sysklogd/syslog.conf.5

.\" syslog.conf - syslogd(8) configuration file
.\" Copyright (c) 1995,2006  Joey Schulze <joey@infodrom.org>
.\" 
.\" This file is part of the sysklogd package, a kernel and system log daemon.
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.TH SYSLOG.CONF 5 "30 November 2006" "Version 1.3" "Linux System Administration"
.SH NAME
syslog.conf \- syslogd(8) configuration file
.SH DESCRIPTION
The
.I syslog.conf
file is the main configuration file for the
.BR syslogd (8)
which logs system messages on *nix systems.  This file specifies rules
for logging.  For special features see the
.BR sysklogd (8)
manpage.

Every rule consists of two fields, a 
.I selector
field and an
.I action 
field.  These two fields are separated by one or more spaces or
tabs.  The selector field specifies 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
.B 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
(``\\'').

.SH SELECTORS
The selector field itself again consists of two parts, a
.I facility
and a 
.IR 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 
.BR syslog (3).
The names mentioned below correspond to the similar 
.BR LOG_ -values
in
.IR /usr/include/syslog.h .

The
.I facility
is one of the following keywords:
.BR auth ", " authpriv ", " cron ", " daemon ", " ftp ", " kern ", " lpr ", "
.BR mail ", " mark ", " news ", " security " (same as " auth "), "
.BR syslog ", " user ", " uucp " and " local0 " through " local7 .
The keyword 
.B security
should not be used anymore and
.B 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
.I facility
specifies the subsystem that produced the message, i.e. all mail
programs log with the mail facility
.BR "" ( LOG_MAIL )
if they log using syslog.

In most cases anyone can log to any facility, so we rely on convention
for the correct facility to be chosen.  However, generally only the
kernel can log to the "kern" facility.  This is because the implementation
of openlog() and syslog() in glibc does not allow logging to the "kern"
facility.  Klogd circumvents this restriction when logging to syslogd
by reimplementing those functions itself.

The
.I priority
is one of the following keywords, in ascending order: 
.BR debug ", " info ", " notice ", " warning ", " warn " (same as "
.BR warning "), " err ", " error " (same as " err "), " crit ", "
.BR alert ", " emerg ", " panic " (same as " emerg ).
The keywords
.BR error ", " warn " and " panic
are deprecated and should not be used anymore.  The
.I 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
.BR syslogd (8)
behaves the same, but has some extensions.

In addition to the above mentioned names the
.BR 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
.B none
stands for no priority of the given facility.

You can specify multiple facilities with the same priority pattern in
one statement 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 priority part would be skipped.

Multiple selectors may be specified for a single
.I action
using the semicolon (``;'') separator.  Remember that each selector in
the 
.I selector
field is capable to overwrite the preceding ones.  Using this
behavior you can exclude some priorities from the pattern.

This 
.BR syslogd (8)
has a syntax extension to the original BSD source, which makes its use
more intuitive.  You may precede every priority with an equation sign
(``='') to specify that
.B syslogd
should only refer to this single priority and not this priority and
all higher priorities.

You may also precide the priority with an exclamation mark (``!'') if
you want
.B syslogd
to ignore this priority and all higher priorities.
You may even use both, the exclamation mark and the equation sign if
you want
.B syslogd
to ignore only this single priority.  If you use both extensions
than the exclamation mark must occur before the equation sign, just
use it intuitively.

.SH ACTIONS
The action field of a rule describes the abstract term
``logfile''.  A ``logfile'' need not to be a real file, btw.  The
.BR syslogd (8)
provides the following actions.

.SS 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.

.SS Named Pipes
This version of
.BR 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  
.BR mkfifo (1)
command  before
.BR syslogd (8)
is started.

.SS Terminal and Console
If the file you specified is a tty, special tty-handling is done, same
with
.IR /dev/console .

.SS Remote Machine
This 
.BR syslogd (8)
provides full remote logging, i.e. is able to send messages to a
remote host running 
.BR 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.

.SS 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.

.SS 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
.IR wall (1)-feature
use an asterisk (``*'').

.SH EXAMPLES
Here are some example, partially taken from a real existing site and
configuration.  Hopefully they rub out all questions to the
configuration, if not, drop me (Joey) a line.
.IP
.nf
# Store critical stuff in critical
#
*.=crit;kern.none            /var/adm/critical
.fi
.LP
This will store all messages with the priority
.B crit
in the file
.IR /var/adm/critical ,
except for any kernel message.

.IP
.nf
# 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
.fi
.LP
The first rule directs any message that has the kernel facility to the
file
.IR /var/adm/kernel .
(But recall that only the kernel itself can log to this facility.)

The second statement directs all kernel messages of the priority
.B 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 priorities from
.BR info " up to " warning
in the file
.IR /var/adm/kernel-info .
Everything from
.I err
and higher is excluded.

.IP
.nf
# The tcp wrapper loggs with mail.info, we display
# all the connections on tty12
#
mail.=info                   /dev/tty12
.fi
.LP
This directs all messages that uses 
.BR mail.info " (in source " LOG_MAIL " | " LOG_INFO )
to
.IR /dev/tty12 , 
the 12th console.  For example the tcpwrapper
.BR tcpd (8)
uses this as it's default.

.IP
.nf
# Store all mail concerning stuff in a file
#
mail.*;mail.!=info           /var/adm/mail
.fi
.LP
This pattern matches all messages that come with the
.B mail
facility, except for the
.B info
priority.  These will be stored in the file
.IR /var/adm/mail .

.IP
.nf
# Log all mail.info and news.info messages to info
#
mail,news.=info              /var/adm/info
.fi
.LP
This will extract all messages that come either with
.BR mail.info " or with " news.info 
and store them in the file
.IR /var/adm/info .

.IP
.nf
# Log info and notice messages to messages file
#
*.=info;*.=notice;\\
	mail.none  /var/log/messages
.fi
.LP
This lets the
.B syslogd
log all messages that come with either the
.BR info " or the " notice
priority into the file
.IR /var/log/messages ,
except for all messages that use the
.B mail
facility.

.IP
.nf
# Log info messages to messages file
#
*.=info;\\
	mail,news.none       /var/log/messages
.fi
.LP
This statement causes the
.B syslogd
to log all messages that come with the
.B info
priority to the file
.IR /var/log/messages .
But any message coming either with the
.BR mail " or the " news
facility will not be stored.

.IP
.nf
# Emergency messages will be displayed using wall
#
*.=emerg                     *
.fi
.LP
This rule tells the
.B syslogd
to write all emergency messages to all currently logged in users.  This
is the wall action.

.IP
.nf
# Messages of the priority alert will be directed
# to the operator
#
*.alert                      root,joey
.fi
.LP
This rule directs all messages with a priority of
.B alert
or higher to the terminals of the operator, i.e. of the users ``root''
and ``joey'' if they're logged in.

.IP
.nf
*.*                          @finlandia
.fi
.LP
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.

.SH CONFIGURATION FILE SYNTAX DIFFERENCES
.B Syslogd
uses a slightly different syntax for its configuration file than
the original 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
.B 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.
.SH FILES
.PD 0
.TP
.I /etc/syslog.conf
Configuration file for
.B syslogd

.SH 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.

.SH SEE ALSO
.BR sysklogd (8),
.BR klogd (8), 
.BR logger (1),
.BR syslog (2),
.BR syslog (3)

.SH AUTHORS
The
.B 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.