Changing Ownership: "Operation not permitted" - even as root!

Solution 1:

Probably the file has the immutable flag set in its extended attributes:

user@user-X550CL ~/tmp % touch immutable
user@user-X550CL ~/tmp % sudo chown root:root immutable
[sudo] password for user:
user@user-X550CL ~/tmp % sudo chattr +i immutable
user@user-X550CL ~/tmp % lsattr immutable
----i--------e-- immutable
user@user-X550CL ~/tmp % sudo chown user:user immutable
chown: changing ownership of 'immutable': Operation not permitted

To fix this, just run sudo chattr -i file:

user@user-X550CL ~/tmp % sudo chattr -i immutable
user@user-X550CL ~/tmp % lsattr immutable
-------------e-- immutable
user@user-X550CL ~/tmp % sudo chown user:user immutable
user@user-X550CL ~/tmp %