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-com‐
patible 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 probably in a separate
package if you installed rsyslog via a packaging system. To use rsyslog's ad‐
vanced 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 mod‐
ules. 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 messages. Please
note that plain TCP syslog does NOT provide truly reliable delivery, with
it messages may be lost when there is a connection 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
$ModLoad imuxsock
in order to receive log messages from local system processes. This config
directive should only left out if you know exactly what you are doing.
BASIC STRUCTURE
Lines starting with a hash mark ('#') and empty lines are ignored. Rsyslog.conf
should contain following sections (sorted by recommended order in file):
Global directives
Global directives set some global properties of whole rsyslog daemon, for
example size of main message queue ($MainMessageQueueSize), loading ex‐
ternal 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 be‐
fore 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 man‐
page.
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 prior‐
ity, 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 lo‐
cal0 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 mes‐
sage.
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 follow‐
ing 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
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 priori‐
ties 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 extensions then 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" directive 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 dis‐
able 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 (fi‐
fos). 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 debug‐
ging. Note that the fifo must be created with the mkfifo(1) command before rsys‐
logd(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 transport 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 for‐
ward 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 proba‐
bly 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 "de‐
vice" option for the omfwd module.
Example:
action(type="omfwd" Target="192.168.0.1" Device="eth0" Port=514 Proto‐
col="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 setting 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 documentation.
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 ":omus‐
rmsg:" followed by the login name. You may specify more than one user by sepa‐
rating 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 Monitor‐
Ware-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 dis‐
carded. 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 fil‐
ters, 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. Out‐
put 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". Out‐
put channels support template definitions like all all other actions.
Shell execute
This executes a program in a subshell. The program is passed the template-gener‐
ated 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 ef‐
fective 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 of‐
fer the best performance for this job.
Property-Based Filters
Property-based filters are unique to rsyslogd. They allow to filter on any prop‐
erty, 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-sen‐
sitive, 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 prop‐
erty
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 prop‐
erty 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 mes‐
sages and so on. Templates compatible with the stock syslogd formats are hard‐
coded into rsyslogd. If no template is specified, we use one of these hardcoded
templates. Search for "template_" in syslogd.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:
$template MyTemplateName,"\7Text %property% some more text\n",<options>
The "$template" is the template directive. It tells rsyslog that this line con‐
tains a template. The backslash is an escape character. For example, \7 rings
the bell (this is an ASCII value), \n 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 contents of the syslog
message. Properties are accessed via the property replacer and it can for exam‐
ple pick a substring or do date-specific formatting. More on this is the PROP‐
ERTY REPLACER section of this manpage.
To escape:
% = \%
\ = \\ --> '\' is used to escape (as in C)
$template TraditionalFormat,"%timegenerated% %HOSTNAME% %syslogtag%%msg%\n"
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 dy‐
namic 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 character
by their backslash-escaped counterpart ("´" and "\") inside each
field. Please note that in MySQL configuration, the NO_BACK‐
SLASH_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 single
quotes ("'") by two single quotes ("''") inside each field. You
must use stdsql together with MySQL if in MySQL configuration 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 in‐
troduced their own escape methods, it is impossible to have a single option do‐
ing all the work. So you yourself must make sure you are using the right for‐
mat. 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%\n"
A template that tells you a little more about the message:
$template precise,"%syslogpriority%,%syslogfacility%,%timegener‐
ated%,%HOSTNAME%,
%syslogtag%,%msg%\n"
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%\n\r"
And a template with the traditional wall-message format:
$template wallmsg,"\r\n\7Message from syslogd@%HOSTNAME% at %timegener‐
ated%"
A template that can be used for writing to a database (please note the SQL tem‐
plate option)
$template MySQLInsert,"insert iut, message, receivedat values ('%iut%',
'%msg:::UPPERCASE%', '%timegenerated:::date-mysql%') into syste‐
mevents\r\n", SQL
NOTE 1: This template is embedded into core application under name Std‐
DBFmt , 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 fol‐
lows:
$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 ex‐
actly 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 prop‐
erties can be accessed and manipulated by the property replacer. With it, it is
easy to use only part of a property value or manipulate the value, e.g. by con‐
verting 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 necessarily 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-sys‐
log-protocol
APP-NAME
The contents of the APP-NAME field from IETF draft draft-ietf-syslog-pro‐
tocol
PROCID The contents of the PROCID field from IETF draft draft-ietf-syslog-proto‐
col
MSGID The contents of the MSGID field from IETF draft draft-ietf-syslog-proto‐
col
$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 po‐
sition-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 anything 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 reg‐
ular 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 ex‐
ample where the 3rd field (delimited by TAB) from the msg property is extracted
is as follows: "%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 up‐
per case works, lower case will return an error. There are no white spaces per‐
mitted inside the sequence (that will lead to error messages and will NOT pro‐
vide the intended result).
Property Options
Property options are case-insensitive. Currently, the following options are de‐
fined:
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 con‐
trol characters, escape sequences nor any other replacement character
like space.
QUEUED OPERATIONS
Rsyslogd supports queued operations to handle offline outputs (like remote sys‐
logd'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 distri‐
bution or online at
https://www.rsyslog.com/doc/
Please note that the man page reflects only a subset of the configuration op‐
tions. 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)