How to Make a File Write Protected in Linux

In Linux there is an additional file attribute which prevent files and folders from being deleted accidentally. Flag which make a file write/delete protected even from root is called immutable flag. Linux administrator must set this flag for various configuration files on the production servers so that no one could delete/temper with these files.

When you want to delete file/folder having immutable flag set, you will encounter with an error:
rm: cannot remove 'file-name': Operation not permitted.

Making file write protected in Linux

To set this flag we use plus (+) sign with chattr command and to unset this flag we use minus (-) sign.

Syntax:

To set this flag on files you can use the following command:

chattr +i filename

To unset or remove the attribute you can use the following command:

 chattr -i filename 

To set this flag on directories only you need to specify the directory name:

 chattr +i directory name 

chattr -i directory name 

How to search files having immutable flag set?
To accomplish this we use lsattr command pipe with the grep command.

lsattr -R | grep +i

Example:

Creating file having name san.txt and setting flag on it.
[oracle@orahow ~]$ vi san.txt

Initially check the file permission:
[oracle@orahow ~]$ ls -l san.txt
-rw-r--r-- 1 oracle dba 19 Nov 18 05:56 san.txt

 [oracle@orahow ~]$ chattr +i san.txt

chattr: Operation not permitted while setting flags on san.txt


To set this flag you need to login as a root user:

[root@orahow oracle]# chattr +i san.txt

[root@orahow oracle]# lsattr san.txt
----i-------- san.txt 

Now try to delete the file having immutable flag set:

[root@orahow oracle]# rm san.txt

rm: remove write-protected regular file `san.txt'? y

rm: cannot remove `san.txt': Operation not permitted

To remove this file you need to unset this flag:

[root@orahow oracle]# chattr -i san.txt

[root@orahow oracle]# lsattr san.txt

------------- san.txt

[root@orahow oracle]# rm san.txt
rm: remove regular file `san.txt'? y
[root@orahow oracle]# cat san.txt
cat: san.txt: No such file or directory

Making a directory write protected in Linux:

[root@orahow oracle]# mkdir san
[root@orahow oracle]# ls -ldr san

drwxr-xr-x 2 root root 4096 Nov 18 07:36 san

[root@orahow oracle]# chattr +i san

Now if you try to remove the directory it will throw a message: operation not permitted. Before deleting this folder you need to unset this flag.

[root@orahow oracle]# rmdir san
rmdir: san: Operation not permitted

[root@orahow oracle]# chattr -i san

[root@orahow oracle]# rmdir san

[root@orahow oracle]# ls -ldr san

ls: san: No such file or directory