Ubuntu 14.04… apt-get install “disk full” error (aaack!)

Recently we have been considering moving some MySQL database services from our cloud servers to Amazon RDS to simplify our management tasks, and wanted to run atop on some Ubuntu 14.04 LTS machines to get an initial sizing for RDS instances.

While trying to apt-get install  the atop package, I was getting a “disk full” error, but df -h said there were several GB’s left. It took a while to figure out the problem wasn’t disk space… I was out of inodes (basically, file handles.) Running df -i  showed 100% of the inodes were used up which has a similar result.  We monitor a lot of things, but inode usage was not one of them!

While figuring this out, I did manage to brick one of our servers, making this the day that all the work building our infrastructure with Chef paid off!  Instead of panicking and having to work all night, I was able to build and configure a new machine in just a few minutes.  But I digress.

The problem

Here’s what was going on:  Most of these servers have been running a while, and we apply all the linux/Ubuntu security updates regularly, and this often updates the linux kernel.  What we didn’t realize was that none of the old versions are ever automatically deleted.  We ended up with a /usr/src directory that looked like this:

And each version included a ton of individual inode-sucking files.  Finally some of the machines had gotten to the point where kernel updates were failing silently due to the inode shortage.

The solution

It turns out  apt  does not play well once something’s messed up, and as I said, subsequent fiddling bricked a machine before I figured out this solution.

We had to start by making some headroom using dpkg directly.  While you can shoot your foot off by deleting the kernel version you are using, and possibly recent ones, we had good success by starting with the oldest ones and only deleting a couple, like this:

etc… This ran ok and freed up enough inodes so we could run apt-get without disk full errors.  The autoremove option did all the work.

That removed the rest of the unused versions all at once, though we still had to manually “ok” a configuration option while uninstalling some of the packages.

From what I read, the default install of Ubuntu 16.04 LTS will default to removing old versions of kernels once they are not needed.  Until then, I’m writing this down in case it happens again!

basic_vsftpd cookbook for Chef

Recently I was rebuilding an old “virtual user” vsFTPd server, this time using Chef.  Of course I started by looking for a decent vsftpd cookbook.   There are several popular ones, for example:

  • The vsftpd “supermarket” cookbook might be fine for some users, but it’s not been updated since 2010, and it seems to lack a good way to override most of the default vsftpd.conf settings.
  • TheSerapher’s chef-vsftpd cookbook on github is popular but it’s opinionated with respect to defaults and seems to be aimed at setting up FTP for local users.

I was disappointed that these didn’t suit our needs, and a little bummed I wasted so much time reading the code to figure that out.  But by that time, I was so brushed up on vsftpd config that, against all advice, I started from scratch and created the basic_vsftpd cookbook.

My goal was to create a general purpose cookbook designed on three principles:

  • To be as simple as possible, only about installing vsftpd and nothing else
  • To let you create any possible vsftpd configuration
  • To set no defaults and make no assumptions about the intended use
  • OK, four.  Using code that’s easy to read and understand

In other words, the goal was to create a solid base recipe that is easy to use or extend via a wrapper cookbook.  The pleasing result was that after building/testing this cookbook, using it to deploy a real FTP server was a dream.  I’ve made this a public repo in hopes others will find it useful as well.

basic_vsftpd

“A basic and fully configurable cookbook for the vsftpd package.”  on github, and at the Chef supermarket.

Recipes

  • default – installs and configures the vsftpd package
  • chroot_list – Creates a chroot_list file for vsftpd
  • userlist – Creates a userlist file for vsftpd

Resources

  • user_conf – Creates a user configuration file in the vsftpd user_config_dir directory

Authenticating vsFTPd virtual users with pam_pwdfile.so

For years, the standard way to set up password authentication for vsFTPd FTP server was to use PAM with the pam_userdb.so module.  It looks great on paper, but if you have tried this, you know that generating a Berkeley DB password file is a PITA, debugging is blind and brutal, and password file generation does not play well with automated deployments.  On top of that, it turns out that pam_userdb.so is (apparently) being phased out of the PAM package.

I stumbled across the pam_pwdfile.so module and it worked for us without all the confusing dead-ends we got with userdb. This module seems to be supported long-term, and uses an htpasswd-like password file. Here’s how to set it up, in four steps:

Installing pam_pwdfile.so

We’re using Ubuntu 14.04 at the moment, and you must install this module as a package:

or in a chef recipe, simply:

Creating a PAM service

Create this file at /etc/pam.d/vsftpd

This creates a “PAM service” named vsftpd.   The debug option dumps some extra info to /var/log/auth.log and is very helpful in getting things set up the first time.  The pwdfile= option denotes the filename of the user/pw database we’ll create next.

Configuring vsFTPd

To use this new service, just add the following option to /etc/vsftpd.conf.

Creating the user/password file

This is the payoff.  There are a couple ways to generate the password file.  From the command line you can user the Apache htpasswd utility, and there seems to be a number of other tools to generate these files as well.

But we’re deploying with Chef and it would be great to be able to automate our deployment, and with this file format we can do it. The key here is to know you can create a properly-hashed password using  openssl passwd -1 mypa$$w0rd . Here’s an example of how to create the whole pwdfile in a Chef recipe:

That’s it.  VIrtual users should now be able to log in using passwords hashed in the passwd file.  (I’m assuming the rest of the vsFTPd configuration supports using virtual users.  This can be a can of worms to get it set up the way you want, but is beyond the scope of this post.)

Troubleshooting

First off, don’t forget to restart the vsftpd service after all the changes… and make sure it starts!  A common issue is that certain config error seem to send vsftpd into a restart loop and the system kills it.  So your start messages looks good but then it dies.

In my experience, the most likely problem here will be with the vsftpd setup and not the authentication.  To effectively “stub out” the authentication, temporarily replace the /etc/pam.d/vsftpd file with this:

This allows any user/pw to log in.  If you cannot log in now, your problem is with vsFTPd, your firewall, etc.  (Don’t forget that this leaves the FTP server wide open!)

For PAM problems, the debug option in the pam service file is helpful, as is just watching the FTP connection/login conversation.

Good luck.  I hope this saves you some of the 8+ hours we spent screwing with promising “solutions” that did not work!

Deploying MediaWiki via Chef

After deploying a few custom servers to support both Ruby and php applications, setting up a server to run MediaWiki seemed like a breeze.  And it is, sort of, so long as you know where to draw the line.

It seemed plausible to create a Chef cookbook to deploy a ready-to-run MediaWiki installation.  And I wasted a lot of time trying.  At first I was delighted that there was so much setup documentation, but as I dug  in to it, I realized that it was virtually all written for a barely-technical audience. Important details were missing and once you got outside the “recommended” web-based install directions, there were even factual errors.

So after trying a number of things,  documented and undocumented, I finally conceded that the only really supported way to do an install is using the web install method that MediaWiki provides.  It’s a shame really, since all it does is set up the database and create the LocalSettings.php file.  But the docs are simply not sufficient to support automating anything further.

Here’s what works

You can use Chef to set up:

  • the basic server niceties, like a firewall, email support for crontab jobs, and the like
  • the basic LAMP stack and php using the supported apache2, php and mysql cookbooks
  • MySQL users and create the database.  While the MediaWiki installer would create the production MySQL user and database for you, there’s no harm in letting Chef do it first, and the value is that Chef will maintain the resources.
  • the MediaWiki image and initial files.  I automated pulling the MediaWiki tar file, and expanding it into the public www directory, with a guard to prevent if it already exists.

But that’s all!  Efforts to build out the database using the MediaWiki scripts failed, and the LocalSettings.php file just seems to require manual editing whatever you do.  So after the Chef build you still have to run the web-based setup, and copy (and probably edit)  the generated LocalSettings.php back to the document root directory of the site.

That’s not how we like to roll here… it’s not terrible but it’s a step backwards toward the manual setup + “servers as pets” thing, and for now we’re stuck with it.

Update: it gets worse

After backing off from trying to automate any actual MediaWiki installation, I thought I was out of the woods.  Since I was planning to add Semantic MediaWiki and Semantic Forms, I thought it would be OK to install these packages using Composer as part of the server build.  (Nope) That results in an immediate error when trying to run the MediaWiki web-based installer.

So now my “automated” install has to work like this:

  • Use Chef to converge a new server
  • Run the manual web-based MediaWiki installer
  • Copy the LocalSettings.php file back up to the new server
  • Manually add the extensions I want to use via php Composer (and any other required install steps, including a frequent requirement to edit the LocalSettings.php file.)

It’s really not looking much like an automated solution anymore, but that seems like the best I can do.  After using tools like Chef and Capistrano for deployment, I am finding the process for installing MediaWiki to be rather unsatisfying.

 

What’s Wrong with Chef and Other Rants

My apologies, this is a placeholder for a number of things I have meant to write about using Chef to deploy our cloud servers.  It turns out the task took longer and was a lot more convoluted than imagined, even after considering Hofstadter’s Law, so the writing has all been pushed back.  But here’s the proposed list of topics worth writing (& reading) about:

Last first, since it is current.