How to configure syslog server or a centralized log server in redhat linux rhel5 or centos

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This article will explain installing and configuring a syslog log server in redhat enterprise linux. It'll work in other redhat distributions like centos, fedora etc.

Centralized log server (syslog server)

Suppose we have a server and 5 client machines. And we want to monitor the logs of all those client machines. In situations like this, we will use centralized server as a log server. Whatever events are happening in client machines, the logs will be sent to the server. So that we can monitor all the logs from a centralized server. We make use of syslog service for this. You can also check out another log server like syslog-ng

Features of syslog:
1. Logs the daemon information to localhost
2. Logs the daemon information to Remote host
3. Logs the daemon information to List of users
4. Logs the daemon information to console


Instaltion Package is sysklogd
[root@apache ~]# rpm -q sysklogd
sysklogd-1.4.1-44.el5
[root@apache ~]#

Or you can check as follows:
[root@apache ~]# rpm -qf /etc/syslog.conf
sysklogd-1.4.1-44.el5
[root@apache ~]#

Starting the syslog daemon
[root@apache ~]# /etc/init.d/syslog start
Starting system logger:                                    [  OK  ]
Starting kernel logger:                                    [  OK  ]
[root@apache ~]#

Checking the process name. it is syslogd
[root@apache ~]# ps -ax | grep syslog
Warning: bad syntax, perhaps a bogus '-'? See /usr/share/doc/procps-3.2.7/FAQ
 5190 ?        Ss     0:00 syslogd -m 0
 5210 pts/0    S+     0:00 grep syslog
[root@apache ~]#

Configuration of server machine(syslog server)

Service name: syslog

configuration file: /etc/sysconfig/syslog

Steps:

1. Open the /etc/sysconfig/syslog file and add "-r" option to the variable SYSLOGD_OPTIONS as shown below.

[root@server ~]# cat /etc/sysconfig/syslog

# Options to syslogd

# -m 0 disables 'MARK' messages.

# -r enables logging from remote machines

# -x disables DNS lookups on messages recieved with -r

# See syslogd(8) for more details

SYSLOGD_OPTIONS="-r -m 0"

# Options to klogd

# -2 prints all kernel oops messages twice; once for klogd to decode, and

# once for processing with 'ksymoops'

# -x disables all klogd processing of oops messages entirely

# See klogd(8) for more details

KLOGD_OPTIONS="-x"

#

SYSLOG_UMASK=077

# set this to a umask value to use for all log files as in umask(1).

# By default, all permissions are removed for "group" and "other".

[root@server ~]#

2. Restart the syslog service.

[root@server ~]# service syslog restart

Shutting down kernel logger: [ OK ]

Shutting down system logger: [ OK ]

Starting system logger: [ OK ]

Starting kernel logger: [ OK ]

[root@server ~]#

Configuration for client machines

service name: syslog

Configuration file: /etc/syslog.conf

The configuration file /etc/syslog.conf has two parts
Eg:
*.info;mail.none;authpriv.none;cron.none                /var/log/messages
[selector field(Facility.priority)]      [action field]

They are selector field and actions field. Selector field is again divided into two. Facilities and priorities.
Facility examples are (authpriv,kern,mail,local7 etc)
The priority is one of the following in ascending order: debug(0), info, notice, warning(warn), error(err), crit, alert, emerg(panic(7))
Actions can be regular files, console, list of users, remote machine ip etc.

Steps:

1. Open the configuration file /etc/syslog.conf and add an entry to redirect the logs to the remote server.

[root@vm1 ~]# cat /etc/syslog.conf

# Log all kernel messages to the console.

# Logging much else clutters up the screen.

#kern.* /dev/console

*.* @192.168.0.19

# Log anything (except mail) of level info or higher.

# Don't log private authentication messages!

*.info;mail.none;authpriv.none;cron.none /var/log/messages

# The authpriv file has restricted access.

##authpriv.* /var/log/secure

# Log all the mail messages in one place.

mail.* -/var/log/maillog

# Log cron stuff

cron.* /var/log/cron

# Everybody gets emergency messages

*.emerg *

# Save news errors of level crit and higher in a special file.

uucp,news.crit /var/log/spooler

# Save boot messages also to boot.log

local7.* /var/log/boot.log

[root@vm1 ~]#

2. Restart the service

[root@vm1 ~]# service syslog restart

Shutting down kernel logger: [ OK ]

Shutting down system logger: [ OK ]

Starting system logger: [ OK ]

Starting kernel logger: [ OK ]

[root@vm1 ~]#

Checking:

In server open a terminal and watch /var/log/messages and restart syslog service in client. You can see the log from clinet coming to server.

[root@server ~]# tail -f /var/log/messages

Oct 15 14:42:30 vm1 kernel: Kernel logging (proc) stopped.

Oct 15 14:42:30 vm1 kernel: Kernel log daemon terminating.

Oct 15 14:42:31 vm1 exiting on signal 15

Oct 15 14:42:31 vm1 syslogd 1.4.1: restart.

Oct 15 14:42:31 vm1 kernel: klogd 1.4.1, log source = /proc/kmsg started.

Fields in log from remote machine:

Date Hostname Name_of_the_application: Actual_log_message

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Recommended Reading

1. Logging and Log Management: The Authoritative Guide to Dealing with Syslog, Audit Logs, Events, Alerts and other IT 'Noise'
2. Security Monitoring: Proven Methods for Incident Detection on Enterprise Networks
3. SYSLOG I
4. Linux Bible 
5. The Linux Command Line: A Complete Introduction
6. Amazon Web Services For Dummies 

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