Linux’s security model uses numbers to identify users and groups, but people prefer names. The names are stored, along with other important information, in two system databases.
When you type
ls -l to list the contents of the current directory, the third and fourth columns give the user ID and group ID that owns each file. It looks like this:
drwxrwxr-x 5 christid christid 1024 Aug 15 02:30 christid drwxr-xr-x 73 johnsonm root 4096 Jan 18 12:48 johnsonm drwxr-xr-x 25 kim root 2048 Jan 12 21:13 kim drwxrwsr-x 2 tytso tytso 1024 Jan 30 1996 tytso
But the kernel does not store the string
christid anywhere; the ls program is translating from kernel-supplied numbers to names. It ...