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.\"	@(#)syslog.3	6.8 (Berkeley) %G%
.\"
.TH SYSLOG 3 ""
.UC 5
.SH NAME
syslog, openlog, closelog, setlogmask \- control system log
.SH SYNOPSIS
.B "#include <syslog.h>
.PP
.B "openlog(ident, logopt, facility)
.br
.B "char *ident;
.PP
.B "syslog(priority, message, parameters ... )
.br
.B "int priority;
.br
.B "char *message;
.PP
.B "#include <varargs.h>
.br
.B "vsyslog(priority, message, args)
.br
.B "int priority;
.br
.B "char *message;
.br
.B "va_list args;
.PP
.B "closelog()
.PP
.B "setlogmask(maskpri)
.SH DESCRIPTION
.I Syslog
arranges to write
.I message
onto the system log maintained by
.IR syslogd (8).
The message is tagged with
.IR priority .
The message looks like a
.IR printf (3)
string except that
.B %m
is replaced by the current error message (collected from
.IR 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
.IR varargs (3),
is available under the name
.IR vsyslog .
.PP
This message will be read by
.IR syslogd (8)
and written to the system console, log files, or forwarded to
.I syslogd
on another host as appropriate.
.PP
Priorities are encoded as a
.I facility
and a
.IR level .
The facility describes the part of the system
generating the message.
The level is selected from an ordered list:
.IP LOG_EMERG \w'LOG_WARNING'u+3
A panic condition.
This is normally broadcast to all users.
.IP LOG_ALERT \w'LOG_WARNING'u+3
A condition that should be corrected immediately,
such as a corrupted system database.
.IP LOG_CRIT \w'LOG_WARNING'u+3
Critical conditions,
e.g., hard device errors.
.IP LOG_ERR \w'LOG_WARNING'u+3
Errors.
.IP LOG_WARNING \w'LOG_WARNING'u+3
Warning messages.
.IP LOG_NOTICE \w'LOG_WARNING'u+3
Conditions that are not error conditions,
but should possibly be handled specially.
.IP LOG_INFO \w'LOG_WARNING'u+3
Informational messages.
.IP LOG_DEBUG \w'LOG_WARNING'u+3
Messages that contain information
normally of use only when debugging a program.
.PP
If
.I syslog
cannot pass the message to
.IR syslogd ,
it will attempt to write the message on
.I /dev/console
if the LOG_CONS option is set (see below).
.PP
If special processing is needed,
.I openlog
can be called to initialize the log file.
The parameter
.I ident
is a string that is prepended to every message.
.I Logopt
is a bit field indicating logging options.
Current values for
.I logopt
are:
.IP LOG_PID \w'LOG_WARNING'u+3
log the process id with each message:
useful for identifying instantiations of daemons.
.IP LOG_CONS \w'LOG_WARNING'u+3
Force writing messages to the console if unable to send it to
.I syslogd.
This option is safe to use in daemon processes that have no controlling
terminal since
.I syslog
will fork before opening the console.
.IP LOG_NDELAY \w'LOG_WARNING'u+3
Open the connection to
.I 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.
.IP LOG_NOWAIT \w'LOG_WARNING'u+3
Don't wait for children forked to log messages on the console.
This option should be used by processes that enable notification
of child termination via SIGCHLD, as
.I syslog
may otherwise block waiting for a child whose exit status has already
been collected.
.PP
The
.I facility
parameter encodes a default facility to be assigned to all messages
that do not have an explicit facility encoded:
.IP LOG_KERN \w'LOG_WARNING'u+3
Messages generated by the kernel.
These cannot be generated by any user processes.
.IP LOG_USER \w'LOG_WARNING'u+3
Messages generated by random user processes.
This is the default facility identifier if none is specified.
.IP LOG_MAIL \w'LOG_WARNING'u+3
The mail system.
.IP LOG_DAEMON \w'LOG_WARNING'u+3
System daemons, such as
.IR ftpd (8),
.IR routed (8),
etc.
.IP LOG_AUTH \w'LOG_WARNING'u+3
The authorization system:
.IR login (1),
.IR su (1),
.IR getty (8),
etc.
.IP LOG_LPR \w'LOG_WARNING'u+3
The line printer spooling system:
.IR lpr (1),
.IR lpc (8),
.IR lpd (8),
etc.
.IP LOG_LOCAL0 \w'LOG_WARNING'u+3
Reserved for local use.
Similarly for LOG_LOCAL1 through LOG_LOCAL7.
.PP
.I Closelog
can be used to close the log file.
.PP
.I Setlogmask
sets the log priority mask to
.I maskpri
and returns the previous mask.
Calls to
.I syslog
with a priority not set in
.I maskpri
are rejected.
The mask for an individual priority
.I pri
is calculated by the macro LOG_MASK(\fIpri\fP);
the mask for all priorities up to and including
.I toppri
is given by the macro LOG_UPTO(\fItoppri\fP).
The default allows all priorities to be logged.
.SH EXAMPLES
.nf
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");
.fi
.SH "SEE ALSO"
logger(1),
syslogd(8)