Linux Tutorials: Chmod Commands

In Unix and Unix-like operating systems, chmod is the command and system call used to change the access permissions and the special mode flags of file system objects. Collectively these were originally called its modes, and the name chmod was chosen as an abbreviation of change mode

1. Add single permission to a file/directory

Changing permission to a single set. + symbol means adding permission. For example, do the following to give execute permission for the user irrespective of anything else:

$ chmod u+x filename

2. Add multiple permission to a file/directory

Use comma to separate the multiple permission sets as shown below.

$ chmod u+r,g+x filename

3. Remove permission from a file/directory

Following example removes read and write permission for the user.

$ chmod u-rx filename

4. Change permission for all roles on a file/directory

Following example assigns execute privilege to user, group and others (basically anybody can execute this file).

$ chmod a+x filename

5. Make permission for a file same as another file (using reference)

If you want to change a file permission same as another file, use the reference option as shown below. In this example, file2’s permission will be set exactly same as file1’s permission.

$ chmod --reference=file1 file2

6. Apply the permission to all the files under a directory recursively

Use option -R to change the permission recursively as shown below.

$ chmod -R 755 directory-name/

7. Change execute permission only on the directories (files are not affected)

On a particular directory if you have multiple sub-directories and files, the following command will assign execute permission only to all the sub-directories in the current directory (not the files in the current directory).

$ chmod u+X *

Rajesh Kumar

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