How do you find out that somebody has accessed your system and changed your configuration or security settings? How do you verify file content? There is no simple answer to these questions. Personally, I use specialized tool such as tripwire and combination of perl / shell script, UNIX command line utilities.
Examine methods of storing and later checking the validity of your configuration files is one of the key task. This article provides some guideline. You will develop a script that you can use to generate information that checks the validity of a file or directory full of files. The recorded information includes the file path, a checksum of the file so that you can compare the file contents, and unique information about the file (inode, permissions, ownership information) so that you can identify differences should they occur:
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The typical UNIX administrator has a key range of utilities, tricks, and systems he or she uses regularly to aid in the process of administration. There are key utilities, command-line chains, and scripts that are used to simplify different processes. Some of these tools come with the operating system, but a majority of the tricks come through years of experience and a desire to ease the system administrator's life. The focus of this series is on getting the most from the available tools across a range of different UNIX environments, including methods of simplifying administration in a heterogeneous environment.