Provavelmente, o arquivo tem o sinalizador imutável definido em seus atributos estendidos:
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
Para corrigir isso, basta executar 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 %