syslog()

Write a message to the system log

Synopsis:

#include <syslog.h>

void syslog( int priority,
             const char * message, 
             ...)

void vsyslog( int priority,
              const char * message, 
              va_list args)

Library:

libc

Description:

The syslog() function writes message to the system message logger. The message is then written to the system console, log files, and logged-in users, or forwarded to other machines as appropriate. (See the syslogd command.)

The message is identical to a printf() format string, except that %m is replaced by the current error message (as denoted by the global variable errno). A trailing newline is added if none is present.

The vsyslog() function is an alternate form in which the arguments have already been captured using the variable-length argument facilities of <stdarg.h>.

Message levels

The message is tagged with priority. 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 the following list (ordered from high to low):

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 (for example, hard device errors).

LOG_ERR

General errors.

LOG_WARNING

Warning messages.

LOG_NOTICE

Conditions that aren't error conditions, but should possibly be specially handled.

LOG_INFO

Informational messages.

LOG_DEBUG

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

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");

Classification:

Standard Unix

See also:

closelog(), logger, openlog(), setlogmask(), syslogd