In the case of Centos/RedHat OS, RPM tool can be used to verify the integrity of the installed package and check if any of the package has been compromised or not. RPM maintains a local database of all your packages installed in the system.
‘rpm -V packagename’ can be used to test package integrity. If anything has changed, it outputs with following symbols.
S = File size changed
M = File mode changed
5 = MD5 checksum changed
L = Symlink changed
U = Owner changed
G = Group changed
T = Modification time changed
c = it is a configuration file that has changed
missing = file is gone.
If the package is all good and nothing related to it has changed, then it won’t output anything.
This information helps us to know if anyone has replaced original binary files with some hacked binaries or if anything that is not supposed to be changed has been modified.
rpm -V sudo-1.7.2p1-22.el5
S.5….T c /etc/sudoers
Here, it indicates that a configuration file /etc/sudoers file that is related with sudo package has been modified. As a reason, its MD5 checksum has also changed.