chmod Command in Linux with Examples

chmod Command

chmod command means change mode. There are three basic modes to files and directories: read, write, and execute. Additionally, each of these modes can be applied to the user, the group, or others.

Representations used for Ownerships

u - User
g - Group
o - Others

Representations used for File permission

r &ndash Read (value is 4)
w &ndash Write (value is 2)
x &ndash Execute (value is 1)

7 = 4+2+1 (read+write+execute)
6 = 4+2 (read+write)
5 = 4+1 (read+execute)
4 = 4 (read)
3 = 2+1 (write+execute)
2 = 2 (write)
1 = 1 (execute)

Syntax

chmod [OPTION]... MODE[,MODE]... FILE...
chmod [OPTION]... OCTAL-MODE FILE...
chmod [OPTION]... --reference=RFILE FILE...

Applying single permission to a file/directory

We are going to add the executable permission for the user using chmod command.

Example
First let we list the files present in the current directory.

[user1@linuxhelp Desktop]$ ll 
total 12
drwxrwxr-x 2 user1 user1 4096 Feb 25 14:45 dir1
-rw-rw-r-- 1 user1 user1   21 Feb 25 14:45 file1
-rw-rw-r-- 1 user1 user1   29 Feb 25 14:46 file2
[user1@linuxhelp Desktop]$ chmod o+w file2 
[user1@linuxhelp Desktop]$ ll 
total 12
drwxrwxr-x 2 user1 user1 4096 Feb 25 14:45 dir1
-rw-rw-r-- 1 user1 user1   21 Feb 25 14:45 file1
-rw-rw-rw- 1 user1 user1   29 Feb 25 14:46 file2

You can see the others permission of the file has been changed from r to rw

Applying multiple permissions for different ownership in a single command

We are going to change the file permission of the user & group in single commands using chmod command.

Example

[user1@linuxhelp Desktop]$ ll 
total 12
drwxrwxr-x 2 user1 user1 4096 Feb 25 14:45 dir1
-rw-rw-r-- 1 user1 user1   21 Feb 25 14:45 file1
-rw-r--r-- 1 user1 user1   29 Feb 25 14:46 file2
[user1@linuxhelp Desktop]$ chmod u+x,g+x file1 
[user1@linuxhelp Desktop]$ ll 
total 12
drwxrwxr-x 2 user1 user1 4096 Feb 25 14:45 dir1
-rwxrwxr-- 1 user1 user1   21 Feb 25 14:45 file1
-rw-r--r-- 1 user1 user1   29 Feb 25 14:46 file2

Now in the above output, the file permission of the user and the group has been changed.

Removal of permission for both file and directory in a single command

Using this chmod command we can modify the permissions of a file and a directory in a single command

Example

[user1@linuxhelp Desktop]$ ll 
total 12
drwxrwxr-x 2 user1 user1 4096 Feb 25 14:45 dir1
-rwxrwxr-- 1 user1 user1   21 Feb 25 14:45 file1
-rw-r--r-- 1 user1 user1   29 Feb 25 14:46 file2
[user1@linuxhelp Desktop]$ chmod u-x,g-x file1 dir1/ 
[user1@linuxhelp Desktop]$ ll 
total 12    
drw-rw-r-x 2 user1 user1 4096 Feb 25 14:45 dir1
-rw-rw-r-- 1 user1 user1   21 Feb 25 14:45 file1
-rw-r--r-- 1 user1 user1   29 Feb 25 14:46 file2

Now the file permissions of the user and group is removed from rwx to rw

Removal of permission for file/directory

Here we are just removing the multiple permissions of a single file using chmod command.

Example

[user1@linuxhelp Desktop]$ ll 
total 12
drwxrwxr-x 2 user1 user1 4096 Feb 25 14:45 dir1
-rwxrwxr-- 1 user1 user1   21 Feb 25 14:45 file1
-rw-r--r-- 1 user1 user1   29 Feb 25 14:46 file2
[user1@linuxhelp Desktop]$ chmod u-x,g-x file1 
[user1@linuxhelp Desktop]$ ll 
total 12
drwxrwxr-x 2 user1 user1 4096 Feb 25 14:45 dir1
-rw-rw-r-- 1 user1 user1   21 Feb 25 14:45 file1
-rw-r--r-- 1 user1 user1   29 Feb 25 14:46 file2

Removal of permissions of all roles of ownership of a file

Using this chmod command we can remove same permissions of all ownerships.

Example

[user1@linuxhelp Desktop]$ ll 
total 12
drwxrwxr-x 2 user1 user1 4096 Feb 25 14:45 dir1
-rw-rw-r-- 1 user1 user1   21 Feb 25 14:45 file1
-rw-r--r-- 1 user1 user1   29 Feb 25 14:46 file2
[user1@linuxhelp Desktop]$ chmod a-r * 
[user1@linuxhelp Desktop]$ ll 
total 12
d-wx-wx--x 2 user1 user1 4096 Feb 25 14:45 dir1
--w--w---- 1 user1 user1   21 Feb 25 14:45 file1
--w------- 1 user1 user1   29 Feb 25 14:46 file2

Applying execute permissions only to all directories without making changes in file

The following chmod command make changes only in all directories present inside the target directory and not on files present inside it.

Example

[user1@linuxhelp Desktop]$ ll 
total 12
drwxrwxr-x 2 user1 user1 4096 Feb 25 14:45 dir1
-rw-rw-r-- 1 user1 user1   21 Feb 25 14:45 file1
-rw-r--r-- 1 user1 user1   29 Feb 25 14:46 file2
[user1@linuxhelp Desktop]$ chmod a+X * 
[user1@linuxhelp Desktop]$ ll 
total 12
drwxrwxr-x 2 user1 user1 4096 Feb 25 14:45 dir1
-rw-rw-r-- 1 user1 user1   21 Feb 25 14:45 file1
-rw-r--r-- 1 user1 user1   29 Feb 25 14:46 file2

Applying permission for a file from same as another reference file

Now we are going to change the file permission of a file as another file by using reference option

Example

[user1@linuxhelp Desktop]$ ll 
total 12
drwxrwxr-x 2 user1 user1 4096 Feb 25 14:45 dir1
-rwxrwxrwx 1 user1 user1   21 Feb 25 14:45 file1
-rw-r--r-- 1 user1 user1   29 Feb 25 14:46 file2
[user1@linuxhelp Desktop]$ chmod --reference=file1 file2 
[user1@linuxhelp Desktop]$ ll 
total 12
drwxrwxr-x 2 user1 user1 4096 Feb 25 14:45 dir1
-rwxrwxrwx 1 user1 user1   21 Feb 25 14:45 file1
-rwxrwxrwx 1 user1 user1   29 Feb 25 14:46 file2

In the above output the file permission the file ' sample' is assigned to the file ' example'

Change permission for all ownership on a file/directory

This command is about how to change the permission all role (user, group and others)

Example

[user1@linuxhelp Desktop]$ ll 
total 12
drwxrwxr-x 2 user1 user1 4096 Feb 25 14:45 dir1
-rw-r--r-- 1 user1 user1   21 Feb 25 14:45 file1
-rw-r--r-- 1 user1 user1   29 Feb 25 14:46 file2
[user1@linuxhelp Desktop]$ chmod a+rwx file1 
[user1@linuxhelp Desktop]$ ll 
total 12
drwxrwxr-x 2 user1 user1 4096 Feb 25 14:45 dir1
-rwxrwxrwx 1 user1 user1   21 Feb 25 14:45 file1
-rw-r--r-- 1 user1 user1   29 Feb 25 14:46 file2

Apply the permission to all the files under a directory recursively

Now we are going to change the file permission of a directory recursively that is the given file permission is applied to the mentioned directory and their sub-directories.

Example

[user1@linuxhelp Desktop]$ ll 
total 12
drwxr-xr-x 5 user1 user1 4096 Feb 25 15:29 dir1
-rwxrwxrwx 1 user1 user1   21 Feb 25 14:45 file1
-rw-r--r-- 1 user1 user1   29 Feb 25 14:46 file2
[user1@linuxhelp Desktop]$ chmod -R o+w dir1/ 
[user1@linuxhelp Desktop]$ ll 
total 12
drwxr-xrwx 5 user1 user1 4096 Feb 25 15:29 dir1
-rwxrwxrwx 1 user1 user1   21 Feb 25 14:45 file1
-rw-r--r-- 1 user1 user1   29 Feb 25 14:46 file2
[user1@linuxhelp Desktop]$ cd dir1/ 
[user1@linuxhelp dir1]$ ll 
total 12
drwxr-xrwx 2 user1 user1 4096 Feb 25 15:29 tmp1
drwxr-xrwx 2 user1 user1 4096 Feb 25 15:29 tmp2
drwxr-xrwx 2 user1 user1 4096 Feb 25 15:29 tmp3

Applying permissions on files/directory using the numeric values of the representations

There is another way applying permissions that is by using the permission representation values as in introduction. This can be done by just summing the values of the representations.

Example

[user1@linuxhelp Desktop]$ ll 
total 12
drwxr-xr-x 5 user1 user1 4096 Feb 25 15:29 dir1
-rwxrwxrwx 1 user1 user1   21 Feb 25 14:45 file1
-rw-r--r-- 1 user1 user1   29 Feb 25 14:46 file2
[user1@linuxhelp Desktop]$ chmod 765 file2 
[user1@linuxhelp Desktop]$ ll 
total 12
drwxr-xr-x 5 user1 user1 4096 Feb 25 15:29 dir1
-rwxrwxrwx 1 user1 user1   21 Feb 25 14:45 file1
-rwxrw-r-x 1 user1 user1   29 Feb 25 14:46 file2