Debian amdin cheat sheet¶

1. Network setup¶

If you have a dhcp server, it will distriubt you an IP address. But sometimes, you don't have a dhcp server. So you need to setup a static IP address.

1.1 Get available network interfaces¶

# show all activated interfaces
ip a

# show all interfaces, can be up or down 
ip -c link

1.2 Configure static IP (tested on debian 10/11)¶

The main config of network interfaces are located at /etc/network/interfaces

suod vim /etc/network/interfaces

You should see below text. In this example, the name of the interface is eth0 and it uses dhcp

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

source /etc/network/interfaces.d/*

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
allow-hotplug eth0
iface eth0 inet dhcp

Change it from dhcp to static. You need to add all the required informaton for the ip address to work.

Below is an example: (ip: 10.50.5.58, mask: 255.255.255.0, gateway: 10.50.0.1, dns:10.50.0.10)

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

source /etc/network/interfaces.d/*

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
allow-hotplug eth0
iface eth0 inet static
        address 10.50.5.58/24
        gateway 10.50.0.1
        # dns-* options are implemented by the resolvconf package, if installed
        dns-nameservers 10.50.0.10 8.8.8.8
        dns-search casd.eu casd.local

Note, you need to restart the service to activate the new configuration

systemctl restart networking.service; ifup eth0

1.3 DNS configuration¶

The dns configuration is located at /etc/resolv.conf. Below is an example

search casd.local
nameserver 10.50.0.10
nameserver 8.8.8.8

Normally, you don't need to edit this file directly. Debian provides two packages(openresolv and resolvconf), each of which contains a program named resolvconf, which may be used to control (or outright prevent) the alteration of the /etc/resolv.conf file by various networking programs. They conflict with each other, so you have to pick at most one of them.

So if you modified the /etc/network/interfaces and restart network.service, the program ((openresolv or resolvconf)) will update the /etc/resolv.conf.

You can view it to see exactly which dns you are using.

2. Apt configuration¶

If your apt can't find any package, it means your repo is not pointing at the right server url. You need to edit /etc/apt/sources.list, and add appropriate repo url. Below is the minimun setup for apt to work.

deb http://deb.debian.org/debian/ bullseye main
deb-src http://deb.debian.org/debian/ bullseye main
deb http://security.debian.org/debian-security bullseye-security main contrib
deb-src http://security.debian.org/debian-security bullseye-security main contrib
deb http://deb.debian.org/debian/ bullseye-updates main contrib
deb-src http://deb.debian.org/debian/ bullseye-updates main contrib

3. Security¶

Add user to sudoer list¶

Solution1: The easiest way is to add user to the sudoer group

# loign as root, because usermod file is in /usr/sbin
su -

# add user to the sudoer group
usermod -aG sudo user fbar

# To ensure that the user has been added to the group
sudo whoami

Solution2: You can also edit the /etc/sudoers (always use visudo)

visudo

# in the file /etc/sudoers, add the following line
username  ALL=(ALL) NOPASSWD:ALL

# save and quit the visudo editor

Note the user need to logout and re login to have the sudo group.

Add trusted root ca¶

https://www.digitalocean.com/community/tutorials/how-to-set-up-and-configure-a-certificate-authority-ca-on-debian-11

sudo cp /tmp/ca.crt /usr/local/share/ca-certificates/
sudo update-ca-certificates

# you can force the refresh of the trusted ca store