20.7 Creating a Timestamp File for Selective Backups

Whenever I upgraded to a new version of UNIX, one common problem was making sure I maintained all of the changes made to the standard release of UNIX. Previously, I did an ls -lt (16.2) in each directory, and then I examined the modification date. The files that were changed have an obviously newer date than the original programs [unless the changed files come from a tar archive, with their original modification dates preserved! -JP ] Even so, finding every change was tedious, as there were dozens of directories to be searched.

A better solution is to create a file as the first step in upgrading. I usually call this FirstFile. find has a -newer option (17.8) that tests each file and compares the modification date to the newer file. If you then wanted to list all files in /usr that need to be saved when the operating system is upgraded, use:

% find /usr -newer /usr/FirstFile -print

This could then be used to create a tar (19.5) or cpio (19.9) file that would be restored after the upgrade.