Chmod refers to change mode, a command for changing file access permissions in a UNIX-based operating system.
The chmod, or change mode, command allows an administrator to set or modify a file’s permissions. Every UNIX 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.
UNIX systems have many users. In this context, a user may refer to an individual or a system operation. UNIX identifies each user with a UID, and users may be organized into groups.
The syntax of the chmod command is:
chmod mode file
chmod 720 readme.txt
Each number in the mode parameter represents the permissions for a user or group of users:
Table 1 shows the eight numbers that can be used within the chmod parameter. The rwx column specifies read, write, and excecute 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 excecute.
|3||write and execute||011|
|5||read and execute||101|
|6||read and write||110|
|7||read, write, and excecute||111|
Table 1. chmod mode parameters.
For example, if you set your directory permissions to 720, then your permissions would function as follows:
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