Monthly Archives: June 2017

First Experiences with Stretch

Uncategorized

I’ve done my first upgrades to Debian stretch at this point. The results have been overall good. On the laptop my kids use, I helped my 10-year-old do it, and it worked flawlessly. On my workstation, I got a kernel panic on boot. Hmm.

Unfortunately, my system has to use the nv drivers, which leaves me with an 80×25 text console. It took some finagling (break=init in grub, then manually insmoding the appropriate stuff based on modules.dep for nouveau), but finally I got a console so I could see what was breaking. It appeared that init was crashing because it couldn’t find liblz4. A little digging shows that liblz4 is in /usr, and /usr wasn’t mounted. I’ve filed the bug on systemd-sysv for this.

I run root on ZFS, and further digging revealed that I had datasets named like this:

  • tank/hostname-1/ROOT
  • tank/hostname-1/usr
  • tank/hostname-1/var

This used to be fine. The mountpoint property of the usr dataset put it at /usr without incident. But it turns out that this won’t work now, unless I set ZFS_INITRD_ADDITIONAL_DATASETS in /etc/default/zfs for some reason. So I renamed them so usr was under ROOT, and then the system booted.

Then I ran samba not liking something in my bind interfaces line (to be fair, it did still say eth0 instead of br0). rpcbind was failing in postinst, though a reboot seems to have helped that. More annoying was that I had trouble logging into my system because resolv.conf was left empty (despite dns-* entries in /etc/network/interfaces and the presence of resolvconf). I eventually repaired that, and found that it kept removing my “search” line. Eventually I removed resolvconf.

Then mariadb’s postinst was silently failing. I eventually discovered it was sending info to syslog (odd), and /etc/init.d/apparmor teardown let it complete properly. It seems like there may have been an outdated /etc/apparmor.d/cache/usr.sbin.mysql out there for some reason.

Then there was XFCE. I use it with xmonad, and the session startup was really wonky. I had to zap my sessions, my panel config, etc. and start anew. I am still not entirely sure I have it right, but I at do have a usable system now.

Fixing the Problems with Docker Images

Linux, Programming

I recently wrote about the challenges in securing Docker container contents, and in particular with keeping up-to-date with security patches from all over the Internet.

Today I want to fix that.

Besides security, there is a second problem: the common way of running things in Docker pretends to provide a traditional POSIX API and environment, but really doesn’t. This is a big deal.

Before diving into that, I want to explain something: I have often heard it said the Docker provides single-process containers. This is unambiguously false in almost every case. Any time you have a shell script inside Docker that calls cp or even ls, you are running a second process. Web servers from Apache to whatever else use processes or threads of various types to service multiple connections at once. Many Docker containers are single-application, but a process is a core part of the POSIX API, and very little software would work if it was limited to a single process. So this is my little plea for more precise language. OK, soapbox mode off.

Now then, in a traditional Linux environment, besides your application, there are other key components of the system. These are usually missing in Docker containers.

So today, I will fix this also.

In my docker-debian-base images, I have prepared a system that still has only 11MB RAM overhead, makes minimal changes on top of Debian, and yet provides a very complete environment and API. Here’s what you get:

  • A real init system, capable of running standard startup scripts without modification, and solving the nasty Docker zombie reaping problem.
  • Working syslog, which can either export all logs to Docker’s logging infrastructure, or keep them within the container, depending on your preferences.
  • Working real schedulers (cron, anacron, and at), plus at least the standard logrotate utility to help prevent log files inside the container from becoming huge.

The above goes into my “minimal” image. Additional images add layers on top of it, and here are some of the features they add:

  • A real SMTP agent (exim4-daemon-light) so that cron and friends can actually send you mail
  • SSH client and server (optionally exposed to the Internet)
  • Automatic security patching via unattended-upgrades and needsrestart

All of the above, including the optional features, has an 11MB overhead on start. Not bad for so much, right?

From here, you can layer on top all your usual Dockery things. You can still run one application per container. But you can now make sure your disk doesn’t fill up from logs, run your database vacuuming commands at will, have your blog download its RSS feeds every few minutes, etc — all from within the container, as it should be. Furthermore, you don’t have to reinvent the wheel, because Debian already ships with things to take care of a lot of this out of the box — and now those tools will just work.

There is some popular work done in this area already by phusion’s baseimage-docker. However, I made my own for these reasons:

  • I wanted something based on Debian rather than Ubuntu
  • By using sysvinit rather than runit, the OS default init scripts can be used unmodified, reducing the administrative burden on container builders
  • Phusion’s system is, for some reason, not auto-built on the Docker hub. Mine is, so it will be automatically revised whenever the underlying Debian system, or the Github repository, is.

Finally a word on the choice to use sysvinit. It would have been simpler to use systemd here, since it is the default in Debian these days. Unfortunately, systemd requires you to poke some holes in the Docker security model, as well as mount a cgroups filesystem from the host. I didn’t consider this acceptable, and sysvinit ran without these workarounds, so I went with it.

With all this, Docker becomes a viable replacement for KVM for various services on my internal networks. I’ll be writing about that later.

Family Spring: A Story in Photos

Family, Travel

This has been a spring with times to relax, times to be busy, times of anticipation of a new baby, and times of enjoying our family.

Rather than write a lot of words about it, I’m telling the story in photos.

To view, click here, then click Show Info in the upper right to see captions. You can pause it with the button in the lower left, and use arrow keys to advance.

Alternatively, there’s a captionless slideshow available here.

Here’s one photo to get you started:

Happy about the little sister on the way

Flying with my brothers

Aviation, Family, Travel

Picture one Sunday morning. Three guys are seemingly-randomly walking into a Mennonite church in rural Nebraska. One with long hair and well-maintained clothes from the 70s. Another dressed well enough to be preaching. And the third simply dressed to be comfortable, with short hair showing evidence of having worn a headset for a couple of hours that morning. This was the scene as we made a spur-of-the-moment visit to that church — which resulted in quite some surprise all around, since my brother knew a number of people there.

For instance:

Pastor: Peter! What are you doing here?

Peter: [jokingly] Is that how you greet visitors here?

And then, of course, Peter would say, “Well, we were flying home from South Dakota and figured we’d stop in at Beatrice for fuel. And drop in on you.” Followed by some surprise that we would stop at their little airport (which is quite a nice one).

This all happened because it was windy. This is the fun adventure of aviation. Sometimes you plan to go to Texas, but the weather there is terrible, so you discover a 100-year-old landmark in Indiana instead. Or sometimes, like a couple of weeks ago, we planned to fly straight home but spent a few hours exploring rural Nebraska.

The three of us flew to Sioux Falls, SD, in a little Cessna to visit my uncle and aunt up there. On our flight up, we stopped at the little airport in Seward, NE. It was complete with this unique elevated deck. In my imagination, this is used for people to drink beer while watching the planes land.

IMG_20170512_113323

In South Dakota, we had a weekend full of card and board games, horseshoes, and Crokinole with my uncle and aunt, who are always fun to visit. We had many memories of visits up there as children — and the pleasant enjoyment of the fact that we didn’t need an 8-hour drive to get there. We flew back with a huge bag of large rhubarb from their garden (that too is something of a tradition!)

It was a fun weekend to spend with my brothers — first time we’d been able to do this in a long while. And it marked the 11th state I’ve flown into, and over 17,000 miles of flying.