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 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");

SEE ALSO
logger(1), syslogd(8)