Minimal Debian

Last updated on 2021-03-28 • Tagged under  # debian  # linux  # crypt

Debian 10 aka "buster" is the latest stable release of the popular Linux operating system. I use Debian's (unofficial) network installer image (which includes non-free firmware for pesky wifi cards) to create a minimal, console-only base configuration that can be customized for various tasks and desktops.

Let's go!

Debian GNU/Linux is an operating system created by volunteers of one of the largest and longest-running free software projects in the world. There are 3 release branches: stable (code-named "buster"), testing ("bullseye"), and unstable ("sid").

Below is a visual walk-through of an installation that makes use of the entire disk divided into two partitions: a small boot partition, with the remaining storage dedicated to a Linux Unified Key Setup (LUKS) encrypted partition used by the Logical Volume Manager (LVM) to create “virtual partitions” (Logical Volumes or LVs) for separate root and home.

Installing LVM on top of the encrypted partition allows:

• creation of multiple LVs protected by a single passphrase
• dynamic resizing of LVs as needed
• snapshots of LVs that can be used as backups or to restore a previous state

Sample device uses BIOS MBR and boots in legacy boot mode. Search online about extrapolating from these steps to deal with /boot/efi. Avail yourself of Debian's guided partitioning option, as I do below, and all the necessary arrangements are auto-configured for you.

Prepare install media

Download and verify firmware-10.9.0-amd64-netinst.iso ...

$ wget -c https://cdimage.debian.org/cdimage/unofficial/non-free/cd-including-firmware/current/amd64/iso-cd/firmware-10.9.0-amd64-netinst.iso
$ wget https://cdimage.debian.org/cdimage/unofficial/non-free/cd-including-firmware/current/amd64/iso-cd/SHA256SUMS
$ sha256sum -c --ignore-missing SHA256SUMS
firmware-10.9.0-amd64-netinst.iso: OK

Write the installer to an unmounted USB storage device using dd as root. BE VERY CAREFUL TO NOTE THE PROPER DEVICE. ALL DATA ON THE DEVICE WILL BE OVERWRITTEN.

Example: On a Linux system, if a USB stick appears as sde1, then write the installer to sde (no partition number) using ...

$ sudo dd if=path/to/firmware-10.9.0-amd64-netinst.iso of=/dev/sde bs=4M status=progress oflag=sync

Launch

Partitions

Select the guided partitioning option to make use of the entire disk configured with LVM on LUKS. I also recommend creating a separate /home. By default, this creates:

• a small, unencrypted boot
• remaining storage dedicated to a LUKS-encrypted partition with LVM
• logical volumes created for root, swap, and home

Settings can be altered (alternate filesystems, mount options, etc) before writing the partition layout to disk. ¹ If finer-grained control is desired, select manual partitioning.

Install packages and finish up

Use the Debian global mirrors service deb.debian.org ...

Select only [*] standard system utilities and leave the remaining tasks ² unmarked ...

Packages are downloaded and the installer makes its finishing touches ...

First boot

GRUB menu ...

User is prompted for the passphrase to unlock the encrypted partition ...

Login and welcome to Debian!

Network

Check which network interfaces are detected and settings ...

$ ip link

Wired interfaces are usually auto-configured by default and assigned an IP address courtesy of DHCP.

To assign a static address, deactivate the wired interface and create a new entry in /etc/network/interfaces. ³ Sample entry for enp3s0 ...

# The primary network interface
auto enp3s0
iface enp3s0 inet static
address 192.168.1.88
netmask 255.255.255.0
gateway 192.168.1.1
dns-nameservers 8.8.8.8 8.8.4.4

Bring up|down interface with if{up,down} enp3s0.

To create a wireless interface connection to WPA2-encrypted access points ⁴ using DHCP ...

iface wlp1s0 inet dhcp
wpa-ssid MY_SSID
wpa-psk MY_PASSPHRASE                                       
dns-nameservers 8.8.8.8 8.8.4.4

Optional: Once a link is established, install a network manager utility. Packages network-manager and network-manager-gnome provide the console nmcli and graphical nm-applet clients respectively . Comment out (deactivate) any entries in interfaces that will be managed by network-manager.

Upgrade

Install any upgrades ...

# apt update && apt full-upgrade

Keyboard

If you desire a different default language/keymap, either modify /etc/default/keyboard or run ...

# dpkg-reconfigure keyboard-configuration

Console fonts

Discover available fonts in /usr/share/consolefonts. Set and display a font (example: Lat15-Terminus20x10) for the current session ...

# setfont Lat15-Terminus20x10
# showconsolefont

To make the selection persistent, either modify /etc/default/console-setup or run ...

# dpkg-reconfigure console-setup

Sudo

Install sudo to temporarily provide your non-root user (example: foo) account with root privileges ...

# apt install sudo && adduser foo sudo

To allow foo to suspend, shutdown or reboot the system without being prompted for a password, first create the file /etc/sudoers.d/00-alias containing ...

User_Alias ADMIN = foo
Cmnd_Alias SYS_CMDS = /usr/bin/systemctl poweroff, /usr/bin/systemctl reboot, /usr/bin/systemctl suspend

... and then create the file /etc/sudoers.d/01-nopasswd containing the NOPASSWD option ...

# allow specified users to execute these commands without password
ADMIN ALL=(ALL) NOPASSWD: SYS_CMDS

I add aliases for the commands in my ~/.bashrc to auto-include sudo ...

alias bye='sudo /usr/bin/systemctl poweroff'
alias reboot='sudo /usr/bin/systemctl reboot'
alias zzz='sudo /usr/bin/systemctl suspend'

Sysctl

If a non-root user runs dmesg to read the contents of the kernel message buffer they will see ...

dmesg: read kernel buffer failed: Operation not permitted

Turns out it is a security feature not a bug!

To allow users to read the kernel log without being prompted for a password, modify /etc/sysctl.conf by adding ...

kernel.dmesg_restrict = 0

... and reload the configuration ...

$ sudo sysctl -p

Main, non-free, contrib, and backports

Debian uses three archives to distinguish between software packages based on their licenses. Main is enabled by default and includes everything that satisfies the conditions of the Debian Free Software Guidelines. Non-free contains packages that do not meet all the conditions of the DFSG but can be freely distributed, and contrib packages are open-source themselves but rely on software in non-free to work.

Backports contains packages drawn from the testing (and sometimes unstable) archive and modified to work in the current stable release. All backports are disabled by default (to prevent unintended system upgrades) and are installed on a per PACKAGE basis by running ...

# apt -t buster-backports install PACKAGE

Modify /etc/apt/sources.list to add contrib, non-free, and backports ...

# Base repository
deb https://deb.debian.org/debian/ buster main contrib non-free
deb-src https://deb.debian.org/debian/ buster main contrib non-free

# Security updates
deb https://security.debian.org/debian-security buster/updates main contrib non-free
deb-src https://security.debian.org/debian-security buster/updates main contrib non-free

# Stable updates
deb https://deb.debian.org/debian buster-updates main contrib non-free
deb-src https://deb.debian.org/debian buster-updates main contrib non-free

# Stable backports
deb https://deb.debian.org/debian buster-backports main contrib non-free
deb-src https://deb.debian.org/debian buster-backports main contrib non-free

Any time sources.list is modified its necessary to update the package database ...

$ sudo apt update

I add the alias aaa to my ~/.bashrc that combines, in a single command:

• updating the package database
• running a full upgrade
• removing package files that can no longer be downloaded, and are largely useless
• prompting to remove packages automatically installed to satisfy dependencies for other packages and are now no longer needed

Add ...

alias aaa="sudo apt update && apt list --upgradable && sudo apt full-upgrade && sudo apt autoclean && sudo apt autoremove"

Reload the new settings, and run ...

$ source ~/.bashrc
$ aaa

Command not found

Automatically search the official repositories when entering an unrecognized command, courtesy of the command-not-found package ...

$ sudo apt install command-not-found apt-file
$ sudo apt-file update && sudo update-command-not-found

Re-login to activate.

Swapfile

In lieu of a dedicated swap partition, an alternative is to create a swapfile. Example: A 2G /swapfile ...

$ sudo dd if=/dev/zero of=/swapfile bs=1M count=2048 status=progress

Only root should be granted read/write access ...

$ sudo chmod 600 /swapfile

Create the swap area and activate ...

$ sudo mkswap /swapfile
$ sudo swapon /swapfile && free -h

Make the change permanent by adding to /etc/fstab ...

/swapfile none swap sw 0 0

SSD

Periodic TRIM optimizes performance on SSD storage. Enable a weekly task that discards unused blocks on the drive ...

$ sudo systemctl enable fstrim.timer

mlocate

Setup the locate command and database for finding files ...

$ sudo apt install mlocate && sudo /etc/cron.daily/mlocate

Dot bashrc

Modify ~/.bashrc and create a colourful custom prompt ...

# colour codes
GREEN="\\[\\e[1;32m\\]"
YELLOW="\\[\\e[1;33m\\]"
BLUE="\\[\\e[1;34m\\]"
MAGENTA="\\[\\e[1;35m\\]"
WHITE="\\[\\e[1;37m\\]"
RESET="\\[\\e[0m\\]"

# Set a two-line prompt. If accessing via ssh include 'ssh-session' message.
if [[ -n "$SSH_CLIENT" ]]; then
    ssh_message="-ssh_session"
fi
PS1="${MAGENTA}\\u ${WHITE}at ${GREEN}\\h${YELLOW}${ssh_message} ${WHITE}in ${BLUE}\\w \\n$WHITE\$${RESET} "

Add aliases and functions, enable unlimited history, and more. Example: my .bashrc.

Microcode

Intel and AMD processors may periodically need updates to their microcode firmware. Microcode can be updated (and kept in volatile memory) during boot by installing either intel-microcode or amd64-microcode (AMD) ...

$ sudo apt install intel-microcode

Sample output from my laptop before reboot ...

$ dmesg | grep microcode
[    0.042819] [Firmware Bug]: TSC_DEADLINE disabled due to Errata; please update microcode to version: 0x20 (or later)
[    1.325081] microcode: sig=0x40651, pf=0x40, revision=0x15
[    1.325137] microcode: Microcode Update Driver: v2.2.
$ grep microcode /proc/cpuinfo 
microcode	: 0x15
microcode	: 0x15

... and after reboot ...

$ dmesg | grep microcode
[    0.000000] microcode: microcode updated early to revision 0x24, date = 2018-04-02
[    1.329836] microcode: sig=0x40651, pf=0x40, revision=0x24
[    1.329903] microcode: Microcode Update Driver: v2.2.
$ grep microcode /proc/cpuinfo 
microcode	: 0x24
microcode	: 0x24

Link: Microcode

Secure access using SSH keys

Create cryptographic keys, install the OpenSSH server, and configure remote access.

Helpful

• The Debian Administrator's Handbook
  • In-depth guide to becoming a Debian power-user/sysadmin. Read online or download the ebook.
• Debian Package Tracker
  • A searchable interface that packs a lot of information about a given package on a single page.
• r/debian
  • Reddit forum for Debian.
• The Linux Command Line
  • Command line use, programs, and shell scripting. Free ebook download.
• ArchWiki
  • Dedicated to Arch Linux, but contains many excellent HOWTOs relevant to all Linux distros.

Where to go next ...

... is up to YOU. I use Ansible to setup my own Debian machines, usually with Openbox. It might give you some ideas.

Happy hacking!

• GPL-2.0+ image of “bestFriend” courtesy of Alex Makas.

Notes

» Later: Put a modem-router in bridge mode

« Earlier: Automatic security and other upgrades in Debian