Minimal Debian

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

Debian buster bestFriend

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, and a second partition where all the remaining storage is encrypted using Linux Unified Key Setup (LUKS). Later, that encrypted storage is used by the Logical Volume Manager (LVM) to create “virtual partitions” (Logical Volumes or LVs) for separate root and home filesystems. Installing LVM on top of the encrypted partition allows the creation of multiple LVs protected by a single passphrase, and dynamic resizing of LVs as needed.

Sample configuration below uses BIOS MBR and boots in legacy boot mode. If using Debian's guided partitioning option, all the necessary partition arrangements are auto-configured whether the computer boots using MBR or UEFI.

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 the dd command 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) ...

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

Launch

Install

Select language

Select location

Configure keyboard

Detecting link

DHCP

Hostname

Domain

Root password

Verify password

Full name

Username

User password

Verify password

Select time zone

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 (plus a separate boot/efi partition if using UEFI to 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.

Partitioning method

Select disk

Separate home

Write changes

Erasing data

Passphrase

Re-enter passphrase

Amount to use

Finish partitioning

Write changes

Installing

Install packages and finish up

Install media

Archive mirror

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

Mirror hostname

Proxy

Retrieving files

Restart services

Package survey

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

Software selection

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

Install GRUB to MBR

GRUB device

Finish

First boot

GRUB menu ...

GRUB menu

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

Unlock passphrase

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 execute superuser commands without being prompted for a password, create the file /etc/sudoers.d/foo containing ...

foo ALL=(ALL) NOPASSWD: ALL

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.

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 for desktops, plus some favourite applications.

Happy hacking!

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

Notes

Reserved blocks can be used by privileged system processes to write to disk - useful if a full filesystem blocks users from writing - and reduce disk fragmentation. On large non-root partitions, extra space can be gained by reducing this reserve. Example: Highlight and select /home partition, select Reserved blocks: and reduce the default 5% reserve set aside by Debian to 1%.

Task selection menu can be used post-install by running the command tasksel.

Problem: Setting the network interface to static address can result in /etc/resolv.conf being overwritten every few minutes with an IPv6 address that breaks DNS. The "fix" is to maually set nameserver 8.8.8.8 in resolv.conf and install the resolvconf package. Note that dns-nameservers entries are ignored if resolvconf is not installed.

⁴

Multiple wireless static IP address setups can be created with iface wlp1s0_NAME inet static and [de]activated with if{up.down} wlp1s0=wlp1s0_NAME.

» Later: Put a modem-router in bridge mode

« Earlier: Automatic security and other upgrades in Debian