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Minimal Debian

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Debian Vader

Debian 9 “Stretch” is the latest stable release of the popular Linux operating system. I use Debian’s network installer image to create a console-only base configuration that can be customized for various tasks and alternate desktops. 1

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 stretch), testing (buster), and unstable (sid).

Below is a visual walk-through of a sample workstation setup that makes use of the entire disk divided into 2 partitions: a boot partition, 2 and an encrypted partition used by the Logical Volume Manager (LVM) to create “virtual partitions” (Logical Volumes). Installing LVM on top of the encrypted partition allows:

  • creation of multiple LVs protected by a single passphrase entered at boot time
  • dynamic resizing of filesystems (set aside unallocated space and make use of it as needed)
  • snapshots of filesystems that can be used as backups or to restore a previous state 3

0. Prepare install media

Download and verify the (unofficial with firmware) 64-bit firmware-9.4.0-amd64-netinst.iso

$ wget -c https://cdimage.debian.org/cdimage/unofficial/non-free/cd-including-firmware/current/amd64/iso-cd/firmware-9.4.0-amd64-netinst.iso
$ wget -c https://cdimage.debian.org/cdimage/unofficial/non-free/cd-including-firmware/current/amd64/iso-cd/SHA256SUMS
$ sha256sum -c SHA256SUMS
firmware-9.4.0-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 the device using …

$ sudo dd if=firmware-9.4.0-amd64-netinst.iso of=/dev/sde bs=4M && sudo sync

Minimal installer (requires network connection) downloads all the latest packages during setup. 4

1. 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

2. Partitions

Sample layout:

  • sda1 is a 512MB boot partition
  • sda2 uses remaining storage as a LUKS encrypted partition
  • LVM installed on encrypted partition; contains volume group with 3 logical volumes: root + swap + home

Partitioning method

Partition disks

Partition table

Free space

New partition

Partition size

Primary partition

Beginning

Modify the default mount options …

Mount point: /boot
Bootable flag: on

Mount point

Boot

Bootable flag

Done

Assign the remaining storage to the encrypted partition …

Free space

New partition

Partition size

Primary partition

Modify default mount options …

Use as: physical volume for encryption
Erase data: no

If the hard disk has not been securely wiped prior to installing Debian you may want to configure Erase data: yes. Note, however, depending on the size of the disk this operation can last several hours.

Use as

Physical volume for encryption

Erase data

Done

Configure encrypted volumes

Write changes

Create encrypted

Devices to encrypt

Finish

Passphrase

Verify passphrase

Select encrypted volume and modify default mount options …

Use as: physical volume for LVM

Select

Use as

Physical volume for LVM

Done

Create a LVM volume group with 3 logical volumes …

Configure LVM

Write changes

Create volume group

Vg name

Device for vg

Create lv

Vg

Lv root

Lv root size

Create lv

Vg

Lv swap

Lv swap size

Create lv

Vg

Lv home

Set aside some unused space for future requirements. LVM makes it easy to expand or create new filesystems as needed …

Lv home size

Finish lvm

Select LV root and modify default mount options …

Use as: Ext4
Mount point: /

Select lv root

Use as

Ext4

Mount point

Root

Done

Select LV swap and modify default mount options …

Use as: swap area

Select lv swap

Use as

Swap

Done

Select LV home and modify default mount options … 5

Use as: Ext4
Mount point: /home
Reserved blocks: 1%

Select lv home

Use as

Ext4

Mount point

Home

Reserved blocks

Percent

Done

Write changes to disk …

Finish partitioning

Write changes

Installing

3. Install packages and finish up

Scan

Archive mirror

Use the Debian global mirrors service deb.debian.org

Mirror hostname

Mirror directory

Proxy

Pakage survey

Select only [*] standard system utilities and leave the remaining tasks 6 unmarked …

Software selection

Packages are downloaded and the installer makes its finishing touches …

Install GRUB to MBR

GRUB device

Finish

4. First boot

GRUB menu

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

Unlock passphrase

Login

Login and run timedatectl to confirm system date+time is properly configured …

timedatectl

5. Network

Check which network interfaces are detected and settings …

ip a

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. 7 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.

Create a temporary wireless interface connection to WPA2 encrypted access points manually using wpa_supplicant + wpa_passphrase + dhclinet. Sample setup of wlp1s0 (as root) …

ip link set wlp1s0 up             ## bring up interface
iw dev wlp1s0 link                ## get link status
iw dev wlp1s0 scan | grep SSID    ## scan for access points
wpa_supplicant -i wlp1s0 -c<(wpa_passphrase "MY_SSID" "MY_PASSPHRASE")   ## connect to WPA/WPA2 ... add '-B' to background process
dhclient wlp1s0                   ## obtain IP address

More permanent configurations may be set in interfaces. Sample setup 8 with a static IP address …

iface wlp1s0 inet static
address 192.168.1.77
netmask 255.255.255.0
gateway 192.168.1.1                                                              
wpa-ssid MY_SSID
wpa-psk MY_PASSPHRASE
dns-nameservers 8.8.8.8 8.8.4.4                                                  

Alternative setup using DHCP …

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

Once a link is established install an (optional) 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.

6. Upgrade

Install any upgrades …

apt update; apt full-upgrade

7. Secure access using SSH keys

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

8. 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 stretch-backports install PACKAGE

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

# Base repository
deb http://deb.debian.org/debian/ stretch main contrib non-free
deb-src http://deb.debian.org/debian/ stretch main contrib non-free

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

# Stable updates
deb http://deb.debian.org/debian stretch-updates main contrib non-free
deb-src http://deb.debian.org/debian stretch-updates main contrib non-free

# Stable backports
deb http://deb.debian.org/debian stretch-backports main contrib non-free
deb-src http://deb.debian.org/debian stretch-backports main contrib non-free

Any time sources.list is modified be sure to update the package database …

apt update

9. Automatic security updates

Fetch and install the latest fixes courtesy of unattended upgrades. Useful feature for a home server; on the desktop I manage updates myself.

10. Sudo

Install sudo to temporarily provide your USER (example: foo) account with root privileges …

apt install sudo
adduser foo sudo

To allow foo to shutdown or reboot the system, first create the file /etc/sudoers.d/00-alias containing …

# Cmnd alias specification
Cmnd_Alias SHUTDOWN_CMDS = /sbin/poweroff, /sbin/reboot, /sbin/shutdown

Starting with Stretch, if you run as USER the command dmesg to read the contents of the kernel message buffer you will see …

dmesg: read kernel buffer failed: Operation not permitted

Turns out it is a (security) feature not a bug!

To allow foo to read the kernel log without being prompted for a password - and use our newly-created Cmnd_Alias SHUTDOWN_CMDS - create the file /etc/sudoers.d/01-nopasswd containg the NOPASSWD option …

# Allow specified users to execute these commands without password
foo ALL=(ALL) NOPASSWD: SHUTDOWN_CMDS, /bin/dmesg

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

alias dmesg='sudo dmesg'
alias poweroff='sudo /sbin/poweroff'
alias reboot='sudo /sbin/reboot'
alias shutdown='sudo /sbin/shutdown'

11. SSD

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

cp /usr/share/doc/util-linux/examples/fstrim.{service,timer} /etc/systemd/system/
systemctl enable fstrim.timer

12. Where to go next …

… is up to YOU. I created a post-install setup script that builds on a minimal install towards a more complete console setup, and can also install the i3 tiling window manager plus a packages collection suitable for a workstation.

Happy hacking!

Notes


  1. Image courtesy of jschild. [return]
  2. Note that encrypted root requires an unencrypted boot. [return]
  3. Very helpful! LVM post on the Arch Wiki. [return]
  4. An alternative is adding the image to a USB stick with multiple Linux installers. [return]
  5. 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 the default 5% reserve set aside by Debian to 1%. [return]
  6. Task selection menu can be used post-install by running (as root) tasksel. [return]
  7. 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. [return]
  8. 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. [return]