Backup and Restore Guide

Docker and Ansible

When using docker or ansible, there should be a volumes folder, which contains both the database, and all the pictures. Copy this folder to the new instance to restore your data.

Full Database backup

To take a complete backup of the DB to a .sql.gz file, you can run:

docker compose exec postgres pg_dumpall -c -U lemmy | gzip > lemmy_dump_`date +%Y-%m-%d"_"%H_%M_%S`.sql.gz

For compression, you can use either gzip and gunzip, or xz and unxz.

A Sample backup script

#!/bin/sh
# DB Backup
ssh MY_USER@MY_IP "docker compose exec postgres pg_dumpall -c -U lemmy" | gzip > ~/BACKUP_LOCATION/INSTANCE_NAME_dump_`date +%Y-%m-%d"_"%H_%M_%S`.sql.gz

# Volumes folder Backup
rsync -avP -zz --rsync-path="sudo rsync" MY_USER@MY_IP:/LEMMY_LOCATION/volumes ~/BACKUP_LOCATION/FOLDERNAME

Restoring the DB

To restore, run:

docker compose up -d postgres

# Restore from the .sql.gz backup
gunzip < db_dump.sql  |  docker compose exec -T postgres psql -U lemmy

# Note: You may need to change the permissions on the postgres directory, depending on your system.
chown -R $USER volumes
docker compose restart postgres

# Continue with the startup
docker compose up -d

If you've accidentally already started the lemmy service, you need to clear out your existing database:

# Drop the existing DB
docker exec -i FOLDERNAME_postgres_1 psql -U lemmy -c "DROP SCHEMA public CASCADE; CREATE SCHEMA public;"

# This also might be necessary when doing a db import with a different password.
docker exec -i FOLDERNAME_postgres_1 psql -U lemmy -c "alter user lemmy with password 'bleh'"

Then run the restore commands above.

Changing your domain name

If you haven't federated yet, you can change your domain name in the DB. Warning: do not do this after you've federated, or it will break federation.

Get into psql for your docker:

docker compose exec postgres psql -U lemmy

-- Instance
update instance set domain = replace (domain, 'old_domain', 'new_domain');

-- Site
update site set actor_id = replace (actor_id, 'old_domain', 'new_domain');
update site set inbox_url = replace (inbox_url, 'old_domain', 'new_domain');
update site set sidebar = replace (sidebar, 'old_domain', 'new_domain');

-- Post
update post set ap_id = replace (ap_id, 'old_domain', 'new_domain');
update post set url = replace (url, 'old_domain', 'new_domain');
update post set body = replace (body, 'old_domain', 'new_domain');
update post set thumbnail_url = replace (thumbnail_url, 'old_domain', 'new_domain');

-- Comments
update comment set ap_id = replace (ap_id, 'old_domain', 'new_domain');
update comment set content = replace (content, 'old_domain', 'new_domain');

-- Private messages
update private_message set ap_id = replace (ap_id, 'old_domain', 'new_domain');
update private_message set content = replace (content, 'old_domain', 'new_domain');

-- User
update person set actor_id = replace (actor_id, 'old_domain', 'new_domain');
update person set inbox_url = replace (inbox_url, 'old_domain', 'new_domain');
update person set shared_inbox_url = replace (shared_inbox_url, 'old_domain', 'new_domain');
update person set bio = replace (bio, 'old_domain', 'new_domain');
update person set avatar = replace (avatar, 'old_domain', 'new_domain');
update person set banner = replace (banner, 'old_domain', 'new_domain');

-- Community
update community set actor_id = replace (actor_id, 'old_domain', 'new_domain');
update community set followers_url = replace (followers_url, 'old_domain', 'new_domain');
update community set inbox_url = replace (inbox_url, 'old_domain', 'new_domain');
update community set shared_inbox_url = replace (shared_inbox_url, 'old_domain', 'new_domain');
update community set moderators_url = replace (moderators_url, 'old_domain', 'new_domain');
update community set featured_url = replace (featured_url, 'old_domain', 'new_domain');
update community set description = replace (description, 'old_domain', 'new_domain');
update community set icon = replace (icon, 'old_domain', 'new_domain');
update community set banner = replace (banner, 'old_domain', 'new_domain');

--- Custom Emoji
update custom_emoji set image_url = replace (image_url, 'old_domain', 'new_domain');

More resources

• https://stackoverflow.com/questions/24718706/backup-restore-a-dockerized-postgresql-database