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How to lock down files in Linux using chattr

As system admins there is always a few trouble users that keep changing files we don’t want them to, such as /etc/resolv.conf. We can do that using the chattr command.

Here is the file with no flags using the lsattr command.

lsattr – list file attributes on a Linux second extended file system

$ lsattr resolv.conf
-------------e- resolv.conf

So lets lock down the file using -i (immutable) so that even root cannot make a change using the chattr command.

chattr – change file attributes on a Linux second extended file system

sudo chattr +i resolv.conf

Check our changes

$ lsattr resolv.conf
----i--------e- resolv.conf

Where we now see the i flag in the output. If we open the file we now see readonly at the bottom.

"resolv.conf" [readonly] 5L, 180C

So say we have to make a change to the file, easy enough using the chattr command again but instead of +i we use -i

sudo chattr -i resolv.conf

Check it with the lsattr command and we are back what we started with. So we can make the changes and then lock the file down again.

$ lsattr resolv.conf
-------------e- resolv.conf

So with just a few commands we can lock and unlock files on Linux.

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