syslogd
*******

syslogd is a system service that provides error logging facility.  Messages are read from the UNIX domain socket /dev/log, from an Internet domain socket specified in /etc/services, and from the special device /dev/klog (to read kernel messages).

syslogd creates the file /var/run/syslog.pid, and stores its process id there.  This can be used to kill or reconfigure syslogd.

The message sent to syslogd should consist of a single line. The message can contain a priority code, which should be a preceding decimal number in angle braces, for example, <5>.  This priority code should map into the priorities defined in the include file sys/syslog.h.

Invoking
========

The options are as follows:

-f FILE
--rcfile=FILE
     Override configuration (the default file is /etc/syslog.conf).

--pidfile=FILE
     Override pidfile (the default file is /var/run/syslogd.pid).

-n
--no-detach
     Do not enter daemon mode.

-d
--debug
     Print debug information (implies -n).

-p FILE

--socket=FILE
     Override default UNIX domain socket /dev/log.

-a SOCKET
     Add UNIX socket to listen.  An unlimited number of sockets is allowed.

-r
--inet
     Receive remote messages via Internet domain socket.

--no-unixaf
     Do not listen on UNIX domain sockets (overrides -a and -p).

--no-klog
     Do not listen to kernel log device /dev/klog.

--no-forward
     Do not forward any messages (overrides -h).

-h

--hop
     Forward messages from remote hosts.

-m INTERVAL

--mark=INTERVAL
     Specify timestamp interval in logs (0 for no timestamps).

-l HOSTLIST
     Log hosts in HOSTLIST by their hostname. Multiple lists are allowed.

-s DOMAINLIST
     List of domains which should be stripped from the FQDN of hosts before logging their name.  Multiple lists are allowed.

Configuration file
==================

syslogd reads its configuration file when it starts up and whenever it receives a hangup signal.  The syslog.conf file is the configuration file for the syslogd program.  It consists of lines with two fields: the selector field which specifies the types of messages and priorities to which the line applies, and an action field which specifies the action to be taken if a message syslogd receives matches the selection criteria. The selector field is separated from the action field by one or more tab or space characters. A rule can be splitted in several lines if all lines except the last are terminated with a backslash \.

The Selectors function are encoded as a facility, a period (.), and a level, with no intervening white-space.  Both the facility and the level are case insensitive.

The facility describes the part of the system generating the message, and is one of the following keywords: auth, authpriv, cron, daemon, kern, lpr, mail, mark, news, syslog, user, uucp and local0 through local7.  These keywords (with the exception of mark) correspond to the similar LOG_ values specified to the openlog and syslog library routines. See Syslog (The GNU C Library Reference Manual), for details.

The level describes the severity of the message, and is a keyword from the following ordered list (higher to lower): emerg, alert, crit, err, warning, notice and debug.  These keywords correspond to the similar LOG_ values specified to the syslog library routine.

See syslog and vsyslog (The GNU C Library Reference Manual), for a further descriptions of both the facility and level keywords and their significance.

If a received message matches the specified facility and is of the specified level (or a higher level), the action specified in the action field will be taken.

Multiple selectors may be specified for a single action by separating them with semicolon (;) characters.  It is important to note, however, that each selector can modify the ones preceding it.

Multiple facilities may be specified for a single level by separating them with comma (,) characters.

An asterisk (*) can be used to specify all facilities or all levels.  Two asterisks (**) specifie all facilities not named previously in the configuration file.

By default, a level applies to all messages with the same or higher level. The equal (=) character can be prepended to a level to restrict this line of the configuration file to messages with the very same level.

An exclamation mark (!) prepended to a level or the asterisk means that this line of the configuration file does not apply to the specified level (and higher ones). In conjunction with the equal sign, you can exclude single levels as well.

The special facility mark receives a message at priority info every 20 minutes.  This is not enabled by a facility field containing an asterisk.

The special level none disables a particular facility.

The action field of each line specifies the action to be taken when the selector field selects a message.  There are five forms:

  * A pathname (beginning with a leading slash).  Selected messages are appended to the file.

     You may prepend a minus (-) to the path to omit syncing the file after each message log. This can cause data loss at system crashes, but increases performance for programs which use logging extensively.

  * A named pipe (fifo), beginning with a vertical bar (|) followed by a pathname. The pipe must be created with mkfifo(8) before syslogd reads its configuration file.  This feature is especially useful fo debugging.

  * A hostname (preceded by an at (@) sign).  Selected messages are forwarded to syslogd on the named host.

  * A comma separated list of users.  Selected messages are written to those users if they are logged in.

  * An asterisk.  Selected messages are written to all logged-in users.

     Blank lines and lines whose first non-blank character is a hash (#) character are ignored.

A configuration file might appear as follows:

     # Log all kernel messages, authentication messages of
     # level notice or higher and anything of level err or
     # higher to the console.
     # Don't log private authentication messages!
     *.err;kern.*;auth.notice;authpriv.none  /dev/console

     # Log anything (except mail) of level info or higher.
     # Don't log private authentication messages!
     *.info;mail.none;authpriv.none          /var/log/messages

     # The authpriv file has restricted access.
     authpriv.*                              /var/log/secure

     # Log all the mail messages in one place.
     mail.*                                  /var/log/maillog

     # Everybody gets emergency messages, plus log them on another
     # machine.
     *.emerg                                 *
     *.emerg                                 @arpa.berkeley.edu

     # Root and Eric get alert and higher messages.
     *.alert                                 root,eric

     # Save mail and news errors of level err and higher in a
     # special file.
     uucp,news.crit                          /var/log/spoolerr

The effects of multiple selectors are sometimes not intuitive.  For example mail.crit,*.err will select the mail facility messages at the level of err or higher, not at the level of crit or higher.