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6) Users, Groups and Permissions

Any Linux user has a UID (User ID), and belongs to a group (with a GID). All files in the system include permission settings, which state: Who's file it is, Who can access it, What type of access any other can have, etc.

This is being done like that:

-rw-r--r--   1 root     root         2669 May  3  2001 /etc/inittab

fuuugggooo

The left (f) will show special setting of this file, for example, 'd' for directory.

The next 3 'u' will show the permissions the owner has on his file. Whether it’s to read, execute, or to write.

The next 3 'g' will show the permissions the group which the owner is part of (and it can be few groups, then all of them) will have on the file.

The last 3 'o' will show what permission has anyone who is not part of the two first symbols. This is called "Other".

In this case, we see that the file is also owned by root, who is the only one who can change it. Anyone else can only read it.

R is for read; W is for write and X is for execute.