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Temporary exile

Server Breakage and Rebirth

Now that I’ve caught up on the work I missed yesterday, now seems like a good time to write about the massively bad server blowout I had yesterday. Since my laptop’s upgrade from Debian Lenny to Squeeze went so well, I got a little cavalier and was sloppy when doing a dist-upgrade on a server on which I had done some heavy-configuration. The summarized story is that I borked a kernel dependency and actually suceeded in breaking the packaging system on that machine, a first for me in at least the most recent four-five years. Notice, still, that the breakage was caused by me and not by the most-excellent Debian package management tools. It worked out for the better as I had been sort-of-almost-definately been meaning to rebuild that particular machine anyway. Since the hardware is fine (though the disk might die, soonish), I reinstalled Debian Squeeze from a nightly-build installer and took the opportunity to change a few things in my network’s setup. The first major change I made was to switch all the machines on my network to use debtorrent instead of apt-proxy which had been behaving unreliably. In particular, apt-proxy had been randomly hanging after a few transfers, thus causing the machines using it to be unable to upgrade their packages or install new ones. So, in an attempt to fix it and give a little back to the community, I have installed debtorrent on my main server and configured my other machines to use it. So far, it’s working quite well, the download speed is rather fast and it caches packages so that other machines may download them. The next thing I changed was to take a few more security measures than I normally do. I have been using various known strategies for some time now but a fresh start seemed like a good opportunity to tighten things up with a fresh install. First, the Securing Debian manual is required reading for any sysadmin and I re-read over it while waiting for lengthy processes to finish. Since my machines are already behind a firewall that only lets SSH traffic in and then only through to the server in question, my revised security checklist goes something like this: 1. Remove all RPC services:

`sudo aptitude --purge remove portmap nfs-common`
  1. Remove root login option (especially since I disable the root account) from /etc/ssh/sshd_config by making sure that the relevant line reads PermitRootLogin no and then restarting ssh
  2. Installing some harden packages: sudo aptitude install harden-servers harden-clients harden-tools
  3. Installing some helpful security packages: sudo aptitude install debsums logcheck denyhosts chkrootkit and then doing a dpkg-reconfigure on debsums to make sure it does a daily integrity check and altering the denyhosts config file to make it sync with the global denyhosts database (this helped cut down on automated ssh attacks tremendously)
  4. One of the most important things to do is also to make sure that you get your local mail delivered so that you can see status reports. I do a sudo dpkg-reconfigure exim4-config to make certain everything is as I like it and that no holes are left open but I still get my system mail.
  5. The last thing that I’ll do is to install nmap and scan myself to see what’s showing. For this particular box, I saw nothing but SSH and SMTP from the box itself and nothing but SSH from the outside. Good.

There might be a few other things which I do but I can’t recall them now. I would install SELinux but my understanding (according to the Debian Wiki) is that it’s still in the experimental stage so I won’t move on that just yet. Is there something huge and obvious that I’m forgetting security wise? Is a file-integrity checker going to be useful if I have constantly-changing and files and I am continually-updating packages? The other major change is that I moved from the XFS filesystem back to ext3 with the intention of soon trying the upgrade-in-place features found in ext4 now that it’s got so many things which I liked about XFS. Since the Debian installer didn’t present me with an option to use ext4, this seemed like the best idea. Was I very wrong? As a side note, I tried out weechat on the console for about an hour before immediately going back to ERC on Emacs because it integrates so well with my alltime favorite editor.

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