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Change Mode (chmod) Meaning: What is chmod?

September 10, 2019

What is chmod? In UNIX/Linux-based operating systems, chmod refers to change mode, a command for changing file access permissions.

Change Mode (chmod) Meaning & Purpose

The chmod, or change mode, command allows an administrator to set or modify a file’s permissions. Every UNIX/Linux file has an owner user and an owner group attached to it, and every file has permissions associated with it. The permissions are as follows: read, write, or execute.

Change Mode (chmod) Meaning & Application

UNIX/Linux systems have many users. In this context, a user may refer to an individual or a system operation. UNIX/Linux identifies each user with a UID, and users may be organized into groups.

Change Mode (chmod) Syntax & Mode Parameters

The syntax of the chmod command is:

chmod mode file

Example:

chmod 720 readme.txt

Each number in the mode parameter represents the permissions for a user or group of users:

  • The first number represents the file’s owner.
  • The second number represents the file’s group.
  • The third number represents everyone else.

The Change Mode (chmod) Meaning & Mode Parameters Reference Table below shows the eight numbers that can be used within the chmod parameter. The rwx column specifies read, write, and execute access, offering a binary value for each operation. A "1" means "yes," a "0" means "no." If rwx reads 110, then that permission may read and write, but not execute.

Change Mode (chmod) Meaning & Mode Parameters Reference Table

#Permissionrwx
0none000
1execute only001
2write only010
3write and execute011
4read only100
5read and execute101
6read and write110
7 read, write, and execute 111

For example, if you set your directory permissions to 720, then your permissions would function as follows:

  • The file’s owner may read, write, and execute the file.
  • The file’s group may only write the file.
  • All others cannot access the file.

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Paul Stubblefield
Paul Stubblefield


Nexcess Knowledge Base Owner
Content Marketing in Nexcess Digital Marketing
Nexcess, A Liquid Web Brand

Paul Stubblefield
— Technical Writer & Knowledge Management Professional

"Delivering the next generation of life-enhancing technology platforms, software solutions, and mobile-ready applications for technology pioneers, thought leaders, and market innovators in a robustly connected world."

Paul lives in Bonita Springs, Florida, USA. He is an aficionado of art, coffee, good-natured humor, lifelong learning, music, nature, pets, technology, world cultures, and his Zen Patio Garden project.