From Gentoo Wiki
Jump to:navigation Jump to:search

This article has some todo items:
  • add simple IPv6 example
  • verify syntax
  • wikify
  • add systemd

Rsyslog is an open source system for high performance log processing. More than a regular system logger, it is a versatile tool that can take input from many sources and output to many destinations.

Rsyslog supports forwarding log messages over an IP network, to databases, email, etc. and extends the basic syslog protocol with powerful filtering capabilities. It provides powerful configuration options to adapt to specific needs.


USE flags

USE flags for app-admin/rsyslog An enhanced multi-threaded syslogd with database support and more

clickhouse Build the ClickHouse output module (requires net-misc/curl)
curl Enable http_request() function in RainerScript (requires net-misc/curl)
dbi Build the general database output module (requires dev-db/libdbi)
debug Enable extra debug codepaths, like asserts and extra output. If you want to get meaningful backtraces see
doc Add extra documentation (API, Javadoc, etc). It is recommended to enable per package instead of globally
elasticsearch Build the Elasticsearch output module (requires net-misc/curl)
gcrypt Add support for encrypted log files using dev-libs/libgcrypt
gnutls Build the GnuTLS network stream driver (requires net-libs/gnutls)
imhttp Build the http input module (requires www-servers/civetweb)
impcap Build the pcap input module (requires net-libs/libpcap)
jemalloc Use dev-libs/jemalloc for memory management
kafka Build the Apache Kafka input/output module (requires dev-libs/librdkafka)
kerberos Build the GSSAPI input and output module (requires virtual/krb5)
kubernetes Build the kubernetes modify plugin (requires net-misc/curl)
mdblookup Build the MaxMind DB lookup message modify plugin using dev-libs/libmaxminddb
mongodb Build the MongoDB output module (requires dev-libs/mongo-c-driver)
mysql Build the MySQL database output module (requires virtual/mysql)
normalize Build the normalize modify module (requires dev-libs/libee and dev-libs/liblognorm)
omhttp Build the http output module (requires net-misc/curl)
omhttpfs Build the httpfs output module (requires net-misc/curl)
omudpspoof Build the udpspoof output module (requires net-libs/libnet)
openssl Build the OpenSSL network stream driver (requires dev-libs/openssl)
postgres Build the PostgreSQL database output module (requires dev-db/postgresql)
rabbitmq Build the RabbitMQ output module (requires net-libs/rabbitmq-c)
redis Build the Redis output module using (requires dev-libs/hiredis)
relp Build the Reliable Event Logging Protocol (RELP) output module (requires dev-libs/librelp)
rfc3195 Build the rfc3195 input module (requires dev-libs/liblogging)
rfc5424hmac Build the rfc5424hmac modify module (requires dev-libs/openssl)
snmp Build the snmp modify and output module (requires net-analyzer/net-snmp)
ssl Add support for encrypted client/server communication (requires net-libs/gnutls)
systemd Build the journal input and output module (requires sys-apps/systemd)
test Enable dependencies and/or preparations necessary to run tests (usually controlled by FEATURES=test but can be toggled independently)
usertools Installs the user tools (rsgtutil, rscryutil...) corresponding to the set USE flags
uuid Include UUIDs in messages (requires sys-apps/util-linux)
xxhash Enable xxHash support in fmhash module (requires dev-libs/xxhash)
zeromq Build the ZeroMQ input and output modules (requires net-libs/czmq)


Install app-admin/rsyslog:

root #emerge --ask app-admin/rsyslog
It is a bad idea to run more than one system logger on a physical host. Other local loggers should be removed or disabled.




Add rsyslog to default run level:

root #rc-update add rsyslog default

After the emerge has finished, rsyslog should work out of the box with the default configuration; at least for local logging.

Start rsyslog by running:

root #rc-service rsyslog start

Check file /var/log/messages for syslog entries:

root #tail -f /var/log/messages
2024-01-30T23:24:27.462647+01:00 server rsyslogd: [origin software="rsyslogd" swVersion="8.2212.0" x-pid="2404" x-info=""] start


Basic rsyslog configuration:

FILE /etc/rsyslog.conf
$IncludeConfig /etc/rsyslog.d/
$FileCreateMode 0640

*.info;mail.none;authpriv.none;cron.none                -/var/log/messages
authpriv.*                                              /var/log/secure
mail.*                                                  -/var/log/maillog
cron.*                                                  -/var/log/cron
*.emerg                                                 .*

Typically messages are logged to files, the file has to be specified with full pathname. Rsyslog uses a simple syntax to filter incoming messages. Syslog messages are classified by facility and severity. According to RFC5424 following severity groups have been defined:


Numerical Code Severity Description
0 emerg system is unusable
1 alert action must be taken immediately
2 crit critical conditions
3 error error conditions
4 warning warning conditions
5 notice normal but significant condition
6 info informational messages
7 debug debug-level messages


List of facilities used by rsyslog. Most facilities names are self explanatory. Facilities local0 - local7 common usage is f.e. as network logs facilities for nodes and network equipment. Generally it depends on the situation how to classify logs and put them to facilities. See facilities more as a tool rather than a directive to follow.

Facilities can be adjusted to meet the needs of the user:

Numerical Code Facility Description
0 kern kernel messages
1 user user-level messages
2 mail mail system
3 daemon system daemons
4 auth security/authorization messages
5 syslog messages generated internally by syslogd
6 lpr line printer subsystem
7 news network news subsystem
8 uucp UUCP subsystem
9 cron clock daemon
10 security security/authorization messages
11 ftp FTP daemon
12 ntp NTP subsystem
13 logaudit log audit
14 logalert log alert
15 clock clock daemon (note 2)
16 local0 local use 0 (local0)
17 local1 local use 1 (local1)
18 local2 local use 2 (local2)
19 local3 local use 3 (local3)
20 local4 local use 4 (local4)
21 local5 local use 5 (local5)
22 local6 local use 6 (local6)
23 local7 local use 7 (local7)


List of filtering examples:

  • Redirect all incoming messages from all facilities and with all severeties to /var/log/syslog
 *.* -/var/log/syslog
  • Filter out messages with severity critical and save to file /var/log/critical
 *.crit -/var/log/critical
  • Do NOT redirect facilities mail, authentication and cron and mail to /var/log/messages, look for the keyword none
 mail.none;authpriv.none;cron.none -/var/log/messages

Local logging

Enable local logging from all facilities, to see local events at all.


Remote logging

To use remote logging to a syslog server, specify a client to log to a specific server or servers. And a server to receive messages sent by clients. Before configuring choose the protocol. Syslog messages can be sent using UDP or TCP. UDP is the default protocol and supported on most platforms. Not all platforms support TCP for syslog.


To enable syslog UDP messages sending add following line to the /etc/rsyslog.conf file. In this example rsyslog sends all facilities and all priorities *.* using protocol UDP @ to remote server

 *.*       @

To enable TCP support for syslog messages, put following line to the rsyslog configuraton file, TCP is enabled by adding @@.

 *.*       @@

If desired, hostnames can be substituted in for IP addresses.

Substitute with the IP address of the rsyslog server.

Below a example syslog client configuration to send syslog messages to a remote server via TCP.

FILE /etc/rsyslog.conf
*.*   @@

*.info;mail.none;authpriv.none;cron.none      /var/log/messages
authpriv.*                                    /var/log/secure
mail.*                                        /var/log/maillog
cron.*                                        /var/log/cron
*.emerg                                       *
uucp,news.crit                                /var/log/spooler
local7.*                                      /var/log/boot.log


To Provide UDP log reception and run the server on port 514. Running syslog with UDP is the default configuration.

 $ModLoad imudp
 $UDPServerRun 514

UDP is not a reliable protocol. For more reliability run the server with TCP logging support.

 $ModLoad imtcp
 $InputTCPServerRun 10514

To bind the UDP Port to an IP interface configure following entry, ensure the right sequence of definitions if binding to an interface:

 $ModLoad imudp
 $UDPServerAddress # this entry MUST be before the $UDPServerRun directive
 $UDPServerRun 514

A simple configuration would look like this one:

FILE /etc/rsyslog.conf
$InputTCPServerRun 10514
$UDPServerRun 514
*.info;mail.none;authpriv.none;cron.none      /var/log/messages
authpriv.*                                    /var/log/secure
mail.*                                        /var/log/maillog
cron.*                                        /var/log/cron
*.emerg                                       *
uucp,news.crit                                /var/log/spooler
local7.*                                      /var/log/boot.log

Database logging

Rsyslog supports logging to following databases:

After choosing the database logs will be stored to a proper USE flag needs to be enabled and rsyslog has to be rebuild before continuing. This example uses a MySQL database.

Next steps assume a working MySQL database server running on localhost, for installation details follow the MySQL article.

The package ships a SQL script named createDB.sql to create the database layout.

FILE /usr/share/rsyslog/scripts/mysql/createDB.sql
USE Syslog;
        ID int unsigned not null auto_increment primary key,
        CustomerID bigint,
        ReceivedAt datetime NULL,
        DeviceReportedTime datetime NULL,
        Facility smallint NULL,
        Priority smallint NULL,
        FromHost varchar(60) NULL,
        Message text,
        NTSeverity int NULL,
        Importance int NULL,
        EventSource varchar(60),
        EventUser varchar(60) NULL,
        EventCategory int NULL,
        EventID int NULL,
        EventBinaryData text NULL,
        MaxAvailable int NULL,
        CurrUsage int NULL,
        MinUsage int NULL,
        MaxUsage int NULL,
        InfoUnitID int NULL ,
        SysLogTag varchar(60),
        EventLogType varchar(60),
        GenericFileName VarChar(60),
        SystemID int NULL
CREATE TABLE SystemEventsProperties
        ID int unsigned not null auto_increment primary key,
        SystemEventID int NULL ,
        ParamName varchar(255) NULL ,
        ParamValue text NULL

Import the /usr/share/rsyslog/scripts/mysql/createDB.sql file to create the Syslog database.

user $mysql -u root -p < /usr/share/rsyslog/scripts/mysql/createDB.sql

Create a datebase user for the Syslog database:

mysql>GRANT ALL ON Syslog.* TO rsyslog-user@localhost IDENTIFIED BY - 'MySecretPassword';

To provide SQL database logging support, enable the needed module in /etc/rsyslog.conf


Tell rsyslog to forward all data to the database, add following to the end of the /etc/rsyslog.conf file:

 *.* :ommysql:localhost,Syslog,rsyslog-user,MySecretPassword

Finally Restart the rsyslog server to adapt new settings

root #/etc/init.d/rsyslog restart


Many vendors format their syslog messages differently. If the network equipment logs to a central rsyslog server the difference in logging will be easy to notice. After some time of log dumping it will be difficult to filter the syslog server messages for a certain

  • Date
  • Facility
  • Severity
  • Host
  • Syslogtag
  • ProcessID
  • MessageType
  • Message

To unify syslog messages to a certain or preferred format, Rsyslog uses templates which parse arriving messages and "rewrites" them to the desired format.

To maintain a simple and modular configuration, templates are stored within the /etc/rsyslog.d/ directory. To include files stored within the rsyslog.d directory add following line to /etc/rsyslog.conf file:

 $IncludeConfig /etc/rsyslog.d/*.conf

Templates should be stored to the /etc/rsyslog.d/ directory.

root #cd /etc/rsyslog.d/
Following templates are working very good, but are not perfect.

Here a simple template for a cisco IOS host which logs to rsyslogd:

FILE /etc/rsyslog.d/template_cisco.conf
$template mysql_cisco, "insert into SystemEvents (Message, Facility, FromHost, Priority, DeviceReportedTime, ReceivedAt, InfoUnitID, SysLogTag) values ('%msg:R,ERE,1,DFLT:%[A-Z0-9_-]+: (.*)--end%', %syslogfacility%, '%fromhost%', %syslog
priority%, '%timereported:::date-mysql%', '%timegenerated:::date-mysql%', %iut%, '%msg:R,ERE,0,DFLT:%[A-Z0-9_-]+:--end%')",SQL

Here a simple template for a ScreenOS host which logs to rsyslogd:

FILE /etc/rsyslog.d/template_netscreen.conf
$template mysql_netscreen, "insert into SystemEvents (Message, Facility, FromHost, Priority, DeviceReportedTime, ReceivedAt, InfoUnitID, SysLogTag) values ('%msg:R,ERE,1,DFLT:[a-zA-Z0-9-]+: (.*)--end%', %syslogfacility%, '%fromhost%', %s
yslogpriority%, '%timereported:::date-mysql%', '%timegenerated:::date-mysql%', %iut%, '%msg:R,ERE,0,DFLT:[a-zA-Z0-9-]+:--end%')",SQL

Here a simple template for Linux host which logs to rsyslogd:

FILE /etc/rsyslog.d/template_linux.conf
$template mysql_linux, "insert into SystemEvents (Message, Facility, FromHost, Priority, DeviceReportedTime, ReceivedAt, IntoUnitID, SysLogTag) values ('%msg%', %syslogfacility%, '%HOSTNAME%', %syslogpriority%, '%timereported:::
date-mysql%', '%timegenerated:::date-mysql%', %iut%, '%syslogtag:R,ERE,1,FIELD:(.+)(\[[0-9]{1,5}\]).*--end%')" ,SQL

Configure rsyslogd which predefined template to apply to which facility, add following template references to the end of the /etc/rsyslog.conf file:

  • All messages arriving at facility local4, are Cisco IOS messages:
 local4.* :ommysql:localhost,Syslog,rsyslog-user,MySecretPassword;mysql_cisco
  • All messages arriving at facility local5 , are ScreenOS messages:
 local5.* :ommysql:localhost,Syslog,rsyslog-user,MySecretPassword;mysql_netscreen
  • All messages arriving at syslog consider as Linux messages, and ignore local4 and local5 facilities which have their own templates.
 *.*;local4.none;local5.none :ommysql:localhost,Syslog,rsyslog-user,MySecretPassword;mysql_linux

The following is an example of how the /etc/rsyslog.conf file could look on a syslog server with working templates:

FILE /etc/rsyslog.conf
$ModLoad imudp
$UDPServerRun 514
$IncludeConfig /etc/rsyslog.d/*.conf

*.info;mail.none;authpriv.none;cron.none	-/var/log/messages
authpriv.*					/var/log/secure
mail.*						-/var/log/maillog
cron.*						-/var/log/cron
*.emerg						*
uucp,news.crit					-/var/log/spooler
local7.*					/var/log/boot.log

local4.* :ommysql:localhost,Syslog,rsyslog-user,MySecretPassword;mysql_cisco
local5.* :ommysql:localhost,Syslog,rsyslog-user,MySecretPassword;mysql_netscreen
*.*;local4.none;local5.none :ommysql:localhost,Syslog,rsyslog-user,MySecretPassword;mysql_linux

Reload rsyslog server to apply new changes:

root #/etc/init.d/rsyslog reload

Further examples can be found here.


Check if a syslog process is running :

root #ps ux | grep rsyslog
root     9161  0.0  0.0 1323652  3424 ?        Sl   00:51   0:00 /usr/sbin/rsyslogd -c5 -i /var/run/ -f /etc/rsyslog.conf

Verify network configuration:

root #ss -tulpn | grep rsyslog
udp   UNCONN 0      0  *    users:(("rsyslogd",pid=1710,fd=6))
udp   UNCONN 0      0  *    users:(("rsyslogd",pid=1710,fd=4))
udp   UNCONN 0      0               [::]:514          [::]:*    users:(("rsyslogd",pid=1710,fd=7))
udp   UNCONN 0      0               [::]:514          [::]:*    users:(("rsyslogd",pid=1710,fd=5))

Verify with the command logger, if messages are arriving in at the syslogserver:

user $logger -t test my syslog-test-message

Following message should appear in the /var/log/messages file if rsyslog is working properly:

root #tail /var/log/messages
2011-11-23T00:47:05+01:00 Rsyslogserver test: my syslog-test-message

See also

  • Metalog — an alternative syslog daemon.
  • Sysklogd — utility that reads and logs messages to the system console, logs files, other machines and/or users as specified by its configuration file.
  • Syslog-ng — a powerful, highly configurable monitoring and logging daemon.

External resources