SYSLOG.CONF(5) Linux System Administration SYSLOG.CONF(5)
NAME
syslog.conf - syslogd(8) configuration file
DESCRIPTION
The syslog.conf file is the main configuration file for the syslogd(8) which logs
system messages on *nix systems. This file specifies rules for logging. For spe
cial features see the sysklogd(8) manpage.
Every rule consists of two fields, a selector field and an action field. These
two fields are separated by one or more spaces or tabs. The selector field speci
fies a pattern of facilities and priorities belonging to the specified action.
Lines starting with a hash mark (``#'') and empty lines are ignored.
This release of syslogd is able to understand an extended syntax. One rule can be
divided into several lines if the leading line is terminated with an backslash
(``\'').
SELECTORS
The selector field itself again consists of two parts, a facility and a priority,
separated by a period (``.''). Both parts are case insensitive and can also be
specified as decimal numbers, but don't do that, you have been warned. Both
facilities and priorities are described in syslog(3). The names mentioned below
correspond to the similar LOG_-values in /usr/include/syslog.h.
The facility is one of the following keywords: auth, authpriv, cron, daemon, kern,
lpr, mail, mark, news, security (same as auth), syslog, user, uucp and local0
through local7. The keyword security should not be used anymore and mark is only
for internal use and therefore should not be used in applications. Anyway, you
may want to specify and redirect these messages here. The facility specifies the
subsystem that produced the message, i.e. all mail programs log with the mail
facility (LOG_MAIL) if they log using syslog.
The priority is one of the following keywords, in ascending order: debug, info,
notice, warning, warn (same as warning), err, error (same as err), crit, alert,
emerg, panic (same as emerg). The keywords error, warn and panic are deprecated
and should not be used anymore. The priority defines the severity of the message
The behavior of the original BSD syslogd is that all messages of the specified
priority and higher are logged according to the given action. This syslogd(8)
behaves the same, but has some extensions.
In addition to the above mentioned names the syslogd(8) understands the following
extensions: An asterisk (``*'') stands for all facilities or all priorities,
depending on where it is used (before or after the period). The keyword none
stands for no priority of the given facility.
You can specify multiple facilities with the same priority pattern in one state
ment using the comma (``,'') operator. You may specify as much facilities as you
want. Remember that only the facility part from such a statement is taken, a pri
ority part would be skipped.
Multiple selectors may be specified for a single action using the semicolon
(``;'') separator. Remember that each selector in the selector field is capable
to overwrite the preceding ones. Using this behavior you can exclude some priori
ties from the pattern.
This syslogd(8) has a syntax extension to the original BSD source, that makes its
use more intuitively. You may precede every priority with an equation sign
(``='') to specify only this single priority and not any of the above. You may
also (both is valid, too) precede the priority with an exclamation mark (``!'') to
ignore all that priorities, either exact this one or this and any higher priority.
If you use both extensions than the exclamation mark must occur before the equa
tion sign, just use it intuitively.
ACTIONS
The action field of a rule describes the abstract term ``logfile''. A ``logfile''
need not to be a real file, btw. The syslogd(8) provides the following actions.
Regular File
Typically messages are logged to real files. The file has to be specified with
full pathname, beginning with a slash ``/''.
You may prefix each entry with the minus ``-'' sign to omit syncing the file after
every logging. Note that you might lose information if the system crashes right
behind a write attempt. Nevertheless this might give you back some performance,
especially if you run programs that use logging in a very verbose manner.
Named Pipes
This version of syslogd(8) has support for logging output to named pipes (fifos).
A fifo or named pipe can be used as a destination for log messages by prepending a
pipe symbol (``|'') to the name of the file. This is handy for debugging. Note
that the fifo must be created with the mkfifo(1) command before syslogd(8) is
started.
Terminal and Console
If the file you specified is a tty, special tty-handling is done, same with
/dev/console.
Remote Machine
This syslogd(8) provides full remote logging, i.e. is able to send messages to a
remote host running syslogd(8) and to receive messages from remote hosts. The
remote host won't forward the message again, it will just log them locally. To
forward messages to another host, prepend the hostname with the at sign (``@'').
Using this feature you're able to control all syslog messages on one host, if all
other machines will log remotely to that. This tears down administration needs.
List of Users
Usually critical messages are also directed to ``root'' on that machine. You can
specify a list of users that shall get the message by simply writing the login.
You may specify more than one user by separating them with commas (``,''). If
they're logged in they get the message. Don't think a mail would be sent, that
might be too late.
Everyone logged on
Emergency messages often go to all users currently online to notify them that
something strange is happening with the system. To specify this wall(1)-feature
use an asterisk (``*'').
EXAMPLES
Here are some example, partially taken from a real existing site and configura
tion. Hopefully they rub out all questions to the configuration, if not, drop me
(Joey) a line.
# Store critical stuff in critical
#
*.=crit;kern.none /var/adm/critical
This will store all messages with the priority crit in the file /var/adm/critical,
except for any kernel message.
# Kernel messages are first, stored in the kernel
# file, critical messages and higher ones also go
# to another host and to the console
#
kern.* /var/adm/kernel
kern.crit @finlandia
kern.crit /dev/console
kern.info;kern.!err /var/adm/kernel-info
The first rule direct any message that has the kernel facility to the file
/var/adm/kernel.
The second statement directs all kernel messages of the priority crit and higher
to the remote host finlandia. This is useful, because if the host crashes and the
disks get irreparable errors you might not be able to read the stored messages.
If they're on a remote host, too, you still can try to find out the reason for the
crash.
The third rule directs these messages to the actual console, so the person who
works on the machine will get them, too.
The fourth line tells the syslogd to save all kernel messages that come with pri
orities from info up to warning in the file /var/adm/kernel-info. Everything from
err and higher is excluded.
# The tcp wrapper loggs with mail.info, we display
# all the connections on tty12
#
mail.=info /dev/tty12
This directs all messages that uses mail.info (in source LOG_MAIL | LOG_INFO) to
/dev/tty12, the 12th console. For example the tcpwrapper tcpd(8) uses this as
it's default.
# Store all mail concerning stuff in a file
#
mail.*;mail.!=info /var/adm/mail
This pattern matches all messages that come with the mail facility, except for the
info priority. These will be stored in the file /var/adm/mail.
# Log all mail.info and news.info messages to info
#
mail,news.=info /var/adm/info
This will extract all messages that come either with mail.info or with news.info
and store them in the file /var/adm/info.
# Log info and notice messages to messages file
#
*.=info;*.=notice;\
mail.none /var/log/messages
This lets the syslogd log all messages that come with either the info or the
notice facility into the file /var/log/messages, except for all messages that use
the mail facility.
# Log info messages to messages file
#
*.=info;\
mail,news.none /var/log/messages
This statement causes the syslogd to log all messages that come with the info pri
ority to the file /var/log/messages. But any message coming either with the mail
or the news facility will not be stored.
# Emergency messages will be displayed using wall
#
*.=emerg *
This rule tells the syslogd to write all emergency messages to all currently
logged in users. This is the wall action.
# Messages of the priority alert will be directed
# to the operator
#
*.alert root,joey
This rule directs all messages with a priority of alert or higher to the terminals
of the operator, i.e. of the users ``root'' and ``joey'' if they're logged in.
# to the operator
#
*.alert root,joey
This rule directs all messages with a priority of alert or higher to the terminals
of the operator, i.e. of the users ``root'' and ``joey'' if they're logged in.
*.* @finlandia
This rule would redirect all messages to a remote host called finlandia. This is
useful especially in a cluster of machines where all syslog messages will be
stored on only one machine.
CONFIGURATION FILE SYNTAX DIFFERENCES
Syslogd uses a slightly different syntax for its configuration file than the orig
inal BSD sources. Originally all messages of a specific priority and above were
forwarded to the log file. The modifiers ``='', ``!'' and ``-'' were added to
make the syslogd more flexible and to use it in a more intuitive manner.
The original BSD syslogd doesn't understand spaces as separators between the
selector and the action field.
FILES
/etc/syslog.conf
Configuration file for syslogd
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.
SEE ALSO
sysklogd(8), klogd(8), logger(1), syslog(2), syslog(3)
AUTHORS
The syslogd is taken from BSD sources, Greg Wettstein (greg@wind.enjellic.com)
performed the port to Linux, Martin Schulze (joey@linux.de) made some bugfixes and
added some new features.
Version 1.3 1 January 1998