Useful Linux / Debian / Ubuntu commands and stuff

linux-debian-ubuntu.md

Create a relatively minimal, SSH-automation-capable user

adduser --disabled-login --comment "" SomeUserName

• adduser: friendlier front-end for useradd, usermod and groupadd
• --disabled-login: no password and shell set to /usr/sbin/nologin
• --comment "": don't prompt for details, successor of deprecated --gecos flag i think

Create custom sudoers entry safely

Only needed if a user needs to run a command as root/sudo (e.g. not needed for zfs send/syncoid when setting it up rootless with zfs allow)

visudo /etc/sudoers.d/SomeUserName
(better than just visudo because of package manager upgrades)

To check sudoers configuration (above command won't check permissions by default):
visudo --check --strict

Example syncoid backup script

#!/bin/bash
/usr/sbin/syncoid \
  --sendoptions=w # send raw/encrypted
  --no-privilege-elevation \ # don't attempt to use root/sudo (assumes proper permissions / zfs allow)
  --no-sync-snap \ # don't create a snapshot for this sync (would require additional permissions, i skip this because sanoid already creates plenty of snapshots)
  --pv-options='-L 5M' \ # optional: limit bandwidth to 5MB/s 
  tank/source-dataset SomeUser@SomeServer:tank/target-dataset

Minimalistic, IP-limited authorized_keys entry to run a single command

from="192.168.0.0/24",restrict,command="SomeCommandHere" ssh-[...] [key] user@host

Prevent locale issues with SSH

ssh -F ~/.ssh/config user@ip
-F forces usage of the config, skipping global config which attempts to send locales.
Source: https://stackoverflow.com/a/41786965

Inline Docker file to build a container as part of a docker compose.yaml

services:
  app:
    build:
      context: .
      dockerfile_inline: |
        FROM baseimage ...

Grow Ubuntu VM on Proxmox

1. grow VM disk on Proxmox
2. in VM: growpart [device] [partitionNumber] (e.g. growpart /dev/sda 2)
3. in VM: resize2fs [partition] (e.g. resize2fs /dev/sda2)
4. verify with df -h