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 main-
tained by syslogd(1M). The message is tagged with priority.
The message looks like a printf(3S) string except that %m is
replaced by the current error message (collected from
errno). A trailing newline is added if needed. This mes-
sage will be 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 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 immedi-
ately, 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
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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 other-
wise 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 facil-
ity encoded:
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 inetd(1M), routed(1M),
etc.
LOG_AUTH The authorization system: login(1), su(1),
getty(1M), etc.
LOG_LPR The line printer spooling system: lpr(1),
lpd(1M), etc.
LOG_LOCAL0 Reserved for local use. Similarly for
LOG_LOCAL1 through LOG_LOCAL7.
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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 prior-
ity 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 priori-
ties 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 ALSO
logger(1), syslogd(1M)
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