Checking for file integrity and tampering

In this section, we are going to learn how to check the integrity of a file and how to check for tampering by writing a simple shell script. Why do we need to check integrity? The answer is simple: administrators check integrity when there are passwords and libraries present on a server, as well as when files contain highly sensitive data.

Getting ready

Besides having a terminal open, you need to make sure the necessary files and directories are present.

How to do it...

1. We are going to write a script to check whether a file in a directory has been tampered with. Create an integrity_check.sh script and add the following code to it:

#!/bin/bash
E_DIR_NOMATCH=50
E_BAD_DBFILE=51
dbfile=Filerec.md5
# storing records.
set_up_database ()
{
    echo ""$directory"" > "$dbfile"
    # Write directory name to first line of file.
md5sum "$directory"/* >> "$dbfile"
    # Append md5 checksums and filenames.
}
check_database ()
{
    local n=0
    local filename...