File Permissions in Linux

Linux operating system uses a permissions schema to define user rights for each file. These permissions establish:

-who can read the file. If the file is a directory, read means list the contents of the directory.
-who can write/modify the file. If the file is a directory, this permission defines if you can make any changes to the directory contents, for example create or delete files.
-who can execute the file. If the file is a directory, this permission defines if you can enter the directory and access its contents, for example run a search in the directory or execute a program in it.

Permissions are assigned to the file owner, to the file owner group, and to all users. For example, you can set a document to be readable and writable by the owner only, and just readable by everybody else.

When you issue an ls l command, to list all contents of a directory, you will see file permissions like this next to each file:

-rwxrwxrwx

This means this file can be read, written and executed by anybody. The first dash means this file is not a directory. For directories, there will be a d letter instead of a dash.

The first set of rwx...