I am running through some system upgrades and my package manager is showing changes between the upstream /etc/shadow and mine.  I would like to put some comments in the file for next time this happens.  How would I accomplish putting comments in the /etc/shadow file without breaking things.I am thinking default # would likely do it, but if I get this wrong the reboot won't be that enjoyable.
How do I put comments in my /etc/shadow file?
password
On Linux systems using GNU libc, lines starting with # are ignored in /etc/shadow. The parsing is done by __fgetspent_r(), and its source code explicitly handles (and documents) this behaviour.So on the vast majority of Linux systems you can comment lines in /etc/shadow with # without causing problems.Unfortunately comments are dropped when /etc/shadow is updated, e.g. by passwd; so storing comments isn't actually safe (from the comments' point of view).This means you need to find somewhere else to store your comments: two good suggestions are dr01's idea of using /etc/shadow.README, or better yet Gilles' idea of using commit messages with etckeeper.