SYSLOG.CONF(5)

NAME
syslog.conf - syslogd(8) configuration file

DESCRIPTION
The syslog.conf file is the configuration file for the syslogd(8) program. It consists of blocks of lines separated by program specifications, with each line containing 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 characters or spaces.

Note that if you use spaces as separators, your syslog.conf might be incompatible with other Unices or Unix-like systems. This functionality was added for the ease of configuration (e.g. it is possible to cut-and-paste into syslog.conf ), and to avoid possible mistakes. This change however preserves backwards compatibility with the old style of the syslog.conf (i.e. tab characters only).

The Selectors function are encoded as a facility, a period (“”)., an optional set of comparison flags ([<=>]), 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, ftp, kern, lpr, mail, mark, news, ntp, syslog, user, uucp and local0 through local7. These keywords (with the exception of mark) correspond to the similar “LOG_” values specified to the openlog(3) and syslog(3) library routines.

The comparison flags may be used to specify exactly what is logged. The default set of comparison flags are “=>” (or, if you prefer, “>= ” ), which means that messages from the specified facility list of a priority level equal or greater than level will be logged.

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, info and debug. These keywords correspond to the similar “LOG_” values specified to the syslog library routine.

Each block of lines is separated from the previous block by a tag. The tag is a line beginning with #!prog or !prog (the former is for compatibility with the previous syslogd, if one is sharing syslog.conf files, for example) and each block will be associated with calls to syslog from that specific program. A tag for ``foo'' will also match any message logged by the kernel with the prefix ``foo: ''.

See syslog(3) for a further descriptions of both the facility and level keywords and their significance. It's preferred that selections be made on facility rather than program, since the latter can easily vary in a networked environment. In some cases, though, an appropriate facility simply doesn't exist.

If a received message matches the specified facility and is of the specified level (or a higher level), and the first word in the message after the date matches the program, 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 all levels or all programs.

The special facility “mark” receives a message at priority “info” every 20 minutes (see syslogd(8)). 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.

•   A hostname (preceded by an at (“@”) sign). Selected messages are forwarded to the syslogd program 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.

•   A vertical bar (“|”), followed by a command to pipe the selected messages to. The command is passed to a /bin/sh for evaluation, so usual shell metacharacters or input/output redirection can occur. (Note however that redirecting stdio(3) buffered output from the invoked command can cause additional delays, or even lost output data in case a logging subprocess exited with a signal.) The command itself runs with stdout and stderr redirected to /dev/null. Upon receipt of a SIGHUP, syslog.conf will close the pipe to the process. If the process didn't exit voluntarily, it will be sent a SIGTERM signal after a grace period of up to 60 seconds.

    The command will only be started once data arrives that should be piped to it. If it exited later, it will be restarted as necessary. So if it is desired that the subprocess should get exactly one line of input only (which can be very resource-consuming if there are a lot of messages flowing quickly), this can be achieved by exiting after just one line of input. If necessary, a script wrapper can be written to this effect.

    Unless the command is a full pipeline, it's probably useful to start the command with exec so that the invoking shell process does not wait for the command to complete. Warning: the process is started under the UID invoking syslogd(8), normally the superuser.

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

EXAMPLES

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
    # Log daemon messages at debug level only
    daemon.=debug						/var/log/daemon.debug
    # 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
    # Pipe all authentication messages to a filter.
    auth.*					|exec /usr/local/sbin/authfilter
    # Save ftpd transactions along with mail and news
    !ftpd
    *.*							/var/log/spoolerr
    # Log kernel firewall reports to a separate file
    !ipfw
    *.*							/var/log/ipfw

FILES
/etc/syslog.conf
    syslogd(8) configuration file

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

In networked environments, note that not all operating systems implement the same set of facilities. The facilities authpriv, cron, ftp, and ntp that are known to this implementation might be absent on the target system. Even worse, DEC UNIX uses facility number 10 (which is authpriv in this implementation) to log events for their AdvFS file system.

SEE ALSO
syslog(3), syslogd(8)