If your system gzips and rotates your logs.

You can use this trick to search thru all of them.

# zgrep -i — “SEARCHTERM” $(ls -1Str /var/log/messages*)

Another way

# zgrep -i — . $(ls -1Str /var/log/messages*) | grep “SEARCHTERM”

Sidenote: if you get an error try to replace “zgrep” with “zegrep”