General Linux

Installing a software RAID 10 Debian system with LUKS disk encryption

In this guide we will be installing Debian 9 (aka stretch) on a physical server with 4 disks. The role of this machice is to be used as a Storage/NAS system. We will create a software RAID 10 setup, with LVM and LUKS full disk encryption. Our goals:

  • Install a Debian 9 with RAID10/LVM/LUKS.
  • Secure SSH.
  • Enable Firewall (UFW).
  • Setup bonding with the two network cards.
  • Setup remote system unlock with dropbear and initramfs.
  • Setup disk-monitoring with smartmontools and mdadm.
  • Setup kexec for faster reboots.

Computer specs

  • Type: HP ProLiant MicroServer
  • CPU: AMD Turion(tm) II Neo N40L Dual-Core Processor
  • RAM: 2GB
  • Disks: 4x3TB SATA
  • Network:
    • Broadcom Limited NetXtreme BCM5723 Gigabit Ethernet PCIe (on board)
    • Intel Corporation 82574L Gigabit Network Connection (extra)


  • Server IP:
  • Netmask:
  • Gateway IP:
  • DNS IP:
  • Hostname:

Install Debian stretch

Basic Settings

It would probably be more clear if there were screenshots for each step, but this was an installation on a physical server and taking photos for each step, opposes my laziness :). Just follow the instructions and you will be fine.

  • Choose: Install
  • Language: English
  • Country: other
  • Europe: Cyprus
  • Country to base default locale settings: United States
  • Keymap to use: American English
  • Primary network interface: enp3s0: Broadcom Limeted NetXtream BCM5723 Gigabit Ethernet PCIe
  • Let it get an IP from DHCP
  • Hostname: storage
  • Domain name:
  • Root password: SomethingBigAndUnpredictable
  • Re-enter password to verify: SomethingBigAndUnpredictable
  • Full name: Sysadmin
  • Username: admin
  • Choose a password for the new user: AlsoSomethingBigAndUnpredictable
  • Re-enter password to verify: AlsoSomethingBigAndUnpredictable
  • Select your time zone: Asia/Nicosia
  • Partitioning method: Manual

Feel free to adjust the above according to your own preferences.


There are 4 disks of 3TB each (3.0 TB SATA):

  • SCSI1 (0,0,0) (sda)
  • SCSI2 (0,0,0) (sdb)
  • SCSI3 (0,0,0) (sdc)
  • SCSI4 (0,0,0) (sdd)

Not really SCSI but SATA in fact.

Partition the devices

Then create a raid partition for /boot:

  • Select the free space of sda and ‘Enter’
  • Create a new partition
  • New partition size: 512 MB
  • Location of new partition: Beginning
  • Use as: physical volume for RAID
  • Done setting up the partition

Lastly create the raid partition to be used by the encrypted volume:

  • Select the free space of sda and ‘Enter’
  • Create a new partition
  • New partition size: 3.0 TB
  • Location of new partition: Beginning
  • Use as: physical volume for RAID
  • Done setting up the partition

Repeat the above steps for sdb, sdc and sdd.

Setup Software RAID 10

First select ‘Configure software RAID’ and follow these steps:

  • Write the changes to the storage devices and configure RAID? Yes

The we create the software RAID (MD) devices. First we create device md0 for /boot:

  • Create MD Device
  • RAID10
  • Number of active devices inn the RAID10 array: 4
  • Number of spare devices inn the RAID10 array: 0
  • Active devices for the RAID10 array (use ‘Space bar’ to select)
    • /dev/sda2
    • /dev/sdb2
    • /dev/sdc2
    • /dev/sdd2
  • Press ‘Continue’ when done.

Then we create the software RAID device to be used for the encrypted volume (md1):

  • Create MD Device
  • RAID10
  • Number of active devices inn the RAID10 array: 4
  • Number of spare devices inn the RAID10 array: 0
  • Active devices for the RAID10 array (use the ‘Space bar’ to select)
    • /dev/sda3
    • /dev/sdb3
    • /dev/sdc3
    • /dev/sdd3
  • Press ‘Continue’ when done.
  • Press ‘Finish’ when done.

Create the /boot volume

When done press ‘Finish partitioning and write changes to disk’.`

When finished you will see a ‘RAID10 device #0 1GB Software RAID device’:

  • Select: #1 1.0GB
  • Use as: Ext4 journaling file system
  • Mount point: /boot
  • Done setting up the partition

Setup the encrypted volume

We will be using the software RAID /dev/md1 device for the encrypted volume.

Now select ‘Configure encrypted volumes’ and follow these steps:

  • Write the changes to disk and configure encrypted volumes? Yes
  • Create encrypted volumes

  • Select: /dev/md1
  • Erase data: yes (this will take a long time)
  • Done setting up the partition

  • Write the changes to disk and configure encrypted volumes? Yes

  • Finish
  • Encryption passphrase: MyVeryLongEncryptionPassphrase
  • Re-enter the passphrase to verify: MyVeryLongEncryptionPassphrase
  • Setup LVM

    Next we select the ‘Configure the Logical Volume Manager’ option and follow these steps:

    • Write the changes to disks and configure LVM? Yes
  • Create volume group

  • Volume group name: VG00
  • Devices for the new volume group:
    • /dev/mapper/md1_crypt
  • Then we create the Logical Volumes (LV). First let’s create a SWAP volume:

    • Create logical volume
    • Volume group: VG00
    • Logical volume name: SWAP
    • Logical volume size: 2048MB (2G is more than enough for this system)

    Lastly we create the system (ROOT) volume. On an enterprise installation we may want to use different volumes for /usr, /home, /var, etc but for a home installation we will be fine to use just one.

    • Create logical volume
    • Volume group: VG00
    • Logical volume name: ROOT
    • Logical volume size: 5996818MB (All available space)

    Press ‘Finish’ when done.

    Start the installation

    After all the steps are completed these Logical Volumes will be present on the system:

    • LVM VG VG00, LV ROOT 0 6.0 TB
    • LVM VG VG00, LV SWAP 0 2.0 GB

    Create the ROOT filesystem

    Under the ‘LVM VG VG00, LV ROOT 0 6.0 TB’ line select the ‘#1 6.0TB’ option:

    • Use as: Ext4 journaling file system
    • Mount point: /
    • Done setting up this partition

    Create the SWAP space

    Under the ‘LVM VG VG00, LV SWAP 0 2.0 GB’ line select the ‘#1 2.0GB’ option:

    • Use as: swap area
    • Done setting up this partition

    Now we are ready to write the changes and start the installation. Press the ‘Finish partitioning and write changes to disk’ option to continue:

    • Write the changes to disks? Yes

    Wait for the base install to finish. Then select a country close to you. No debian mirrors in Cyprus so I use UK:

    • Debian archive mirror country: United Kingdom
    • Debian archive mirror:
    • HTTP proxy: (none)

    Wait for the APT configuration to Finish.

    • Participate in the package usage survey: no
  • Choose software to install:

    • SSH server
    • standard system utilities
  • Wait while software is installing

    • Install the GRUB boot loader to the master boot record.
    • Device for boot loader installation:
      • /dev/sda

    Wait for the installation to finish and reboot. Remember to remove the USB during the reboot cycle.

    Post install steps

    During start-up you will see the ‘Please unlock md1_crypt’ prompt. Type your LUKS passphrase to unlock the disk and continue.

    Update and Upgrade

    Login as root:

    # apt update && apt -y dist-upgrade

    Install essential packages

    # apt -y install vim htop multitail ntp byobu ufw unattended-upgrades downtimed

    Secure ssh

    You need to generate an SSH key pair on you PC, if you don’t have one (you should!):

    $ ssh-keygen -b 4096

    Copy the public key:

    $ cat ~/.ssh/

    Paste the public key at the end of the /root/.ssh/authorized_keys file in your server and try to login from your PC:

    $ ssh root@

    Some final adjustments on your SSH config (/etc/ssh/sshd_config). Change these values:

    Port 2233
    PasswordAuthentication no

    Restart SSH:

    # systemctl restart ssh.service

    Enable the UFW firewall

    We are using port 2233 for SSH so we need to allow that and enable the firewall:

    # ufw allow 2233/tcp
    # ufw enable

    Setup bonding

    Since we have two ethernet cards, we may take advantage of thr Linux bonding feature and join them as one. We will be using the Adaptive load balancing mode which provides load balancing of transmit, load balancing of receive for IPv4 and requires no configuration from the switch side.

    First we need to install ifenslave:

    # apt -y install ifenslave

    Set up this in /etc/network/interfaces:

    # 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
    # enp2s0 is manually configured, and slave to the "bond0" bonded NIC
    auto enp2s0
    iface eth0 inet manual
        bond-master bond0
    # enp3s01 is also manually configured, thus creating a 2-link bond.
    auto enp3s0
    iface eth1 inet manual
        bond-master bond0
    # bond0 is the bonded NIC and can be used like any other normal NIC.
    # bond0 is configured using static network information.
    auto bond0
    iface bond0 inet static
        # bond0 uses adaptive load balancing
        bond-mode 6
        bond-miimon 100
        bond-slaves enp2s0 enp3s0

    An ifup bond0 should bring the bonded interface up. Or you can just reboot.

    Setup remote-unlock with dropbear

    The server will be a headless system, located in a difficult to access location. So we need a way to unlock it when a power failure occurs. The most convenient way to do this is to use a mandos server but convenience comes at a cost. A safer and easier way is to use dropbear during boot (initrd). The weak point of this solution is that the server will be basically offline until the sysadmin manually unlocks it, to boot.

    First we install dropbear for initrd:

    # apt -y install dropbear-initramfs

    Then we set a custom ssh port for dropbear. This better be different than the custom ssh port we used earlier. Change the dropbear port to 2244 in /etc/dropbear-initramfs/config:

    DROPBEAR_OPTIONS="-p 2244"

    Add the static IP in the initramtools configuration (/etc/initramfs-tools/initramfs.conf):


    Copy the authorized_keys file in /etc/dropbear-initramfs:

    # cp /root/.ssh/authorized_keys /etc/dropbear-initramfs/

    Regenerate the initrd file:

    # update-initramfs -u

    Now reboot and ssh to it to test it:

    $ ssh -p 2244 root@

    If your pubkeys are in place you will enter a busybox shell. Enter the crypt-unlock command, supply your unlock passphrase and the system will boot to the encrypted system.

    Setup a local MTA for notifications

    We will be using our main mailserver as a smarthost for mail to go through.

    Install the postfix MTA and the mail utility:

    # apt -y install postfix mailutils

    Answer these questions:

    • General type of mail configuration: Internet with smarthost
    • System mail name:
    • SMTP relay host (blank for none):

    Test it:

    # echo 'Testing #1' | mail -s 'Test #1'

    If you get a mail in your mailbox then everything is set. If not extra configuration may be needed on the smarthost. Contact the sysadmin of the smarthost, or check the logs if you access to it.

    Setup pro-active disk monitoring

    Install smartmontools:

    # apt -y install smartmontools

    Enable S.M.A.R.T, offline testing, attribute autosave, short and long test on all 4 devices. Add these lines in /etc/smartd.conf:

    /dev/sda -a -d sat -o on -S on -s (S/../.././02|L/../../6/03) -m -M exec /usr/share/smartmontools/smartd-runner
    /dev/sdb -a -d sat -o on -S on -s (S/../.././02|L/../../6/03) -m -M exec /usr/share/smartmontools/smartd-runner
    /dev/sdc -a -d sat -o on -S on -s (S/../.././02|L/../../6/03) -m -M exec /usr/share/smartmontools/smartd-runner
    /dev/sdd -a -d sat -o on -S on -s (S/../.././02|L/../../6/03) -m -M exec /usr/share/smartmontools/smartd-runner

    Restart smartmontools:

    # systemctl restart smartmontools.service

    Setup Software RAID10 monitoring

    We also need to setup monitoring for the software raid. Add your email address in the /etc/mdadm/mdadm.conf file:


    Restart the mdmonitor service:

    # systemctl restart mdmonitor.service

    Setup kexec for faster reboots

    Kexec is a Linux kernel mechanism that can load a fresh kernel from a running system. This results in a “reboot” without in fact rebooting the computer. The system loads a new kernel, the system appears “rebooted” but skipping the BIOS?UEFI initialization, thus resulting in faster reboots.

    Install kexec-tools:

    # apt -y install kexec-tools

    The ‘Should kexec-tools handle reboots (sysvinit only)?’ question is related only to sysvinit systems. Since we are using systemd, it has no effect in our case.

    Now if you want to reboot instead of running reboot you can run systemctl kexec. The latter command will reboot the system without going though BIOS/UEFI, POST etc and your system downtime is minimized.

    And we are done! Store your server in a protected location, add a UPS for power backup and you are ready.



    How to remotely decrypt a LUKS encrypted Debian/Ubuntu System

    In this guide we will show how you can remotely decrypt a headless Debian or Ubuntu Linux system, that has been encrypted with LUKS.


    • A LUKS encrypted Debian jessie or Ubuntu xenial system
    • Keyboard and monitor for the initial system setup
    • Allow SSH root access on the decrypted system using public key authentication
    • Use a different port for ssh (assuming port 4422) on the decrypted system

      NOTE: using a different port than the standard SSH port (22) serves a double purpose. For once, you will not received the scary WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! message every time you will try to remotely unlock the system and as an additional bonus you will get less SSH attacks on the active system.

    Installing dropbear

    Dropbear is a lightweight SSH server especially suitable for initial ramdisk (initrd) environments and other lightweight systems.

    Install dropbear:

    # apt -y install dropbear

    Setup public key authentication for dropbear

    Create the homedir for the root user and the SSH configuration directory:

    # mkdir -p /etc/initramfs-tools/root/.ssh

    Append your client SSH pubkey to authorized_keys:

    # cat ~/.ssh/ | ssh -p 4422 root@encrypted-system "cat >> /etc/initramfs-tools/root/.ssh/authorized_keys"

    Setup a static IP for the unlock environment

    This step is optional but highly recommended if you are setting up a static, permanent service. If you skip this step DHCP will kick in, provided you have a DHCP Server in your environment.

    Run this command to update the /etc/initramfs-tools/initramfs.conf configuration file:

    echo IP= >> /etc/initramfs-tools/initramfs.conf

    Explanation of the different fields:

    NOTE: there are two successive colons (::) after the host_ip.

    Setup the unlock script

    Copy the following text in /etc/initramfs-tools/hooks/

    # By Stinky Parkia
    prereqs() {
        echo "$PREREQ"
    case "$1" in
        exit 0
    . "${CONFDIR}/initramfs.conf"
    . /usr/share/initramfs-tools/hook-functions
    if [ "${DROPBEAR}" != "n" ] && [ -r "/etc/crypttab" ] ; then
        cat > "${DESTDIR}/bin/unlock" < < EOF
    if PATH=/lib/unlock:/bin:/sbin /scripts/local-top/cryptroot; then
        kill \`ps | grep cryptroot | grep -v "grep" | awk '{print \$1}'\`
        # following line kill the remote shell right after the passphrase has
        # been entered.
        kill -9 \`ps | grep "\-sh" | grep -v "grep" | awk '{print \$1}'\`
        exit 0
    exit 1
        chmod 755 "${DESTDIR}/bin/unlock"
        mkdir -p "${DESTDIR}/lib/unlock"
        cat > "${DESTDIR}/lib/unlock/plymouth" < < EOF
    [ "\$1" == "--ping" ] && exit 1
    /bin/plymouth "\$@"
        chmod 755 "${DESTDIR}/lib/unlock/plymouth"
        echo To unlock root-partition run "unlock" >> ${DESTDIR}/etc/motd

    Make the script executable:

    # chmod +x /etc/initramfs-tools/hooks/

    Apply the configuration

    Apply the changes in the initial ramdisk:

    # update-initramfs -u

    Reboot the system:

    # reboot

    Remotely unlock the system

    From your client, SSH into the initial ramdisk:

    ssh root@encrypted-system 

    If everything is correct you will be greeted by this MOTD:

    To unlock root-partition run unlock
    BusyBox v1.22.1 (Ubuntu 1:1.22.0-15ubuntu1) built-in shell (ash)
    Enter 'help' for a list of built-in commands.

    Unlock the system and boot into it:

    # unlock
    Please unlock disk sda3_crypt: 

    You will get the following message and you will exit the remote shell if successful:

    cryptsetup: sda3_crypt set up successfully
    Connection to closed.

    You can now login to the active Linux system using the alternative port 4422:

    ssh -p 4422 root@encrypted-system

    If you can login successfully to your system you can remove the keyboard and monitor and hide your system somewhere where the Sun does not shine :).

    Thanks to Stinky Parkia for the excellent guide and the brilliant unlock script.