Someone advised me to install a program called rkhunter for security. I've tried to do so, just using the apt command at the terminal, but am presented with a weird message about e-mail servers.

I have no idea what any of these options mean and so haven't dared to select any in case I gum up my Internet connection or something. What should I select?

It's possible that some other package called postfix, which was a required package that installed along with rkhunter, might be behind this rather than rkhunter itself. The word "postfix" appears on the menu.

Annoyingly, not only can I not get rkhunter going until this is completed, but it appears that dpkg is gummed up until it's completed and I can't install or uninstall anything else either!
Whenever I try to run, for instance, apt install, the terminal shows an error message referring to dpkg. After this has happened once or twice, it shows a different error message suggesting running "dpkg --configure -a".
When I do that, dpkg appears to sort itself out, but then, when I try to use apt install again (for any package), it goes back to trying to install rkhunter, scrolling through the usual "X% complete" messages and then displaying the cryptic menu, which cannot be closed until it is answered!

1 Answer 1


You are right, rkhunter wants a mail transport agent and it tries to install the large and complicated postfix to get one.

To avoid this, you can install the tiny nullmailer instead and that will satisfy the mail transport agent dependency. Once that's done, install rkhunter.

However, first you need to fix your dpkg problems. Please [edit] your question and give details about what's gone wrong there: error messages, etc.

  • Well, I can't, actually, because after remaining jammed for days no matter what I did, dpkg has for no apparent reason un-jammed itself, and rkhunter has spontaneously stopped asking the cryptic questions about servers and is working fine. So I didn't have a chance to try your instructions, but thanks all the same, would've been just what I was after if that hadn't happened. Am editing original posting to add details of what happened to dpkg in case anyone else strikes this glitch in future.
    – A. B.
    Mar 14, 2019 at 0:15

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