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debian.md

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title: Debian Server breadcrumbs:

  • title: Configuration
  • title: Linux Server --- {% include header.md %}

Using

{:.no_toc}

  • Debian 10 Buster

Basic Setup

Installation

  • Always verify the downloaded installation image after downloading it.
  • Use UEFI if possible.
  • Use the non-graphical installer. It's basically the same as the graphical one.
  • Localization:
    • Language: United States English.
    • Location: Your location.
    • Locale: United States UTF-8 (en_US.UTF-8).
    • Keymap: Your keyboard's keymap.
  • Use an FQDN as the hostname. It'll set both the shortname and the FQDN.
  • Use separate password for root and your personal admin user.
  • System disk partitioning:
    • (Recommended for "simple" systems) Manually partition: One partition using all space, mounted as EXT4 at /.
    • (Recommended for "complex" systems) Manually partition, see system storage.
    • Swap can be set up later as a file or LVM volume.
    • When using LVM: Create the partition for the volume group, configure LVM (separate menu), configure the LVM volumes (filesystem and mount).
  • At the software selection menu, select only "SSH server" and "standard system utilities".
  • If it asks to install non-free firmware, take note of the packages so they can be installed later.
  • Install GRUB to the used disk.

Reconfigure Clones

If you didn't already configure this during the installation. Typically the case if cloning a template VMs or something.

  1. Check the system status:
    • Check for failed services: systemctl --failed
    • Check that AppArmor is operational: apparmor_status
  2. Update the root password: passwd
  3. Localization:
    • Check current locale:
      • locale should return en_US.UTF-8.
      • Update if wrong: update-locale LANG=en_US.UTF-8
    • Check the keymap:
      • Try typing characters specific to your keyboard.
      • Update if wrong: dpkg-reconfigure keyboard-configuration
  4. Set the hostname:
    • Set the shortname: hostnamectl set-hostname <shortname>
    • Set both the shortname and FQDN in /etc/hosts using the following format: 127.0.0.1 <fqdn> <shortname>
    • Check the hostnames with hostname (shortname) and hostname --fqdn (FQDN).

Basic Configuration

  1. Packages:
    • (Optional) Enable the contrib and non-free repo areas by setting main contrib non-free for every deb/deb-src in /etc/apt/sources.list.
    • Update, upgrade and auto-remove.
    • Install basics: sudo ca-certificates
    • Install tools: tree vim screen curl net-tools netutils htop iotop irqtop nmap
    • (Optional) Install per-user tmpdirs: libpam-tmpdir
  2. (Optional) Update the default editor: update-alternatives --config editor
  3. Add mount options:
    • Setup hidepid:
      • Add PID monitor group: groupadd -g 1500 pidmonitor
      • Add your personal user to the PID monitor group: usermod -aG pidmonitor <user>
      • Enable hidepid in /etc/fstab: proc /proc proc defaults,hidepid=2,gid=1500 0 0
    • (Optional) Setup extra mount options: See Storage.
    • Run mount -a to validate fstab.
    • (Optional) Restart the system.
  4. Setup your personal user:
    • If it doesn't exist, create it: adduser <username>
    • Add the relevant groups (using usermod -aG <group> <user>):
      • sudo for sudo access.
      • systemd-journal for system log access.
      • pidmonitor (whatever it's called) if using hidepid, to see all processes.
    • Add your personal SSH pubkey to ~/.ssh/authorized_keys and fix the owner and permissions (700 for dir, 600 for file).
      • Hint: Get https://github.com/<user>.keys and filter the results.
    • Try logging in remotely and gain root access through sudo.

  5. Setup SSHD:

    • In /etc/ssh/sshd_config, set:

      PermitRootLogin no
PasswordAuthentication no
AllowTcpForwarding no
GatewayPorts no
#AcceptEnv ...

    • Restart sshd.

  6. Update MOTD:

    • Clear /etc/motd and /etc/issue.
    • (Optional) Add a MOTD script (see below).

  7. (Optional) Enable persistent logging:

    • In /etc/systemd/journald.conf, under [Journal], set Storage=persistent.
    • auto (the default) is like persistent, but does not automatically create the log directory.
    • The default journal directory is /var/log/journal.

Machine-Specific Configuration

Physical Host

  1. Install extra firmware:
    • Enable the non-free repo areas.
    • Install firmware-linux (or firmware-linux-free) for some common firmware and microcode.
    • APT package examples: firmware-atheros -bnx2 -bnx2x -ralink -realtek
    • If it asked to install non-free firmware in the initial installation installation, try to install it now.
    • Install firmware from other sources (e.g. for some Intel NICs).
    • Update microcode: Install intel-microcode (for Intel) or amd64-microcode (for AMD) and reboot (now or later).
  2. Install smartmontools and run smartctl -s on <dev> for all physical drives to enable SMART monitoring.
  3. Setup lm_sensors to monitor sensors:
    1. Install: apt install lm-sensors
    2. Run sensors to make sure it runs without errors.
    3. For further configuration (more sensors) and more info, see Linux Server Applications: lm_sensors.
  4. Mask ctrl-alt-del.target to disable CTRL+ALT+DEL reboot at the login screen.

QEMU Virtual Host

  1. Install QEMU guest agent: apt install qemu-guest-agent

Networking

Network Manager

Using ifupdown (alternative 1, default):

  1. For VLAN support, install vlan.
  2. For bonding/LACP support, install ifenslave.
  3. Configure /etc/network/interfaces.
  4. Run ifdown and ifup on all changed interfaces.

Using ifupdown2 (alternative 2):

  1. Install ifupdown2.
  2. Configure /etc/network/interfaces.
  3. Run ifdown and ifup on all changed interfaces.

Using systemd-networkd (alternative 3):

  1. Add a simple network config: Create /etc/systemd/network/lan.network based on main.network.
  2. Disable/remove the ifupdown config: mv /etc/network/interfaces /etc/network/interfaces.old
  3. Enable and (re)start systemd-networkd: systemctl enable systemd-networkd
  4. Purge ifupdown and ifupdown2.
  5. Check status: networkctl [status [-a]]
  6. Restart the system and check if still working. This will also kill any dhclient daemons which could trigger a DHCP renew at some point.

DNS

Manual (default, alternative 1):

  1. Manually configure /etc/resolv.conf.

Using systemd-resolved (alternative 2):

  1. Configure /etc/systemd/resolved.conf
    • DNS: A space-separated list of DNS servers.
    • Domains: A space-separated list of search domains.
  2. (Optional) If you're hosting a DNS server on this machine, set DNSStubListener=no to avoid binding to port 53.
  3. Enable and start systemd-resolved.service.
  4. Point /etc/resolv.conf to the one generated by systemd: ln -sf /run/systemd/resolve/stub-resolv.conf /etc/resolv.conf
  5. Check status: resolvectl

NTP

  1. Set the timezone: timedatectl set-timezone Europe/Oslo
  2. Enable network time: timedatectl set-ntp true
  3. Configure /etc/systemd/timesyncd.conf:
    • NTP (optional): A space-separated list of NTP servers. The defaults are fine.
  4. Restart systemd-timesyncd.
  5. Check status works: timedatectl and timedatectl timesync-status (check which servers are used)

Firewall

  1. Install apt install iptables iptables-persistent netfilter-persistent
    • Don't save the current rules when it asks.
  2. Make a simple iptables script or something.

Miscellanea

  1. Make sure IPv6 and NDP is configured securely:
    • If IPv6 and NDP is enabled and accepting RAs on insecure (i.e. public-facing) interfaces, the server may autoconfigure itself for those interfaces.
    • ifupdown with inet6 static does not use autoconfiguration.
    • By configuration: Disable "Accept-RA" on interfaces that should not autoconfigure themselves. It's typically enabled by default.
    • By firewalling (not recommended if avoidable): Block ICMPv6/NDP on untrusted interfaces so that the host can't autoconfigure itself. This prevents all IPv6 configuration for the interface, but may be required in some cases.
  2. Reboot and make sure everything still works.

Extra

Everything here is optional.

  • Setup Fail2Ban:
    • Recommended for public-facing servers.
    • Fix the firewall first so it configures itself correctly wrt. which firewall is used.
    • Install: apt install fail2ban
    • Check status: fail2ban-client status [sshd]
    • See Linux Server Applications: Fail2Ban for more info.
  • Set up a swap file:
    1. Note: You should have enough memory installed to never need swapping, but it's a nice backup to prevent the system from potentially crashing if anything bugs out and eats up too much memory.
    2. Show if swap is already enabled: swapon --show
    3. Allocate the swap file: fallocate -l <size> /swapfile
      • Alternatively, use dd.
    4. Fix the permissions: chmod 600 /swapfile
    5. Setup the swap file: mkswap /swapfile
    6. Activate the swap file: swapon /swapfile
      • Check: swapon --show
    7. Add it to fstab using this line: /swapfile swap swap defaults 0 0
      • Check: mount -a
  • Setup Postfix mail relay: See Linux Server Applications: Postfix.
  • Prevent root local login:
    • Alternatively, keep it enabled with a strong password as a local backdoor for recovery or similar.
    • Add a personal user first.
    • Check that the password field (the second field) for root in /etc/shadow is something invalid like "*" or "!", but not empty and not valid password hash. This prevents password login.
    • Clear /etc/securetty to prevent root local/console login.
  • Extra package security:
    • Install apt-listbugs and apt-listchanges and run them before upgrading a package.
    • Install needrestart and run it after upgrading.
    • Install debsums and run it after upgrading to check deb checksums.
    • Install debsecan to get automatically alerted when new vulnerabilities are discovered and security updates are available.
  • Google Authenticator 2FA:
    • Potentially useful for public-facing servers.
    • TODO
  • Install and run Lynis security auditor:
    • Install: apt install lynis
    • Run: lynis audit system
  • MOTD:
    • Clear /etc/motd and /etc/issue.
    • Download dmotd.sh to /etc/profile.d/.
    • Install the dependencies: neofetch lolcat
    • Add an ASCII art (or Unicode art) logo to /etc/logo, using e.g. TAAG.
    • (Optional) Add a MOTD to /etc/motd.
    • (Optional) Clear or change the pre-login message in /etc/issue.
    • Test it: su - <some-normal-user>
  • Monitor free disk space:
    • Download disk-space-checker.sh either to /cron/cron.daily/ or to /opt/bin and create a cron job for it.
    • Example cron job (15 minutes past every 4 hours): 15 */4 * * * root /opt/bin/disk-space-checker
    • Configure which disks/file systems it should exclude and how full they should be before it sends an email alert.

Troubleshooting

  • network-online.target is stalling during boot:
    • See all services it depends on: systemctl show -p WantedBy network-online.target
    • Disable the unused services which stall.
  • Firmware for the network card fails to load:
    • Causes a syslog record like "firmware: failed to load rtl_nic/rtl8168g-3.fw (-2)" when trying to up the interface.
    • Might happen after installation even if working initially (for some reason).
    • Realtek solution: Enable the "non-free" repo and install "firmware-realtek".
  • Perl complains about a locale error:
    • Test with perl -e exit. It will complain if there's an error.
    • Check the locale: locale
    • Comment AcceptEnv LANG LC_* in /etc/ssh/sshd_config to prevent clients bringing their own locale.

Miscellanea

Cron

  • Don't use periods (including file extensions) in the hourly/daily/weekly/monthly scripts.

{% include footer.md %}