November 2004
Intermediate to advanced
736 pages
14h 4m
English
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 ...