Command reference

Download a project and track changes to it. Also the easiest way to deploy a site to a server.

Syntax git clone url

Read and filter JSON in the terminal. AI services return JSON, so this comes up a lot.

Syntax jq 'filter' file

Open the manual page for a command. Read it before you run something an AI suggested.

Syntax man command

Show the status of NVIDIA GPUs: load, memory, and running processes. Useful for AI training jobs.

Syntax nvidia-smi

Download and run an open-weight language model on your own machine, after Ollama is installed.

Syntax ollama run model

Install Python libraries, including the ones used for machine learning.

Syntax pip install package

Create an isolated Python environment so project packages do not collide. Activate it with source .venv/bin/activate.

Syntax python3 -m venv .venv

Keep a terminal session alive after you disconnect. Good for long training or download jobs.

Syntax tmux new -s name

Change the current directory. cd with no argument takes you home; cd - jumps back to the last directory.

Syntax cd [directory]

Copy files. Use -r to copy a whole directory.

Syntax cp [-r] source destination

Show free and used disk space for each mounted filesystem.

Syntax df -h

Show how much disk space a file or directory uses.

Syntax du -sh path

Search for files by name, type, size, or age.

Syntax find path -name pattern

Create a symbolic link (a shortcut). Nginx uses these to enable a site.

Syntax ln -s target linkname

List the files in a directory. -l shows details, -a shows hidden files, -h makes sizes readable.

Syntax ls [options] [path]

Create a directory. -p also creates any missing parent directories.

Syntax mkdir [-p] directory

Move or rename a file or directory.

Syntax mv source destination

Print the full path of the directory you are in.

Syntax pwd

Delete files. There is no trash can, so check the path before you press Enter. -r deletes directories.

Syntax rm [-r] file

Bundle and compress files into one archive. Use -xzf to unpack it.

Syntax tar -czf archive.tar.gz directory

Make a web request from the terminal. -I shows only the headers; -s hides the progress bar.

Syntax curl [options] url

Look up DNS records. Handy for checking that a domain points at your server.

Syntax dig domain

Check that another machine answers. Press Ctrl+C to stop.

Syntax ping host

Copy only what changed between two folders, locally or over SSH.

Syntax rsync -av source/ destination/

Copy files to or from another machine over SSH.

Syntax scp source user@host:path

List the ports your machine is listening on and which programs own them.

Syntax ss -tulpn

Log in to another machine securely over the network.

Syntax ssh user@host

Simple firewall front end. Allow OpenSSH before you enable it, or you can lock yourself out.

Syntax sudo ufw command

Install, update, and remove software on Ubuntu and Debian.

Syntax sudo apt command

Read the logs that systemd collects. -f follows new entries.

Syntax journalctl -u service

Start, stop, restart, or check a service. Use status to see if it is running.

Syntax systemctl action service

Create a new user account with a home directory.

Syntax sudo adduser username

Change who can read, write, or run a file. 644 is typical for web files and 755 for scripts and directories.

Syntax chmod mode file

Change the owner and group of a file. Needed so the web server can read your site.

Syntax chown [-R] user:group path

Show a user's ID numbers and the groups they belong to.

Syntax id [user]

Run one command with administrator (root) privileges.

Syntax sudo command

Print the name of the user you are logged in as.

Syntax whoami

Show how much memory and swap is used and free.

Syntax free -h

Send a signal to a process. The default asks it to stop; -9 forces it to stop.

Syntax kill [-signal] PID

List running processes. Pipe it to grep to find one.

Syntax ps aux

Live view of CPU and memory use by process. Press q to quit.

Syntax top

Show how long the machine has been running and its recent load.

Syntax uptime

Pick out columns from text. $1 is the first column.

Syntax awk '{print $N}' file

Print the contents of a file. Also joins several files together.

Syntax cat file

Search inside files for lines that match a pattern. -r searches folders, -n shows line numbers, -i ignores case.

Syntax grep [options] pattern file

Show the first lines of a file (10 by default).

Syntax head [-n lines] file

Read a long file one screen at a time. Press q to quit and / to search.

Syntax less file

Find and replace text in a stream or file without opening an editor.

Syntax sed 's/old/new/g' file

Sort lines of text. -n sorts numbers, -r reverses the order.

Syntax sort [-n] [-r] file

Show the last lines of a file. -f keeps watching and prints new lines as they arrive.

Syntax tail [-f] [-n lines] file

Remove repeated neighboring lines. -c counts them. Usually used after sort.

Syntax uniq [-c]

Count lines, words, and bytes. wc -l counts lines.

Syntax wc [-l] file