this post was submitted on 05 Oct 2023
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Need help understanding a back-up script (lemmy.world)
submitted 1 year ago by Natal@lemmy.world to c/selfhosted@lemmy.world
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Hello everyone!

I had a container with a DB crap itself yesterday so I'm trying to speed up my learning to back up stuff.

I came across a script that taught me how to back-up a containerized postgres db at given intervals and it works. I managed to create db dumps and restore them. I've documented everything and now my whole docker-compose/env etc are on git control.

There's one part of the script I don't decypher but I'd like to maybe change it. It is about the number of back-up copies.

Here's the line from the tutorial: ls -1 /backup/*.dump | head -n -2 | xargs rm -f

Can someone explain to me what this line does? I'd like to keep maybe 3 copies just in case the auto-backup backs up a rotten one.

Thanks!

Full code below:

backup:
    image: postgres:13
    depends_on:
      - db_recipes
    volumes:
      - ./backup:/backup
    command: >
      bash -c "while true; do
        PGPASSWORD=$$POSTGRES_PASSWORD pg_dump -h db-postgresql -U $$POSTGRES_USER -Fc $$POSTGRES_DB > /backup/$$(date +%Y-%m-%d-%H-%M-%S).dump
        echo ""Backup done at $$(date +%Y-%m-%d_%H:%M:%S)""
        ls -1 /backup/*.dump | head -n -2 | xargs rm -f
        sleep 86400
      done"
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[–] smileyhead@discuss.tchncs.de 2 points 1 year ago

Backups are created to /backup directory and are ended with .dump file extention.

ls -1 is listing all those files chronologically, -1 is to keep one file per one line.

head -n -2 is getting lines from the top to the last two at bottom.

xargs rm -f is calling rm -f on every line of the input.

| is pipe symbol, that gets output from command before and gives it to command after

So TLDR it's removing all backups except the last 2 ones.