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Writer's pictureMukesh Chanderia

Linux - Commands Part 10 - User Permission

Updated: Aug 21, 2021

1) Permissions : Read, Write & Execute


Read (r) : 4

Write (w) : 2

Execute (x) : 1 --> If this is on directory then user can go inside folder and list and if on script file then user can run script.


Here "d" represents directory


2) Mukesh user went to /tmp and created dir "mukesh"


[mukesh@RedHat mukesh]$ ls -ld /tmp/mukesh


d rwx rwx r-x. 2 mukesh mukesh 24 Jan 20 12:16 /tmp/mukesh


[mukesh@RedHat mukesh]$ ls -ld /tmp/mukesh/mukeshlife

-rw -rw- r--. 1 mukesh mukesh 0 Jan 20 12:16 /tmp/mukesh/mukeshlife


Now user adminji can read file mukeshlife but can't modify it.


3) If user mukesh assign write permission to others then user "adminji" can modify file "mukeshlife"


[mukesh@RedHat mukesh]$ chmod o+w mukeshlife


4) Another way to provide permission


chmod o=rwx /tmp/mukesh

[mukesh@RedHat mukesh]$ ls -ld /tmp/mukesh

drwxrwxrwx. 2 mukesh mukesh 24 Jan 20 12:16 /tmp/mukesh


5) To add user to group


usermod -G Groupname user

Add or remove permission from group from directory

chmod g+w /devteam

chmod g-w /devteam

chmod g=--- /devteam


Now create a group

groupadd newgroup

now make this group owner of a directory

chgrp newgroup /tmp/mukesh


To change owner of directory

chown user directory


To change owner and groupowner in one command of a particular directory.

chown user:group directory


To change owner group and other permission in one command

chmod u=--- ,g=--- ,o=---


To provide same command to owner group and other

chmod ugo=rwx directory

chmod -x directory or chmod +x directory


Now use numeric method to give permission

chmod 755 directory / file



[mukesh@RedHat mukesh]$ ls -ld /tmp/mukesh

drwxrwxrwx. 2 mukesh mukesh 24 Jan 20 12:16 /tmp/mukesh


[mukesh@RedHat mukesh]$ chmod 700 /tmp/mukesh

[mukesh@RedHat mukesh]$ ls -ld /tmp/mukesh

drwx------. 2 mukesh mukesh 24 Jan 20 12:16 /tmp/mukesh


Now the permission of file mukeshlife inside folder mukesh hasn't changed.

[mukesh@RedHat mukesh]$ ls -l /tmp/mukesh/mukeshlife

-rw-rw-rw-. 1 mukesh mukesh 8 Jan 20 12:26 mukeshlife


Note : If we use "R" while changing permission on the directory then it will change permission of all files and folders inside this directory to of parent.



[mukesh@RedHat mukesh]$ chmod 700 -R /tmp/mukesh

[mukesh@RedHat mukesh]$ ls -ld /tmp/mukesh/mukeshlife

-rwx------. 1 mukesh mukesh 8 Jan 20 12:26 /tmp/mukesh/mukeshlife


[root@RedHat adminji]# groupadd monu

[root@RedHat adminji]# chgrp monu /tmp/mukesh

[mukesh@RedHat mukesh]$ ls -ld /tmp/mukesh *

-rwx------. 1 mukesh mukesh 8 Jan 20 12:26 mukeshlife

drwx------. 2 mukesh monu 24 Jan 20 12:16 /tmp/mukesh


[root@RedHat adminji]# chgrp monu -R /tmp/mukesh

[mukesh@RedHat mukesh]$ ls -ld /tmp/mukesh *

-rwx------. 1 mukesh monu 8 Jan 20 12:26 mukeshlife

drwx------. 2 mukesh monu 24 Jan 20 12:16 /tmp/mukesh


This change in permission on group or changing group owner doesn't work for new files added in directory.

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