RSYSLOG.CONF(5) Linux System Administration RSYSLOG.CONF(5)
NAME
rsyslog.conf - rsyslogd(8) configuration file
DESCRIPTION
The rsyslog.conf file is the main configuration file for the rsyslogd(8) which logs system messages on *nix systems. This file specifies
rules for logging. For special features see the rsyslogd(8) manpage. Rsyslog.conf is backward-compatible with sysklogd's syslog.conf file.
So if you migrate from sysklogd you can rename it and it should work.
Note that this version of rsyslog ships with extensive documentation in html format. This is provided in the ./doc subdirectory and proba-
bly in a separate package if you installed rsyslog via a packaging system. To use rsyslog's advanced features, you need to look at the
html documentation, because the man pages only cover basic aspects of operation.
MODULES
Rsyslog has a modular design. Consequently, there is a growing number of modules. See the html documentation for their full description.
omsnmp SNMP trap output module
omgssapi
Output module for GSS-enabled syslog
ommysql
Output module for MySQL
omrelp Output module for the reliable RELP protocol (prevents message loss). For details, see below at imrelp and the html documentation.
It can be used like this:
*.* :omrelp:server:port
*.* :omrelp:192.168.0.1:2514 # actual sample
ompgsql
Output module for PostgreSQL
omlibdbi
Generic database output module (Firebird/Interbase, MS SQL, Sybase, SQLite, Ingres, Oracle, mSQL)
imfile Input module for text files
imudp Input plugin for UDP syslog. Replaces the deprecated -r option. Can be used like this:
$ModLoad imudp
$UDPServerRun 514
imtcp Input plugin for plain TCP syslog. Replaces the deprecated -t option. Can be used like this:
$ModLoad imtcp
$InputTCPServerRun 514
imrelp Input plugin for the RELP protocol. RELP can be used instead of UDP or plain TCP syslog to provide reliable delivery of syslog mes-
sages. Please note that plain TCP syslog does NOT provide truly reliable delivery, with it messages may be lost when there is a con-
nection problem or the server shuts down. RELP prevents message loss in those cases. It can be used like this:
$ModLoad imrelp
$InputRELPServerRun 2514
imgssapi
Input plugin for plain TCP and GSS-enable syslog
immark Support for mark messages
imklog Kernel logging. To include kernel log messages, you need to do
$ModLoad imklog
Please note that the klogd daemon is no longer necessary and consequently no longer provided by the rsyslog package.
imuxsock
Unix sockets, including the system log socket. You need to specify
$ModLoad imuxsock
in order to receive log messages from local system processes. This config directive should only left out if you know exactly what
you are doing.
BASIC STRUCTURE
Lines starting with a hash mark ('#') and empty lines are ignored. Rsyslog.conf should contain following sections (sorted by recommended
order in file):
Global directives
Global directives set some global properties of whole rsyslog daemon, for example size of main message queue ($MainMessageQueue-
Size), loading external modules ($ModLoad) and so on. All global directives need to be specified on a line by their own and must
start with a dollar-sign. The complete list of global directives can be found in html documentation in doc directory or online on
web pages.
Templates
Templates allow you to specify format of the logged message. They are also used for dynamic file name generation. They have to be
defined before they are used in rules. For more info about templates see TEMPLATES section of this manpage.
Output channels
Output channels provide an umbrella for any type of output that the user might want. They have to be defined before they are used
in rules. For more info about output channels see OUTPUT CHANNELS section of this manpage.
Rules (selector + action)
Every rule line 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 specifies a pattern of facilities and priorities belonging to the specified action.
SELECTORS
The selector field itself again consists of two parts, a facility and a priority, separated by a period ('.'). Both parts are case insensi-
tive 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. Rsyslogd behaves the same, but has some extensions.
In addition to the above mentioned names the rsyslogd(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 facil-
ity.
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 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 priorities from the pattern.
Rsyslogd has a syntax extension to the original BSD source, that makes its use more intuitively. You may precede every priority with an
equals 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 exten-
sions than the exclamation mark must occur before the equals sign, just use it intuitively.
ACTIONS
The action field of a rule describes what to do with the message. In general, message content is written to a kind of "logfile". But also
other actions might be done, like writing to a database table or forwarding to another host.
Regular file
Typically messages are logged to real files. The file has to be specified with full pathname, beginning with a slash ('/').
Example:
*.* /var/log/traditionalfile.log;RSYSLOG_TraditionalFileFormat # log to a file in the traditional format
Note: if you would like to use high-precision timestamps in your log files, just remove the ";RSYSLOG_TraditionalFormat". That will select
the default template, which, if not changed, uses RFC 3339 timestamps.
Example:
*.* /var/log/file.log # log to a file with RFC3339 timestamps
By default, files are not synced after earch write. To enable syncing of log files globally, use either the "$ActionFileEnableSync" direc-
tive or the "sync" parameter to omfile. Enabling this option degrades performance and it is advised not to enable syncing unless you know
what you are doing. To selectively disable syncing for certain files, you may prefix the file path with a minus sign ("-").
Named pipes
This version of rsyslogd(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 rsyslogd(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
There are three ways to forward message: the traditional UDP transport, which is extremely lossy but standard, the plain TCP based trans-
port which loses messages only during certain situations but is widely available and the RELP transport which does not lose messages but is
currently available only as part of rsyslogd 3.15.0 and above.
To forward messages to another host via UDP, prepend the hostname with the at sign ("@"). To forward it via plain tcp, prepend two at
signs ("@@"). To forward via RELP, prepend the string ":omrelp:" in front of the hostname.
Example:
*.* @192.168.0.1
In the example above, messages are forwarded via UDP to the machine 192.168.0.1, the destination port defaults to 514. Due to the nature of
UDP, you will probably lose some messages in transit. If you expect high traffic volume, you can expect to lose a quite noticeable number
of messages (the higher the traffic, the more likely and severe is message loss).
Sockets for forwarded messages can be bound to a specific device using the "device" option for the omfwd module.
Example:
action(type="omfwd" Target="192.168.0.1" Device="eth0" Port=514 Protocol="udp")
In the example above, messages are forwarded via UDP to the machine 192.168.0.1 at port 514 over the device eth0. TCP can be used by set-
ting Protocol to "tcp" in the above example.
For Linux with VRF support, the device option is used to specify the VRF to send messages.
If you would like to prevent message loss, use RELP:
*.* :omrelp:192.168.0.1:2514
Note that a port number was given as there is no standard port for relp.
Keep in mind that you need to load the correct input and output plugins (see "Modules" above).
Please note that rsyslogd offers a variety of options in regarding to remote forwarding. For full details, please see the html documenta-
tion.
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 sim-
ply writing ":omusrmsg:" followed by the login name. You may specify more than one user by separating them with commas (','). If they're
logged in they get the message (for example: ":omusrmsg:root,user1,user2").
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 ":omusrmsg:*".
Database table
This allows logging of the message to a database table. By default, a MonitorWare-compatible schema is required for this to work. You can
create that schema with the createDB.SQL file that came with the rsyslog package. You can also use any other schema of your liking - you
just need to define a proper template and assign this template to the action.
See the html documentation for further details on database logging.
Discard
If the discard action is carried out, the received message is immediately discarded. Discard can be highly effective if you want to filter
out some annoying messages that otherwise would fill your log files. To do that, place the discard actions early in your log files. This
often plays well with property-based filters, giving you great freedom in specifying what you do not want.
Discard is just the single 'stop' command with no further parameters.
Example:
*.* stop # discards everything.
Output channel
Binds an output channel definition (see there for details) to this action. Output channel actions must start with a $-sign, e.g. if you
would like to bind your output channel definition "mychannel" to the action, use "$mychannel". Output channels support template definitions
like all all other actions.
Shell execute
This executes a program in a subshell. The program is passed the template-generated message as the only command line parameter. Rsyslog
waits until the program terminates and only then continues to run.
Example:
^program-to-execute;template
The program-to-execute can be any valid executable. It receives the template string as a single parameter (argv[1]).
FILTER CONDITIONS
Rsyslog offers three different types "filter conditions":
* "traditional" severity and facility based selectors
* property-based filters
* expression-based filters
Selectors
Selectors are the traditional way of filtering syslog messages. They have been kept in rsyslog with their original syntax, because it is
well-known, highly effective and also needed for compatibility with stock syslogd configuration files. If you just need to filter based on
priority and facility, you should do this with selector lines. They are not second-class citizens in rsyslog and offer the best performance
for this job.
Property-Based Filters
Property-based filters are unique to rsyslogd. They allow to filter on any property, like HOSTNAME, syslogtag and msg.
A property-based filter must start with a colon in column 0. This tells rsyslogd that it is the new filter type. The colon must be followed
by the property name, a comma, the name of the compare operation to carry out, another comma and then the value to compare against. This
value must be quoted. There can be spaces and tabs between the commas. Property names and compare operations are case-sensitive, so "msg"
works, while "MSG" is an invalid property name. In brief, the syntax is as follows:
:property, [!]compare-operation, "value"
The following compare-operations are currently supported:
contains
Checks if the string provided in value is contained in the property
isequal
Compares the "value" string provided and the property contents. These two values must be exactly equal to match.
startswith
Checks if the value is found exactly at the beginning of the property value
regex
Compares the property against the provided regular expression.
Expression-Based Filters
See the html documentation for this feature.
TEMPLATES
Every output in rsyslog uses templates - this holds true for files, user messages and so on. Templates compatible with the stock syslogd
formats are hardcoded into rsyslogd. If no template is specified, we use one of these hardcoded templates. Search for "template_" in sys-
logd.c and you will find the hardcoded ones.
A template consists of a template directive, a name, the actual template text and optional options. A sample is:
$template MyTemplateName,"7Text %property% some more text
",<options>
The "$template" is the template directive. It tells rsyslog that this line contains a template. The backslash is an escape character. For
example, 7 rings the bell (this is an ASCII value),
is a new line. The set in rsyslog is a bit restricted currently.
All text in the template is used literally, except for things within percent signs. These are properties and allow you access to the con-
tents of the syslog message. Properties are accessed via the property replacer and it can for example pick a substring or do date-specific
formatting. More on this is the PROPERTY REPLACER section of this manpage.
To escape:
% = \%
= \ --> '' is used to escape (as in C)
$template TraditionalFormat,"%timegenerated% %HOSTNAME% %syslogtag%%msg%
"
Properties can be accessed by the property replacer (see there for details).
Please note that templates can also by used to generate selector lines with dynamic file names. For example, if you would like to split
syslog messages from different hosts to different files (one per host), you can define the following template:
$template DynFile,"/var/log/system-%HOSTNAME%.log"
This template can then be used when defining an output selector line. It will result in something like "/var/log/system-localhost.log"
Template options
The <options> part is optional. It carries options influencing the template as whole. See details below. Be sure NOT to mistake template
options with property options - the later ones are processed by the property replacer and apply to a SINGLE property, only (and not the
whole template).
Template options are case-insensitive. Currently defined are:
sql format the string suitable for a SQL statement in MySQL format. This will replace single quotes ("'") and the backslash char-
acter by their backslash-escaped counterpart ("'" and "") inside each field. Please note that in MySQL configuration, the
NO_BACKSLASH_ESCAPES mode must be turned off for this format to work (this is the default).
stdsql format the string suitable for a SQL statement that is to be sent to a standards-compliant sql server. This will replace sin-
gle quotes ("'") by two single quotes ("''") inside each field. You must use stdsql together with MySQL if in MySQL configu-
ration the NO_BACKSLASH_ESCAPES is turned on.
Either the sql or stdsql option MUST be specified when a template is used for writing to a database, otherwise injection might occur.
Please note that due to the unfortunate fact that several vendors have violated the sql standard and introduced their own escape methods,
it is impossible to have a single option doing all the work. So you yourself must make sure you are using the right format. If you choose
the wrong one, you are still vulnerable to sql injection.
Please note that the database writer *checks* that the sql option is present in the template. If it is not present, the write database
action is disabled. This is to guard you against accidental forgetting it and then becoming vulnerable to SQL injection. The sql option
can also be useful with files - especially if you want to import them into a database on another machine for performance reasons. However,
do NOT use it if you do not have a real need for it - among others, it takes some toll on the processing time. Not much, but on a really
busy system you might notice it ;)
The default template for the write to database action has the sql option set.
Template examples
Please note that the samples are split across multiple lines. A template MUST NOT actually be split across multiple lines.
A template that resembles traditional syslogd file output:
$template TraditionalFormat,"%timegenerated% %HOSTNAME%
%syslogtag%%msg:::drop-last-lf%
"
A template that tells you a little more about the message:
$template precise,"%syslogpriority%,%syslogfacility%,%timegenerated%,%HOSTNAME%,
%syslogtag%,%msg%
"
A template for RFC 3164 format:
$template RFC3164fmt,"<%PRI%>%TIMESTAMP% %HOSTNAME% %syslogtag%%msg%"
A template for the format traditionally used for user messages:
$template usermsg," XXXX%syslogtag%%msg%
"
And a template with the traditional wall-message format:
$template wallmsg,"
7Message from syslogd@%HOSTNAME% at %timegenerated%"
A template that can be used for writing to a database (please note the SQL template option)
$template MySQLInsert,"insert iut, message, receivedat values ('%iut%', '%msg:::UPPERCASE%', '%timegenerated:::date-mysql%') into
systemevents
", SQL
NOTE 1: This template is embedded into core application under name StdDBFmt , so you don't need to define it.
NOTE 2: You have to have MySQL module installed to use this template.
OUTPUT CHANNELS
Output Channels are a new concept first introduced in rsyslog 0.9.0. As of this writing, it is most likely that they will be replaced by
something different in the future. So if you use them, be prepared to change you configuration file syntax when you upgrade to a later
release.
Output channels are defined via an $outchannel directive. It's syntax is as follows:
$outchannel name,file-name,max-size,action-on-max-size
name is the name of the output channel (not the file), file-name is the file name to be written to, max-size the maximum allowed size and
action-on-max-size a command to be issued when the max size is reached. This command always has exactly one parameter. The binary is that
part of action-on-max-size before the first space, its parameter is everything behind that space.
Keep in mind that $outchannel just defines a channel with "name". It does not activate it. To do so, you must use a selector line (see
below). That selector line includes the channel name plus ":omfile:$" in front of it. A sample might be:
*.* :omfile:$mychannel
PROPERTY REPLACER
The property replacer is a core component in rsyslogd's output system. A syslog message has a number of well-defined properties (see
below). Each of this properties can be accessed and manipulated by the property replacer. With it, it is easy to use only part of a prop-
erty value or manipulate the value, e.g. by converting all characters to lower case.
Accessing Properties
Syslog message properties are used inside templates. They are accessed by putting them between percent signs. Properties can be modified by
the property replacer. The full syntax is as follows:
%propname:fromChar:toChar:options%
propname is the name of the property to access. It is case-sensitive.
Available Properties
msg the MSG part of the message (aka "the message" ;))
rawmsg the message exactly as it was received from the socket. Should be useful for debugging.
HOSTNAME
hostname from the message
FROMHOST
hostname of the system the message was received from (in a relay chain, this is the system immediately in front of us and not neces-
sarily the original sender)
syslogtag
TAG from the message
programname
the "static" part of the tag, as defined by BSD syslogd. For example, when TAG is "named[12345]", programname is "named".
PRI PRI part of the message - undecoded (single value)
PRI-text
the PRI part of the message in a textual form (e.g. "syslog.info")
IUT the monitorware InfoUnitType - used when talking to a MonitorWare backend (also for phpLogCon)
syslogfacility
the facility from the message - in numerical form
syslogfacility-text
the facility from the message - in text form
syslogseverity
severity from the message - in numerical form
syslogseverity-text
severity from the message - in text form
timegenerated
timestamp when the message was RECEIVED. Always in high resolution
timereported
timestamp from the message. Resolution depends on what was provided in the message (in most cases, only seconds)
TIMESTAMP
alias for timereported
PROTOCOL-VERSION
The contents of the PROTOCOL-VERSION field from IETF draft draft-ietf-syslog-protocol
STRUCTURED-DATA
The contents of the STRUCTURED-DATA field from IETF draft draft-ietf-syslog-protocol
APP-NAME
The contents of the APP-NAME field from IETF draft draft-ietf-syslog-protocol
PROCID The contents of the PROCID field from IETF draft draft-ietf-syslog-protocol
MSGID The contents of the MSGID field from IETF draft draft-ietf-syslog-protocol
$NOW The current date stamp in the format YYYY-MM-DD
$YEAR The current year (4-digit)
$MONTH The current month (2-digit)
$DAY The current day of the month (2-digit)
$HOUR The current hour in military (24 hour) time (2-digit)
$MINUTE
The current minute (2-digit)
Properties starting with a $-sign are so-called system properties. These do NOT stem from the message but are rather internally-generated.
Character Positions
FromChar and toChar are used to build substrings. They specify the offset within the string that should be copied. Offset counting starts
at 1, so if you need to obtain the first 2 characters of the message text, you can use this syntax: "%msg:1:2%". If you do not wish to
specify from and to, but you want to specify options, you still need to include the colons. For example, if you would like to convert the
full message text to lower case, use "%msg:::lowercase%". If you would like to extract from a position until the end of the string, you can
place a dollar-sign ("$") in toChar (e.g. %msg:10:$%, which will extract from position 10 to the end of the string).
There is also support for regular expressions. To use them, you need to place a "R" into FromChar. This tells rsyslog that a regular
expression instead of position-based extraction is desired. The actual regular expression must then be provided in toChar. The regular
expression must be followed by the string "--end". It denotes the end of the regular expression and will not become part of it. If you are
using regular expressions, the property replacer will return the part of the property text that matches the regular expression. An example
for a property replacer sequence with a regular expression is: "%msg:R:.*Sev:. (.*) [.*--end%"
Also, extraction can be done based on so-called "fields". To do so, place a "F" into FromChar. A field in its current definition is any-
thing that is delimited by a delimiter character. The delimiter by default is TAB (US-ASCII value 9). However, if can be changed to any
other US-ASCII character by specifying a comma and the decimal US-ASCII value of the delimiter immediately after the "F". For example, to
use comma (",") as a delimiter, use this field specifier: "F,44". If your syslog data is delimited, this is a quicker way to extract than
via regular expressions (actually, a *much* quicker way). Field counting starts at 1. Field zero is accepted, but will always lead to a
"field not found" error. The same happens if a field number higher than the number of fields in the property is requested. The field number
must be placed in the "ToChar" parameter. An example where the 3rd field (delimited by TAB) from the msg property is extracted is as fol-
lows: "%msg:F:3%". The same example with semicolon as delimiter is "%msg:F,59:3%".
Please note that the special characters "F" and "R" are case-sensitive. Only upper case works, lower case will return an error. There are
no white spaces permitted inside the sequence (that will lead to error messages and will NOT provide the intended result).
Property Options
Property options are case-insensitive. Currently, the following options are defined:
uppercase
convert property to lowercase only
lowercase
convert property text to uppercase only
drop-last-lf
The last LF in the message (if any), is dropped. Especially useful for PIX.
date-mysql
format as mysql date
date-rfc3164
format as RFC 3164 date
date-rfc3339
format as RFC 3339 date
escape-cc
replace control characters (ASCII value 127 and values less then 32) with an escape sequence. The sequence is "#<charval>" where
charval is the 3-digit decimal value of the control character. For example, a tabulator would be replaced by "#009".
space-cc
replace control characters by spaces
drop-cc
drop control characters - the resulting string will neither contain control characters, escape sequences nor any other replacement
character like space.
QUEUED OPERATIONS
Rsyslogd supports queued operations to handle offline outputs (like remote syslogd's or database servers being down). When running in
queued mode, rsyslogd buffers messages to memory and optionally to disk (on an as-needed basis). Queues survive rsyslogd restarts.
It is highly suggested to use remote forwarding and database writing in queued mode, only.
To learn more about queued operations, see the html documentation.
FILES
/etc/rsyslog.conf
Configuration file for rsyslogd
SEE ALSO
rsyslogd(8), logger(1), syslog(3)
The complete documentation can be found in the doc folder of the rsyslog distribution or online at
http://www.rsyslog.com/doc
Please note that the man page reflects only a subset of the configuration options. Be sure to read the html documentation for all features
and details. This is especially vital if you plan to set up a more-then-extremely-simple system.
AUTHORS
rsyslogd is taken from sysklogd sources, which have been heavily modified by Rainer Gerhards (rgerhards@adiscon.com) and others.
Version 7.2.0 22 October 2012 RSYSLOG.CONF(5)