fP(), except that the additional conversion specification
\fB%m\fP shall be
recognized; it shall convert no arguments, shall cause the output
of the error message string associated with the value of
\fIerrno\fP on entry to \fIsyslog\fP(), and may be mixed with argument
specifications of the \fB"%\fP\fIn\fP\fB$"\fP form.
If a complete conversion specification with the \fBm\fP conversion
specifier character is not just \fB%m\fP , the behavior is
undefined. A trailing <newline> may be added if needed.
.LP
Values of the \fIpriority\fP 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.
.LP
Possible values of severity level include:
.TP 7
LOG_EMERG
A panic condition.
.TP 7
LOG_ALERT
A condition that should be corrected immediately, such as a corrupted
system database.
.TP 7
LOG_CRIT
Critical conditions, such as hard device errors.
.TP 7
LOG_ERR
Errors.
.TP 7
LOG_WARNING
.sp
Warning messages.
.TP 7
LOG_NOTICE
Conditions that are not error conditions, but that may require special
handling.
.TP 7
LOG_INFO
Informational messages.
.TP 7
LOG_DEBUG
Messages that contain information normally of use only when debugging
a program.
.sp
.LP
The facility indicates the application or system component generating
the message. Possible facility values include:
.TP 7
LOG_USER
Messages generated by arbitrary processes. This is the default facility
identifier if none is specified.
.TP 7
LOG_LOCAL0
Reserved for local use.
.TP 7
LOG_LOCAL1
Reserved for local use.
.TP 7
LOG_LOCAL2
Reserved for local use.
.TP 7
LOG_LOCAL3
Reserved for local use.
.TP 7
LOG_LOCAL4
Reserved for local use.
.TP 7
LOG_LOCAL5
Reserved for local use.
.TP 7
LOG_LOCAL6
Reserved for local use.
.TP 7
LOG_LOCAL7
Reserved for local use.
.sp
.LP
The \fIopenlog\fP() function shall set process attributes that affect
subsequent calls to \fIsyslog\fP(). The \fIident\fP
argument is a string that is prepended to every message. The \fIlogopt\fP
argument indicates logging options. Values for
\fIlogopt\fP are constructed by a bitwise-inclusive OR of zero or
more of the following:
.TP 7
LOG_PID
Log the process ID with each message. This is useful for identifying
specific processes.
.TP 7
LOG_CONS
Write messages to the system console if they cannot be sent to the
logging facility. The \fIsyslog\fP() function ensures that
the process does not acquire the console as a controlling terminal
in the process of writing the message.
.TP 7
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.
.TP 7
LOG_ODELAY
Delay open until \fIsyslog\fP() is called.
.TP 7
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 \fIsyslog\fP() may otherwise block waiting for a
child whose exit status has already been collected.
.sp
.LP
The \fIfacility\fP 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.
.LP
The \fIopenlog\fP() and \fIsyslog\fP() functions may allocate a file
descriptor. It is not necessary to call \fIopenlog\fP()
prior to calling \fIsyslog\fP().
.LP
The \fIcloselog\fP() function shall close any open file descriptors
allocated by previous calls to \fIopenlog\fP() or
\fIsyslog\fP().
.LP
The \fIsetlogmask\fP() function shall set the log priority mask for
the current process to \fImaskpri\fP and return the
previous mask. If the \fImaskpri\fP argument is 0, the current log
mask is not modified. Calls by the current process to
\fIsyslog\fP() with a priority not set in \fImaskpri\fP shall be rejected.
The default log mask allows all priorities to be
logged. A call to \fIopenlog\fP() is not required prior to calling
\fIsetlogmask\fP().
.LP
Symbolic constants for use as values of the \fIlogopt\fP, \fIfacility\fP,
\fIpriority\fP, and \fImaskpri\fP arguments are
defined in the \fI<syslog.h>\fP header.
.SH RETURN VALUE
.LP
The \fIsetlogmask\fP() function shall return the previous log priority
mask. The \fIcloselog\fP(), \fIopenlog\fP(), and
\fIsyslog\fP() functions shall not return a value.
.SH ERRORS
.LP
No errors are defined.
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.SS Using openlog()
.LP
The following example causes subsequent calls to \fIsyslog\fP() 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.
.sp
.RS
.nf

\fB#include <syslog.h>
.sp

char *ident = "Process demo";
int logopt = LOG_PID | LOG_CONS;
int facility = LOG_USER;
\&...
openlog(ident, logopt, facility);
\fP
.fi
.RE
.SS Using setlogmask()
.LP
The following example causes subsequent calls to \fIsyslog\fP() to
accept error messages, and to reject all other messages.
.sp
.RS
.nf

\fB#include <syslog.h>
.sp

int result;
int mask = LOG_MASK (LOG_ERR);
\&...
result = setlogmask(mask);
\fP
.fi
.RE
.SS Using syslog
.LP
The following example sends the message \fB"This is a message"\fP
to the default logging facility, marking the message as an
error message generated by random processes.
.sp
.RS
.nf

\fB#include <syslog.h>
.sp

char *message = "This is a message";
int priority = LOG_ERR | LOG_USER;
\&...
syslog(priority, message);
\fP
.fi
.RE
.SH APPLICATION USAGE
.LP
None.
.SH RATIONALE
.LP
None.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIprintf\fP() , the Base Definitions volume of IEEE\ Std\ 1003.1-2001,
\fI<syslog.h>\fP
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 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 .