syslog.conf -- syslogd(8) configuration file
The syslog.conf file is the configuration file for the syslogd(8) program.
It consists of blocks of lines separated by program and hostname
specifications (separations appear along on the line), 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(8) 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 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 syslog.conf (i.e.
tab characters only).
The selectors 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, console, cron, daemon,
ftp, kern, lpr, mail, mark, news, ntp, security, syslog, user, uucp and
local0 through local7. These keywords (with the exception of mark) correspond
to 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 comparison is ``=>'' (or, if you prefer, ``>=''), which means
that messages from the specified facility list, and of a priority level
equal to or greater than level will be logged. Comparison flags beginning
with ``!'' will have their logical sense inverted. Thus ``!=info''
means all levels except info and ``!notice'' has the same meaning as
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 similar
``LOG_'' values specified to the syslog(3) library routine.
Each block of lines is separated from the previous block by a program or
hostname specification. A block will only log messages corresponding to
the most recent program and hostname specifications given. Thus, with a
block which selects `ppp' as the program, directly followed by a block
that selects messages from the hostname `dialhost', the second block will
only log messages from the ppp(8) program on dialhost.
A program specification 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 the following blocks will be associated
with calls to syslog(3) from that specific program. A program specification
for `foo' will also match any message logged by the kernel with
the prefix `foo: '. The `#!+prog' or `!+prog' specification works just
like the previous one, and the `#!-prog' or `!-prog' specification will
match any message but the ones from that program. Multiple programs may
be listed, separated by commas: `!prog1,prog2' matches messages from
either program, while `!-prog1,prog2' matches all messages but those from
`prog1' or `prog2'.
A hostname specification of the form `#+hostname' or `+hostname' means
the following blocks will be applied to messages received from the specified
hostname. Alternatively, the hostname specification `#-hostname' or
`-hostname' causes the following blocks to be applied to messages from
any host but the one specified. If the hostname is given as `@', the
local hostname will be used. As for program specifications, multiple
comma-seprarated values may be specified for hostname specifications.
A program or hostname specification may be reset by giving the program or
hostname as `*'.
See syslog(3) for 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
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:
+o A pathname (beginning with a leading slash). Selected messages are
appended to the file.
+o A hostname (preceded by an at (``@'') sign). Selected messages are
forwarded to the syslogd(8) program on the named host.
+o A comma separated list of users. Selected messages are written to
those users if they are logged in.
+o An asterisk. Selected messages are written to all logged-in users.
+o A vertical bar (``|''), followed by a command to pipe the selected
messages to. The command is passed to sh(1) 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, syslogd(8) 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.
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!
# Log anything (except mail) of level info or higher.
# Don't log private authentication messages!
# Log daemon messages at debug level only
# The authpriv file has restricted access.
# Log all the mail messages in one place.
# Everybody gets emergency messages, plus log them on another
# Root and Eric get alert and higher messages.
# Save mail and news errors of level err and higher in a
# special file.
# Pipe all authentication messages to a filter.
auth.* |exec /usr/local/sbin/authfilter
# Save ftpd transactions along with mail and news
# Log all security messages to a separate file.
# Log all writes to /dev/console to a separate file.
The ``kern'' facility is usually reserved for messages generated by the
local kernel. Other messages logged with facility ``kern'' are usually
translated to facility ``user''. This translation can be disabled; see
syslogd(8) for details.
/etc/syslog.conf syslogd(8) configuration file
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.
FreeBSD 5.2.1 June 9, 1993 FreeBSD 5.2.1 [ Back ]