Linux

A collection of notes on using Linux systems, in particular Ubuntu.

Package Management

List all installed packages

# List everything
sudo dpkg -l

# List things with apache in the name
sudo dpkg -l | grep apache

SSH

SSH Keys

Generate an ssh-key for every client

ssh-keygen -t ed25519 -a 100 [-C "comment your client name"] [-f output_path]

Some older software such as Solid file explorer require RSA keys in PEM key format

ssh-keygen -t rsa -b 4096 -a 100 -m PEM [-C "comment your client name"] [-f output_path]

You can also convert existing keys to PEM format

ssh-keygen -p -m PEM [-C "comment your client name"] [-f output_path]

Manage ssh keys

# On the client
ssh-copy-id [email protected]

# On the server
vim ~/.ssh/authorized_keys

Notes:

• According to this you should avoid using ECDSA and DSA keys.

Port Forwarding

Also: SSH Tunneling, SSH Proxy, SSH Reverse Proxy
If you need to access a port on the remote computer, you can use the -L option to forward ports from the remote to the local machine.

ssh -L <localport>:localhost:<remoteport> <remoteurl>
# E.g. ssh -L 8080:localhost:80 [email protected]

You can also do the reverse, giving the remote access to a local port using -R

ssh -R <localport>:host:<remoteport> <remoteurl>
# E.g. ssh -R 8080:localhost:80 [email protected]

VNC

x11vnc

Reference I recommend not exposing VNC. Set it to localhost only and use ssh port forwarding.

Remmina

How to use Remmina to connect to over ssh tunnel

Nvidia

Switching between Nvidia and Intel

Reference
Make sure the Nvidia graphics drivers are installed. Then you can select between Nvidia and Intel GPUs using the Nvidia X Server Settings application nvidia-settings. Alternatively, you can use the following commands in the terminal.
To switch to the Nvidia GPU:

sudo prime-select nvidia

To switch back to the Intel GPU:

sudo prime-select intel

prime-select query will print either nvidia or intel to stdout.

Environment Variables

Ubuntu Help Reference

Tmux

Tmux cheat sheet
Tmux, or Terminal Multiplexer is an alternative to screen.
Use it to keep terminals open and tasks running after you disconnect your SSH connection.
Getting Started:

# Make a new session
tmux
# Make a new named session
tmux new -s my_session
# Rename a session
# Keybinding: Ctrl + b, $
tmux rename-session [-t current-name] [new-name]
# Detach from a session
# Keybinding: Ctrl + b, d
tmux detach
# List windows
tmux ls
# Attach to a session
tmux attach -t my_session

File Manager

Add to context menu

Link

Etcher

Github
Installing etcher

echo "deb https://deb.etcher.io stable etcher" | sudo tee /etc/apt/sources.list.d/balena-etcher.list
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 379CE192D401AB61
sudo apt update
sudo apt install balena-etcher-electron

Logs

Logs are stored under /var/log. These can end up taking up a lot of space.
You can delete logs in the journal folder Reference

Default gcc/g++ version

See https://askubuntu.com/questions/26498/how-to-choose-the-default-gcc-and-g-version.