Why DAR does save UID/GID instead of plain usernames and usergroups?

In each file property there is not present the name of the owner nor the name of the group owner, but instead are present two numbers, the user ID and the group ID (UID & GID in short). In the /etc/password file these numbers are associated names and other properties, like the login shell, the home directory, the password (see also /etc/shadow). Thus, when you do a directory list (with the 'ls' command for example or with any GUI program for another example), the listing application used does open each directory, there it finds a list of name and a inode number associated, then the listing program fetchs the inode attributes for each file and looks among other information for the UID and the GID.

To be able to display the real user name and group name, the listing application calls a given standard C library call that will do the lookup in /etc/password, eventually NIS system if configured and any other additional system, this way applications have not to bother with the many system ... more.

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