SYSLOG

Section: C Library Functions (3)
Updated: June 23, 1990
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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 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 (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 available under the name vsyslog.

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_ALERT: A condition that should be corrected immediately, such as a corrupted 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. Current values for logopt are:

LOG_CONS: If unable to send the message to syslogd, write it to 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_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 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");