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() passes message to syslogd(8), which logs it in an appropriate system log, writes it to the system console, forwards it to a list of users, or forwards it to the syslogd on another host over the network. The message is tagged with a priority of priority. The message looks like a printf(3V) string except that %m is replaced by the current error message (collected from errno). A trailing NEWLINE is added if needed.

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, such as hard device errors.

    LOG_ERR
        Errors.

    LOG_WARNING
        Warning messages.

    LOG_NOTICE
        Conditions that are not error conditions, but that may require special handling.

    LOG_INFO
        Informational messages.

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

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. This is useful for identifying specific daemon processes (for daemons that fork).

    LOG_CONS
        Write messages to the system console if they cannot be sent to syslogd. This option is safe to use in daemon processes that have no controlling terminal, since syslog() forks before opening the console.

    LOG_NDELAY
        Open the connection to syslogd immediately. Normally the open is delayed until the first message is logged. This is useful for programs that need to manage the order in which file descriptors are allocated.

    LOG_NOWAIT
        Do not wait for child processes that have been forked to log messages onto the console. This option should be used by processes that enable notification of child termination using SIGCHLD, since 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 already 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(8C), routed(8C), etc.

    LOG_AUTH
        The authorization system: login(1), su(1V), getty(8), etc.

    LOG_LPR
        The line printer spooling system: lpr(1), lpc(8), lpd(8), etc.

    LOG_NEWS
        Reserved for the USENET network news system.

    LOG_UUCP
        Reserved for the UUCP system; it does not currently use syslog.

    LOG_CRON
        The cron/at facility; crontab(1), at(1), cron(8), etc.

    LOG_LOCAL0-7
        Reserved for local use.

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
This call logs a message at priority LOG_ALERT:

    syslog(LOG_ALERT, "who: internal error 23");

The FTP daemon ftpd would make this call to openlog() to indicate that all messages it logs should have an identifying string of ftpd, should be treated by syslogd as other messages from system daemons are, should include the process ID of the process logging the message:

    openlog("ftpd", LOG_PID, LOG_DAEMON);

Then it would make the following call to setlogmask() to indicate that messages at priorities from LOG_EMERG through LOG_ERR should be logged, but that no messages at any other priority should be logged:

    setlogmask(LOG_UPTO(LOG_ERR));

Then, to log a message at priority LOG_INFO, it would make the following call to syslog:

    syslog(LOG_INFO, "Connection from host %d", CallingHost);

A locally-written utility could use the following call to syslog() to log a message at priority LOG_INFO to be treated by syslogd as other messages to the facility LOG_LOCAL2 are:

    syslog(LOG_INFO|LOG_LOCAL2, "error: %m");

SEE ALSO
at(1), crontab(1), logger(1), login(1), lpr(1), su(1V), printf(3V), syslog.conf(5), cron(8), ftpd(8C), getty(8), lpc(8), lpd(8), routed(8C), syslogd(8)