SYSLOG(3C)

NAME

syslog, openlog, closelog, setlogmask − control system log

SYNOPSIS

#include <syslog.h>

syslog(priority, message, parameters, ... )
int priority;
char *message;

openlog(ident, logopt, facility)
char *ident;
int logopt, facility;

closelog()

setlogmask(maskpri)

DESCRIPTION

Syslog writes a message onto the system log maintained by syslogd(1M). The message is tagged with priority. The message is similar to a printf(3S) format string except that %m is replaced by the error message associated with the current value of errno. A trailing newline is added if needed. This message is read by syslogd(1M) and written to the system console, log files, or forwarded to syslogd on another host as appropriate.

Priorities are encoded as a level and a facility. The level is selected from an ordered list:

LOG_EMERG A panic condition. This is normally broadcast to all users.

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 should possibly be handled specially.

LOG_INFO Informational messages.

LOG_DEBUG Messages that contain information normally of use only when debugging a program.

The facility describes the part of the system generating the message:

LOG_KERN Messages generated by the kernel. These cannot be generated by any user processes.

LOG_USER Messages generated by random user processes. This is the default facility identifier if none is specified.

LOG_MAIL The mail system.

LOG_DAEMON System daemons, such as ftpd(1M), rwhod(1M), etc.

LOG_AUTH The authorization system: login(1), su(1), getty(1M), etc.

LOG_LPR The line printer spooling system: lp(1), lpsched(1M), etc.

LOG_LOCAL0 Reserved for local use. Similarly for LOG_LOCAL1 through LOG_LOCAL7.

If syslog cannot pass the message to syslogd(1M), it attempts to write the message on /dev/console if the LOG_CONS option is set (see below).

If special processing is needed, openlog can be called to initialize the log file. The parameter ident is a string that is precedes every message. Logopt is a mask of bits indicating logging options. The values for logopt are:

LOG_PID Log the process ID with each message; useful for identifying instantiations of daemons.

LOG_CONS Force writing messages to the console if unable to send it to syslogd(1M). This option is safe to use in daemon processes that have no controlling terminal, because syslog forks before opening the console.

LOG_NDELAY Open the connection to syslogd(1M) 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_NOWAIT Do not wait for children forked to log messages on the console. This option should be used by processes that enable notification of child termination via SIGCLD, as syslog may otherwise block waiting for a child whose exit status has already been collected.

The facility parameter encodes a default facility to be assigned to all messages written subsequently by syslog with no explicit facility encoded.

Closelog closes the log file.

Setlogmask sets the log priority mask to maskpri and returns the previous mask. Calls to syslog with a priority not set in maskpri are rejected. The mask for an individual priority pri is calculated by the macro LOG_MASK(pri); the mask for all priorities up to and including toppri is given by the macro LOG_UPTO(toppri). The default allows all priorities to be logged.

EXAMPLES

This call to syslog logs a message regarding a corrupted who database:

syslog(LOG_ALERT, "who: internal error 23");

This example shows the use of openlog to set up special formatting for the ftp daemon:

openlog("ftpd", LOG_PID, LOG_DAEMON);
setlogmask(LOG_UPTO(LOG_ERR));
syslog(LOG_INFO, "Connection from host %d", CallingHost);
syslog(LOG_INFO|LOG_LOCAL2, "foobar error: %m");

WARNINGS

A call to syslog(3C) has no effect if the syslog daemon (syslogd(1M)) is not running on the system.

AUTHOR

Syslog was developed by the University of California, Berkeley.

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