From c589c89f60786e9377245bbea990dea2fe1415d1 Mon Sep 17 00:00:00 2001
From: Florian Obser <fobser@ripe.net>
Date: Wed, 26 Jul 2023 13:10:41 +0200
Subject: [PATCH] Mastodon Backup

---
 index.org           |   1 +
 mastodon-backup.org | 103 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 104 insertions(+)
 create mode 100644 mastodon-backup.org

diff --git a/index.org b/index.org
index 2fed422..b2a02ad 100644
--- a/index.org
+++ b/index.org
@@ -7,6 +7,7 @@
 + [[https://www.linkedin.com/in/florian-obser-75900383][Linkedin]]
 
 * Meditations
+- [[file:mastodon-backup.org][2023-07-26: Mastodon Backup]]
 - [[file:emacs-ietf.org][2023-04-05: Emacs IETF]]
 - [[file:dynamic_host_configuration_please.org][2023-03-07: Dynamic host configuration, please]]
 - [[file:privsep.org][2023-02-19: Privilege drop, privilege separation, and restricted-service operating mode in OpenBSD]]
diff --git a/mastodon-backup.org b/mastodon-backup.org
new file mode 100644
index 0000000..646df2e
--- /dev/null
+++ b/mastodon-backup.org
@@ -0,0 +1,103 @@
+#+TITLE: Mastodon Backup
+#+DATE: 2023-07-26
+* Prologue
+People on the Fediverse like to point out how you have to backup your
+data regularly in case of a catastrophic failure effecting your
+instance, the host of your instance, the data centre of your instance
+or maybe your admin. Heck, even a catastrophic failure effecting an
+admin of /another/ instance might make you wish you had a backup of
+your follows list[fn::If a remote admin decides to de-federate your
+instance it will sever all your connections with people on that
+instance.].
+
+Remembering to make a backup manually is already difficult
+enough[fn::My last manual backup was over a year old.], but then you
+also need to remember *how* to make that backup...
+* Manual Backups
+Got to "App Settings". You do not know where "App Settings" are? I
+know the feeling... They are behind the three cogs on the top
+left. Navigate to "Import and export". Click "Data export". Click the
+"CSV" link. Click the other "CSV" link. Click the other other "CSV"
+link. You have now downloaded your "follows", "muted" and "blocked"
+accounts lists.
+* Automatic Backups
+I have recently discovered [[https://toot.bezdomni.net/introduction.html][toot - Mastodon CLI client]] which can output
+a list of your follows and people following you. I have [[https://github.com/ihabunek/toot/pull/390][contributed
+code for "muted" and "blocked" commands]] which got accepted and
+released in version 0.38.
+
+We first need to authenticate to our instance by running ~toot
+login~. This is only needed once. For more information [[https://toot.bezdomni.net/usage.html][see the
+official documentation]].
+
+I am running the following script from cron once a day:
+#+begin_src shell
+  #! /bin/ksh
+  ACCOUNT=florian
+  INSTANCE=bsd.network
+  BACKUPDIR=/home/mastodonbackup/backup
+
+  set -e
+  set -o pipefail
+
+  exit_if_nonzero_or_stderr() {
+          (
+                  set -o pipefail
+                  { "$@" 1>&3 ;} 2>&1 | {
+                          if IFS= read -r line; then
+                                  printf "%s\n" "$line"
+                                  cat
+                                  exit 1
+                          fi
+                  } >&2
+          ) 3>&1
+  }
+
+  exit_if_nonzero_or_stderr /usr/local/bin/toot muted | \
+      awk '$2 !~ /^@.*@/ {print $2 "@'${INSTANCE}'"; next} {print $2}' \
+      > ${BACKUPDIR}/muted.new
+
+  mv ${BACKUPDIR}/muted{.new,}
+
+  exit_if_nonzero_or_stderr /usr/local/bin/toot blocked | \
+      awk '$2 !~ /^@.*@/ {print $2 "@'${INSTANCE}'"; next} {print $2}' \
+      > ${BACKUPDIR}/blocked.new
+  mv ${BACKUPDIR}/blocked{.new,}
+
+  exit_if_nonzero_or_stderr /usr/local/bin/toot following ${ACCOUNT} | \
+      awk '$2 !~ /^@.*@/ {print $2 "@'${INSTANCE}'"; next} {print $2}' \
+      > ${BACKUPDIR}/following.new
+  mv ${BACKUPDIR}/following{.new,}
+
+  exit_if_nonzero_or_stderr /usr/local/bin/toot followers ${ACCOUNT} | \
+      awk '$2 !~ /^@.*@/ {print $2 "@'${INSTANCE}'"; next} {print $2}' \
+      > ${BACKUPDIR}/followers.new
+  mv ${BACKUPDIR}/followers{.new,}
+#+end_src
+
+~toot~ outputs accounts from the local instance without
+/@instance/. ~awk(1)~ checks for the existence of two /@/ characters
+and if they are not present outputs /@instance@/ after the account
+name.
+
+Unfortunately ~toot~ always exits with 0, even if there is an error so
+we need to check if there is some output on =stderr= so that we do not
+replace our backup with empty files. For that I copy-pasted
+=exit_if_nonzero_or_stderr= from [[https://stackoverflow.com/a/61468182][stackoverflow]] like a pro.
+
+My crontab entry looks like this:
+#+begin_src crontab
+  ~ 9 * * * -sn su -s /bin/sh mastodonbackup -c /home/mastodonbackup/backup.sh
+#+end_src
+=-sn= ensures that the script is only run once and that no mail is
+sent after a successful run. See [[https://man.openbsd.org/crontab.5][crontab(5)]] for details.
+
+* Epilogue
+I have automated backing up the most important lists from my mastodon
+account. My mastodon account is running on somebody else's
+computer. The backup data is written as text files on a system that I
+control. That system is hooked up to my standard backup solution to
+have daily, multiple-redundant backups.
+
+I expire my toots after 90 days using [[https://ephemetoot.hugh.run/][ephemetoot]]. I have configured it
+to save the toots and media before deleting them from my account.