checksecurity

apt-get install checksecurity

Just modify /etc/checksecurity.conf and files under /etc/checksecurity.

In fact, you just need to uncomment some lines. The default setup is will check diskfree, passwd, setuid and send report to root if something is wrong.

chkrootkit

apt-get install chkrootkit

Just modify /etc/chkrootkit.conf and set diff mode to true.

logcheck

apt-get install logcheck

Modify /etc/logcheck/logcheck.conf

sshd

Modify /etc/ssh/sshd_config to enhance security.

Doesn't allow password login.

For convinience, we allow root login. You may disable root login and configure su/sudo.

After modifying /etc/ssh/sshd_config, we need to reload the configuration file with:

service ssh reload

Then attempt a new ssh connection without breaking the previous one. Therefore, if we made some mistake in sshd_config, we can rollback to the original version.