Linux Command Reference

9 October 2025 · Updated 9 October 2025

commandslinuxbashshellreference

The snippets I’d otherwise have to look up.

systemd

Enable + start (or disable + stop) in one

sudo systemctl enable --now service-name
sudo systemctl disable --now service-name

Disable systemd-resolved

sudo systemctl disable systemd-resolved.service

For when port 53 needs to belong to something else.

SSH

Install a public key without `ssh-copy-id`

cat ~/.ssh/id_ed25519.pub | ssh user@remote-host "mkdir -p ~/.ssh && cat >> ~/.ssh/authorized_keys"

Fallback for stripped-down systems and appliances.

Docker

Validate a compose file without running it

docker compose config --quiet && printf "OK\n" || printf "ERROR\n"

Cheap pre-deploy sanity check.

Time and timezone

Sync hardware clock and set timezone

sudo hwclock --systohc
timedatectl set-timezone Australia/Melbourne

Databases

Initialise the MariaDB data directory

mariadb-install-db --user=mysql --basedir=/usr --datadir=/var/lib/mysql

First-time setup on Arch.

Image optimisation

Hardest PNG compression

optipng -o7 -zc9 <image>

-o7 is max optimisation, -zc9 is max zlib compression. Slow but worth it for static assets.

System maintenance

Disable the Ubuntu Pro nag

sudo mkdir /etc/apt/apt.conf.d/off
sudo mv /etc/apt/apt.conf.d/20apt-esm-hook.conf /etc/apt/apt.conf.d/off

MPD

Queue the entire library

mpc ls | mpc add

Update the music database

mpc update

Obscure but wonderful

Commands I keep rediscovering. Most aren’t installed by default.

`pv` — pipe viewer

tar c bigdir | pv | gzip > out.tar.gz

Live progress and throughput for any pipe.

`progress` — attach to already-running coreutils

progress -m

Scans /proc for active cp/mv/dd/tar and shows progress.

`sponge` — write back to the same file safely

sort file | sponge file
jq '.' messy.json | sponge messy.json

sort file > file truncates before reading. sponge buffers until stdin closes, then writes.

`ts` — timestamp lines from stdin

tail -f /var/log/syslog | ts '[%Y-%m-%d %H:%M:%.S]'

For logs and outputs that don’t include their own timestamps.

`vipe` — open `$EDITOR` mid-pipe

cat data.csv | vipe | jq -R 'split(",")'

Pauses the pipe in your editor. Whatever you save continues down the pipe.

`namei -lx` — walk every component of a path

namei -lx /var/www/html/secret.txt

Debug “permission denied” by seeing exactly which segment in the chain breaks.

`column -t` — auto-align tabular output

mount | column -t
cat /etc/passwd | column -t -s:

Use -s to set a separator other than whitespace.

`hyperfine` — proper command benchmarking

hyperfine --warmup 3 'fd pattern' 'find . -name "*pattern*"'

Runs commands repeatedly with statistical analysis and side-by-side comparison.

`watchexec` — run a command on file changes

watchexec -e rs cargo test
watchexec -w src 'npm run build'

The modern entr. Language-aware filters and sane defaults.

`socat` — Swiss army knife for sockets

# Forward port 8080 to an internal host
socat TCP-LISTEN:8080,fork TCP:internal-host:80

# Talk to the Docker socket interactively
socat - UNIX-CONNECT:/var/run/docker.sock

Forward anything to anything: TCP, UDP, Unix sockets, serial, files. Same syntax.

Tips

`sudo !!`

Re-run the last command with sudo.