RHEL6: Using Advanced Log File Filtering in Rsyslog

100-8591So by default when you forward logs to a syslog/rsyslog server all the logs end up in the same file (ususally configured to go to the messages file). Sometimes one may prefer to forward logs from a particular server to a separate logfile. I know for a fact that my sometimes friends in our info-sec group prefers this setup.

While managing such a setup for more than a handful of hosts would probably be a nightmare, its not actaually hard to setup on the most basic level.

First create a custom filters.conf (or whatever you want to name it) in your /etc/rsyslog.d directory. Below is the file that I created.

[root@ip-172-31-21-28 rsyslog.d]# cat filters.conf
:fromhost, isequal, "ip-172-31-25-104.ec2.internal" /var/log/ip-172-31-25-104.ec2.internal/messages
:fromhost, isequal, "ip-172-31-25-104.ec2.internal" ~

Note that you will need to include two lines in your file for each host, one with the specific file/location that you want to send your filtered log messages, and a second line that directs rsyslog to discard any messages from the specified hosts once they have been logged to the specified locations. This keeps these messages from ending up in the messages file as well as the file defined in your filter file.


Related articles

RHEL6 – Introduction to IPtables, Part II
HomeLab: Basic Syslog Configuration on Cisco Catalyst Devices
RHEL6- Getting Up Close and Personal With Rsyslog

HomeLab: Basic Syslog Configuration on Cisco Catalyst Devices

FrontiervilleblueoxIn my homelab setup I am dumping syslog on all my devices to my Linux desktop. Have not figure out what I am going to do with it yet, but I see myself either setting up Splunk or Greylog in the near future. Note, a while back I wrote a post on how to configure rsyslog on RHEL 6 – s0 if you are interested you can find that post here.

So lets get down to brass tacks and configure some freaking syslog.

In this instance we are configuring syslog redirection on a Cisco 3548xl switch. Note we are in configure terminal mode.

First we must tell our device to insert timestamps on

s-3550-1(config)#service timestamps log datetime

Now we tell the device where to send the syslog messages


Now we tell the device which log levels to send to the syslog server. In this instance I am sending warning level messages and above. This is pretty verbose, but its a home lab so I am not worried about a slew of log messages pounding my syslog server.

s-3550-1(config)#logging trap warning

For reference I am including the logging levels below.

Emergency: 0

Alert: 1

Critical: 2

Error: 3

Warning: 4

Notice: 5

Informational: 6

Debug: 7

Now lets review what we have done with the show logging command

s-3550-1#show logging
Syslog logging: enabled (0 messages dropped, 0 flushes, 0 overruns)
    Console logging: level debugging, 13 messages logged
    Monitor logging: level debugging, 0 messages logged
    Buffer logging: level debugging, 13 messages logged
    File logging: disabled
    Trap logging: level warnings, 13 message lines logged
        Logging to, 0 message lines logged


Note that this procedure is exactly the same on my Cisco 2621 switch.


Related articles

HomeLab: The Cisco 3560G
HomeLab: Simple SSH Setup on a Cisco Router
HomeLab: Cisco 3550 Switch Software Configuration Guide
Using Good Old Syslog When Troubleshooting (by Tony Fortunato)
HomeLab: Configuring the NTP Client on a Cisco Catalyst Switches
[PATCH 1/9] syslog_ns: add syslog_namespace and put/get_syslog_ns

RHEL6 – Getting Up Close and Personal With Rsyslog

LogRsyslog has replaced Syslog as the default logging daemon in RHEL6. Rsyslog was designed to complete with syslog-ng and has several enhancements over plain old syslog. This includes but is not limited to more granularity with timestamps, direct database logging,   TCP support, and  relay server names in host fields which makes it easier to track the path a message has taken.

Below we are going to take a look at a few simple rsyslog configuration items.

Configure Rsyslog to Accept Remote Logs.

Within /etc/rsyslog.conf, comment out either the TCP or UDP syslog reception lines below. TCP is more reliable, however UDP is more widely supported.

# Provides UDP syslog reception
#$ModLoad imudp.so
#$UDPServerRun 514

# Provides TCP syslog reception
#$ModLoad imtcp.so
#$InputTCPServerRun 514

Configure a Server to Send Logs to a Remote Host.

To send all messages of info priority or higher to a remote host via udp, use the following format. Note that is the remote server that I want to send logs to.

*.info    @

To send the same priorities to the remote host via TCP, use two "@@"

*.info    @@

Note that you can specify the port number on which to send by using IP:PORT. When no port is specified the default port of 514 is used.

Note that depending on your configuration you may need to alter your IPtables configuration on your sending and/or receiving server. In my case I needed to allow UDP on port 514 on my remote syslog server. To accomplish this I used system-config-firewall-tui which added the following line to /etc/sysconfig/iptables.

-A INPUT -m state –state NEW -m udp -p udp –dport 514 -j ACCEPT

Which shows up as what you see below in the output of 'iptables -L'

ACCEPT     udp  –  anywhere             anywhere            state NEW udp dpt:syslog

Testing Your Configuration

Ok lets send a test to our remote syslog server. Note that rsyslog has been restarted on both hosts.

# logger "testing to remote rsyslog server"

Checking the messages file on the remote host we can see that the test message has arrived.

Aug 13 14:55:26 vfatmin02 root: testing to remote rsyslog server