Migrating mastodon to Debian 11 Bullseye: fixing the segfault

In trying to upgrade a Raspberry Pi 4 from Debian 10 Buster to Debian 11 Bullseye, I made some mistakes, and basically shot my installation to pieces.

It ran, but I had absolutely no faith in it surviving a reboot.

Now that I have a working image for the Debian 11 Bullseye- based 64 bit "lite" Raspberry Pi OS, I was keen to move mastodon across to the new machine.

I've migrated mastodon before, and it was pretty painless: a new installation, a database dump and restore, and moving some system files.

The official mastodon migration instructions are reasonably good, if a bit confusing in their layout - you need to jump from basic to detailed, and then remember to go back to the basic instructions again. (I've made a pull request to the docs about this; let's see.) But they do work.

Well, they did.

This time, they did not.

Fixing the segmentation fault

When I ran:

RAILS_ENV=production bundle exec rails assets:precompile

it resulted in several thousand lines of error message, with the crucial bit being:

/home/mastodon/live/vendor/bundle/ruby/2.7.0/gems/ffi-1.15.0/lib/ffi/library.rb:112: [BUG] Segmentation fault at 0x000000000005c6b0

Bugger.

Fortunately, I found that someone else had had a similar problem on Debian 11 and, even better, they had a solution.

Changing the systemd service definitions was fine, but the command it suggests you run:

LD_PRELOAD=libjemalloc.so RAILS_ENV=production bundle exec rake mastodon:setup

is for a new installation. Not a migration.

For a migration, you would normally run:

RAILS_ENV=production bundle exec rails assets:precompile
RAILS_ENV=production ./bin/tootctl feeds build

so I modified them using the same approach:

LD_PRELOAD=libjemalloc.so RAILS_ENV=production bundle exec rails assets:precompile
LD_PRELOAD=libjemalloc.so RAILS_ENV=production ./bin/tootctl feeds build

and that did the trick. The revised commands ran successfully, without segfaulting.


Author: neil

I'm Neil. By day, I run a law firm, decoded.legal, giving advice on Internet, telecoms, and tech law. This is my personal blog, so will be mostly about tech stuff, cycling, and other hobbies.

You can find me (and follow me) on Mastodon and Twitter.