As you know, every file in your Unix OS belongs to some user and some group. It is very easy to confirm the ownership of any file because user id and group id which own the file are always linked to the file. However, sometimes you can't tell which user owns the file, and today I'm going to explain why. It's a rather lengthy post and a complicated matter, so please leave questions or comments to help me polish this article off.
Files and directories ownership in Unix
If you look at any file using ls command, you will see an output like the one shown below – it reveals file access permissions, user and group id of the owner, the modification timestamp and the file name itself:
ubuntu$ ls -l /tmp/myfile -rw-r--r-- 1 greys admin 0 Jan 6 03:51 /tmp/myfile