RootKits enable a remote person to take control over your server. That's really bad !! You have to protect yourself against these attacks.
apt-get install rkhunter unhide
Update RootKit definitions
rkhunter --propupd rkhunter --update
Search for RootKits
You can search for any rootkit in your computer with rkhunter :
RootKit hunter [rkhunter] configuration
You can configure rkhunter :
To suppress the “Warning : the modules files ‘/proc/modules’ is missing” you need to add a skip test, line 246
DISABLE_TESTS="suspscan hidden_procs deleted_files packet_cap_apps apps os_specific"
According to your specific configuration, you need to adjust some specifics folders, line 438