296 lines
7.3 KiB
Groff
296 lines
7.3 KiB
Groff
.\" Copyright (c) 1985, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)syslog.3 8.1 (Berkeley) 6/4/93
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.\" $FreeBSD$
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.\"
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.Dd July 21, 2015
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.Dt SYSLOG 3
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.Os
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.Sh NAME
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.Nm syslog ,
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.Nm vsyslog ,
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.Nm openlog ,
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.Nm closelog ,
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.Nm setlogmask
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.Nd control system log
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In syslog.h
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.In stdarg.h
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.Ft void
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.Fn syslog "int priority" "const char *message" "..."
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.Ft void
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.Fn vsyslog "int priority" "const char *message" "va_list args"
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.Ft void
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.Fn openlog "const char *ident" "int logopt" "int facility"
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.Ft void
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.Fn closelog void
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.Ft int
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.Fn setlogmask "int maskpri"
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.Sh DESCRIPTION
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The
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.Fn syslog
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function
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writes
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.Fa message
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to the system message logger.
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The message is then written to the system console, log files,
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logged-in users, or forwarded to other machines as appropriate.
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(See
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.Xr syslogd 8 . )
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.Pp
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The message is identical to a
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.Xr printf 3
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format string, except that
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.Ql %m
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is replaced by the current error
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message.
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(As denoted by the global variable
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.Va errno ;
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see
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.Xr strerror 3 . )
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A trailing newline is added if none is present.
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.Pp
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The
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.Fn vsyslog
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function
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is an alternate form in which the arguments have already been captured
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using the variable-length argument facilities of
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.Xr stdarg 3 .
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.Pp
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The message is tagged with
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.Fa priority .
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Priorities are encoded as a
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.Fa facility
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and a
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.Em level .
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The facility describes the part of the system
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generating the message.
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The level is selected from the following
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.Em ordered
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(high to low) list:
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.Bl -tag -width LOG_AUTHPRIV
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.It Dv LOG_EMERG
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A panic condition.
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This is normally broadcast to all users.
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.It Dv LOG_ALERT
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A condition that should be corrected immediately, such as a corrupted
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system database.
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.It Dv LOG_CRIT
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Critical conditions, e.g., hard device errors.
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.It Dv LOG_ERR
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Errors.
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.It Dv LOG_WARNING
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Warning messages.
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.It Dv LOG_NOTICE
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Conditions that are not error conditions,
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but should possibly be handled specially.
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.It Dv LOG_INFO
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Informational messages.
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.It Dv LOG_DEBUG
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Messages that contain information
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normally of use only when debugging a program.
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.El
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.Pp
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The
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.Fn openlog
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function
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provides for more specialized processing of the messages sent
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by
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.Fn syslog
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and
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.Fn vsyslog .
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The
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.Fa ident
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argument
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is a string that will be prepended to every message.
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The
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.Fa logopt
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argument
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is a bit field specifying logging options, which is formed by
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.Tn OR Ns 'ing
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one or more of the following values:
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.Bl -tag -width LOG_AUTHPRIV
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.It Dv LOG_CONS
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If
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.Fn syslog
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cannot pass the message to
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.Xr syslogd 8
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it will attempt to write the message to the console
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.Pq Dq Pa /dev/console .
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.It Dv LOG_NDELAY
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Open the connection to
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.Xr syslogd 8
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immediately.
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Normally the open is delayed until the first message is logged.
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Useful for programs that need to manage the order in which file
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descriptors are allocated.
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.It Dv LOG_PERROR
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Write the message to standard error output as well to the system log.
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.It Dv LOG_PID
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Log the process id with each message: useful for identifying
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instantiations of daemons.
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.El
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.Pp
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The
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.Fa facility
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argument encodes a default facility to be assigned to all messages
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that do not have an explicit facility encoded:
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.Bl -tag -width LOG_AUTHPRIV
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.It Dv LOG_AUTH
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The authorization system:
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.Xr login 1 ,
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.Xr su 1 ,
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.Xr getty 8 ,
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etc.
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.It Dv LOG_AUTHPRIV
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The same as
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.Dv LOG_AUTH ,
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but logged to a file readable only by
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selected individuals.
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.It Dv LOG_CONSOLE
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Messages written to
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.Pa /dev/console
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by the kernel console output driver.
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.It Dv LOG_CRON
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The cron daemon:
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.Xr cron 8 .
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.It Dv LOG_DAEMON
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System daemons, such as
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.Xr routed 8 ,
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that are not provided for explicitly by other facilities.
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.It Dv LOG_FTP
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The file transfer protocol daemons:
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.Xr ftpd 8 ,
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.Xr tftpd 8 .
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.It Dv LOG_KERN
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Messages generated by the kernel.
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These cannot be generated by any user processes.
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.It Dv LOG_LPR
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The line printer spooling system:
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.Xr lpr 1 ,
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.Xr lpc 8 ,
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.Xr lpd 8 ,
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etc.
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.It Dv LOG_MAIL
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The mail system.
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.It Dv LOG_NEWS
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The network news system.
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.It Dv LOG_NTP
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The network time protocol system.
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.It Dv LOG_SECURITY
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Security subsystems, such as
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.Xr ipfw 4 .
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.It Dv LOG_SYSLOG
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Messages generated internally by
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.Xr syslogd 8 .
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.It Dv LOG_USER
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Messages generated by random user processes.
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This is the default facility identifier if none is specified.
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.It Dv LOG_UUCP
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The uucp system.
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.It Dv LOG_LOCAL0
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Reserved for local use.
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Similarly for
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.Dv LOG_LOCAL1
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through
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.Dv LOG_LOCAL7 .
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.El
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.Pp
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The
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.Fn closelog
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function
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can be used to close the log file.
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.Pp
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The
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.Fn setlogmask
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function
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sets the log priority mask to
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.Fa maskpri
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and returns the previous mask.
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Calls to
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.Fn syslog
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with a priority not set in
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.Fa maskpri
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are rejected.
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The mask for an individual priority
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.Fa pri
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is calculated by the macro
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.Fn LOG_MASK pri ;
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the mask for all priorities up to and including
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.Fa toppri
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is given by the macro
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.Fn LOG_UPTO toppri ; .
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The default allows all priorities to be logged.
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.Sh RETURN VALUES
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The routines
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.Fn closelog ,
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.Fn openlog ,
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.Fn syslog
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and
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.Fn vsyslog
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return no value.
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.Pp
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The routine
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.Fn setlogmask
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always returns the previous log mask level.
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.Sh EXAMPLES
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.Bd -literal -offset indent -compact
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syslog(LOG_ALERT, "who: internal error 23");
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openlog("ftpd", LOG_PID | LOG_NDELAY, LOG_FTP);
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setlogmask(LOG_UPTO(LOG_ERR));
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syslog(LOG_INFO, "Connection from host %d", CallingHost);
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syslog(LOG_INFO|LOG_LOCAL2, "foobar error: %m");
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.Ed
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.Sh SEE ALSO
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.Xr logger 1 ,
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.Xr syslogd 8
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.Sh HISTORY
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These
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functions appeared in
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.Bx 4.2 .
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.Sh BUGS
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Never pass a string with user-supplied data as a format without using
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.Ql %s .
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An attacker can put format specifiers in the string to mangle your stack,
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leading to a possible security hole.
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This holds true even if the string was built using a function like
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.Fn snprintf ,
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as the resulting string may still contain user-supplied conversion specifiers
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for later interpolation by
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.Fn syslog .
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.Pp
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Always use the proper secure idiom:
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.Pp
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.Dl syslog(priority, "%s", string);
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