SYSLOG(3)SYSLOG(3)NAME
syslog, openlog, closelog, setlogmask, vsyslog - control system log
SYNOPSIS
#include <syslog.h>
openlog(ident, logopt, facility)
char *ident;
syslog(priority, message, parameters ... )
int priority;
char *message;
#include <varargs.h>
vsyslog(priority, message, args)
int priority;
char *message;
va_list args;
closelog()setlogmask(maskpri)DESCRIPTION
Syslog arranges to write message onto the system log maintained by sys‐
logd(8). The message is tagged with priority. The message looks like
a printf(3) string except that %m is replaced by the current error mes‐
sage (as referenced by errno). A trailing newline is added if needed.
An alternate form, in which the arguments have already been captured
using the variable-length argument facilities of varargs(3), is avail‐
able under the name vsyslog.
This message will be read by syslogd(8) and written to the system con‐
sole, log files, or forwarded to syslogd on another host as appropri‐
ate.
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_ALERT
A condition that should be corrected immediately, such as a cor‐
rupted system database.
LOG_CRIT
Critical conditions, e.g., hard device errors.
LOG_DEBUG
Messages that contain information normally of use only when
debugging a program.
LOG_EMERG
A panic condition. This is normally broadcast to all users.
LOG_ERR
Errors.
LOG_INFO
Informational messages.
LOG_NOTICE
Conditions that are not error conditions, but should possibly be
handled specially.
LOG_WARNING
Warning messages.
If syslog cannot pass the message to syslogd, it will attempt to write
the message to the console (``/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. Cur‐
rent values for logopt are:
LOG_CONS
If unable to send the message to syslogd, write it to the con‐
sole.
LOG_NDELAY
Open the connection to syslogd immediately. Normally the open
is delayed until the first message is logged. Useful for pro‐
grams that need to manage the order in which file descriptors
are allocated.
LOG_PERROR
Write the message to stderr as well to the system log.
LOG_PID
Log the process id with each message: useful for identifying
instantiations of daemons.
The facility parameter encodes a default facility to be assigned to all
messages that do not have an explicit facility encoded:
LOG_AUTH
The authorization system: login(1), su(1), getty(8), etc.
LOG_CRON
The clock daemon.
LOG_DAEMON
System daemons, such as ftpd(8), routed(8), etc, that are not
provided for explicitly by other facilities.
LOG_KERN
Messages generated by the kernel. These cannot be generated by
any user processes.
LOG_LPR
The line printer spooling system: lpr(1), lpc(8), lpd(8), etc.
LOG_MAIL
The mail system.
LOG_NEWS
The network news system.
LOG_SYSLOG
Messages generated internally by syslogd(8).
LOG_USER
Messages generated by random user processes. This is the
default facility identifier if none is specified.
LOG_UUCP
The uucp system.
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 previ‐
ous 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 June 23, 1990 SYSLOG(3)
