SYSLOG(3)SYSLOG(3)NAME
syslog, openlog, closelog, setlogmask - control system log
SYNOPSIS
#include <syslog.h>
openlog(ident, logopt, facility)
char *ident;
syslog(priority, message, parameters ... )
char *message;
closelog()setlogmask(maskpri)DESCRIPTION
Syslog arranges to write message onto the system log maintained by
syslogd(8). The message is tagged with priority. The message looks
like a printf(3) string except that %m is replaced by the current error
message (collected from errno). A trailing newline is added if needed.
This message will be read by syslogd(8) and written to the system
console, log files, or forwarded to syslogd on another host as
appropriate.
Priorities are encoded as a facility and a level. The facility
describes the part of the system generating the message. 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, e.g., 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.
If syslog cannot pass the message to syslogd, it will attempt 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 prepended to
every message. Logopt is a bit field indicating logging options.
Current 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. This option is safe to use in daemon
processes that have no controlling terminal since syslog
will fork before opening the console.
LOG_NDELAY Open the connection to syslogd immediately. Normally the
open is delayed until the first message is logged.
Useful for programs that need to manage the order in
which file descriptors are allocated.
LOG_NOWAIT Don't wait for children forked to log messages on the
console. This option should be used by processes that
enable notification of child termination via SIGCHLD, 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 that do not have an explicit facility encoded:
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(8), routed(8), etc.
LOG_AUTH The authorization system: login(1), su(1), getty(8), etc.
LOG_LPR The line printer spooling system: lpr(1), lpc(8), lpd(8),
etc.
LOG_LOCAL0 Reserved for local use. Similarly for LOG_LOCAL1 through
LOG_LOCAL7.
Closelog can be used to close 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
syslog(LOG_ALERT, "who: internal error 23");
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");
SEE ALSOlogger(1), syslogd(8)4.2 Berkeley Distribution May 15, 1986 SYSLOG(3)