File Permissions

On a Linux operating system, each file and directory is assigned access permissions for the owner of the file, the members of a group of related users and everybody else. This is to make sure that one user is not allowed to access the files and resources of another user.

Chmod command

The chmod command is used to modify files and directories permissions in Linux.

The chmod command accepts permissions in as a numerical argument. We can think of permission as a series of bits with 1 representing True or allowed and 0 representing False or not allowed.

Permission	rwx	Binary	Decimal
Read, write and execute	rwx	111	7
Read and write	rw-	110	6
Read and execute	r-x	101	5
Read only	r--	100	4
Write and execute	-wx	011	3
Write only	-w-	010	2
Execute only	--x	001	1
None	---	000	0

Each digit is independent of the other two. Therefore, 750 means the current user can read, write, and execute, the group cannot write, and others cannot read, write, or execute.

744, which is a typical default permission, allows read, write, and execute permissions for the owner, and read permissions for the group and “world” users.