More Common Tasks On Linux

On this page are my best-known-practice routines for anything that didn’t make the main Linux cheatsheet.

I chose to break these out into a separate page because I felt like these are still worth summarizing in some way, but that they are either:

uncommon tasks (e.g. usually only done one time when setting up a new Linux machine),
too complex for my cheatsheet format, or
some combination of the above.

Setting a static IP address

We assume that:

you are running a Debian system.

Run this first to check your interfaces:

ip a

Let’s suppose you want interface eth0 to be assigned a static IP address.

Open the interfaces file in a text editor:

vi /etc/network/interfaces

You probably already see a line like:

iface eth0 inet dhcp

Let’s suppose you want to assign 192.168.0.2/24 as your interface address, and `192.168.0.1 as the default gateway.

Replace only that one line with:

auto eth0
iface eth0 inet static
    address 192.168.0.2/24
    gateway 192.168.0.1

And restart the networking service:

sudo systemctl restart networking

(If you’re connected via. SSH, the window probably just froze for you. Just reconnect back with the new IP address.)

Useful reference:

Debian Wiki: NetworkConfiguration

Setting up a basic SSH server

We assume that you want:

to only allow public key authentication (and disallow password login).

We assume that:

you are running a Debian system, and
you have a client with a keypair ready to connect via. SSH.

The examples below will use the following dummy values:

Server host: 192.168.0.2
Server username: simshadows

I recommend an initial audit on the server from another computer on the network:

# Quickly scan common ports on your server
sudo nmap -sT -Pn 192.168.0.2
# The SSH port is `22/tcp`.

# Attempt to connect with an SSH client
ssh [email protected]
# You obviously won't be able to connect if the SSH server isn't running.

Run these commands

# Install the server
apt install openssh-server

# Double-check that the daemon is running
systemctl | grep ssh
# You should see `ssh.service` and `loaded active running`.

# Double-check open TCP ports
ss -tuln
# You should see `0.0.0.0:22` currently in the `LISTEN` state.

I recommend running the audit again to check that the port is open, accessible, and ssh can connect.

You should also notice that login is possible via. password input.

Add your keys to the server now as needed (to prevent locking yourself out):

ssh-copy-id [email protected]

Create this file to configure auth restriction to public key only:

/etc/ssh/sshd_config.d/20-force_publickey_auth.conf

PasswordAuthentication no
AuthenticationMethods publickey

Restart the daemon:

sudo systemctl restart ssh.service

I recommend attempting to authenticate via. a machine that does not have a public key to ensure that we now prevent password authentication.

Useful references for further configuration: