Use lower case indexterms, and correct an egregious entry :

• <indexterm><primary>Configuring the <command>cron</command> utility</primary></indexterm>

+ <indexterm><primary>cron</primary>
+ <secondary>configuration</secondary></indexterm>

This is wrong for many many reasons :

• The indexterm is way too long and is a direct copy of the title of the section it resides in. The index is not a table of contents.
• Two columns of index terms should fit at the back of the printed book, so four words is almos always out of the question.
• indexterms relating to cron should appear near (as a subterm of) the 'cron' entry, not as a new 'Configuration blah' entry.