Unable to log in to a user account

[Dennis Handly]

>why these permissions changed and how to prevent it to reoccur?

(You didn't change permissions, just ownership.)

Are you using NIS?  This could happen if something goes wrong with the NIS server.

Or the permissions on /etc/passwd aren't readable by everyone.

[Yaroki]

No, I am not using NIS. But It might concern to removing users'  accounts without deleting its home directories.

Then, something with their ownership file pass randomly to other existing user as a number.

But I don't know it for sure and furthermore, how to handle it...

[Dennis Handly]

>But It might concern to removing users'  accounts

Yes, if you delete user accounts, there no longer is a passwd entry to translate the UID into a name.

[Yaroki]

So, it inherited numbers instead?

What should I do now in order to overcome the problem? (it happens from time to time).

[Dennis Handly]

No, files always have numbers.  They just don't get translated to readable names.

>What should I do now in order to overcome the problem?

If you delete a user, you need to change ownership of all of the files owned by that user.

(Or you just "*" out that user passwd entry and keep it around.)