Devialog

Devialog is a simple anomaly based syslog analyzer written in Perl. The package consists of two Perl scripts:

• devialogsig  generator of Perl regular expression representing "known" messages signatures in the sample syslog file. Signatures are generated as Perl hash.
• devialog the anomaly detector.

The style of programming reminds top quality shell scripts style, not so much perverted complexity many Perl gurus adopt as the style.

There some architectural strong points

• generation of anomalies as Perl hash;
• When an anomaly is found devialog can execute arbitrary additional commands including scripts, mail the line as an alert, or simply write all anomalies to a file for periodical review.
• style of using hashes in the script,
• method of emulation of Switch in Perl-- the script was written before Perl 5.10 was available

Some weaknesses

• Christmas tree like options set, lack of discipline in inventing and handling options, some options probably unnecessary or redundant and just complicate codebase.
• Sub optional comparison of messages with database (linear not structured by daemon). That does not matter much as it process the tail of the /var/log/messages file not the whole file.
• Mail functionality can be implemented without Perl module Sendmail which is not standard in Perl installations on most Unixes

Codebase of devialog can be substantially simplified, probably cut in half

• Windows and Apache parts can be deleted, those parts are not fully functional anyway.
• Configuration can be processed by a separate script generating Perl file in the same style as anomaly database.
• Ability to watch multiple files can be eliminated.  It does not add much to the table as you can always create several separate invocations of the script.

Signature Creation

With an included utility, devialogsig, the initial "draft" signatures are created automatically and can edited as you get experience with the product.

• First signatures which represent important, "non-noise" lines should be deleted.
• Then some of the regular expression can be modified, for example generalized

Alert email contain generated signature so if the message represents noise it can be immediately added to the signature file.

The script operates on a single message basis. There is no ability to correlate sequences of syslog messages (like for example in case of reboot).

Signature additions are as simple as a cut and paste of regular expressions.
 

devialogsig

• -l Use this logfile to create anomaly signature file
• -c Output anomaly signatures to this file
• -C Show line count as you go
• -o Print one signature per line
• -p Print results as you go
• -r Read in previously created devialog signature base
• -D Debug mode
• -h This menu

devialog Quick Start Guide

1. As root, install the required Perl modules (if needed)

# perl -MCPAN -e 'install Mail::Sendmail'
# perl -MCPAN -e 'install File::Tail'
2. It is suggested to run devialog as a non-root user, self contained in the users home directory. Therefore, as root, add a user, give the user permissions to read the syslog files, create and set permissions on anomalies file and unzip the devialog-current.tgz tarball to the newly added home directory

# adduser devialog
# chown devialog /var/log/messages
# chmod 400 /var/log/messages
# touch /var/log/anomalies
# chown devialog /var/log/anomalies
# chmod 600 /var/log/anomalies
# su - devialog
$ tar xvfz /path/to/devialog-current.tgz
$ cd devialog-current/
3. If devialog is to be run on a central syslog repository, ensure syslog is presently running and configured to startup in listening mode with the "-r" switch. It is highly recommended to configure a host to be a central syslog repository if you intend on monitoring many systems.

   # syslogd -r
   

4. Open devialog.conf in your favorite editor. This file is well commented and contains nearly all configuration settings. Please go through the file in its entirety and change the email addresses, mail servers, etc.
5. Run devialogsig.pl - Copy the following for a standard Linux install. This will need to be run for each logfile to be monitored that is configured in devialog.conf. For example,

   ./devialogsig.pl -l /var/log/messages -c signatures.pl -t syslog -C

   * devialog needs at least a day (ideally a week) of syslog to truly generate a useful signature base.

6. Edit signatures.pl. Remove the signatures you want to be considered anomalies and have the action(s) defined in the devialog.conf AnomalyAction directive performed. For example, you may want to have all logins or useradd syslog events emailed to the address defined in devialog.conf. Simply remove the signature matching the login or useradd from the signature file (if the signature exists). The action(s) as configured in devialog.conf will then be taken, whether that is emailing, writing to a file, etc.. Note that signatures.pl is never executed; it contains a .pl extension for syntax hilighting purposes.

7. Run devialog.

   ./devialog.pl -c devialog.conf

8. Become root and configure the system to start devialog upon boot. Add the following line to /etc/rc.d/rc.local (or elsewhere depending on your OS)

su - devialog -c "/path/to/devialog.pl

Etc

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Last modified: March 12, 2019