Debian family tutorials

Create a system-level systemd service that starts at boot and runs as a dedicated non-root user and group on Ubuntu, Debian, Fedora, RHEL, Rocky Linux, AlmaLinux, CentOS Stream and Oracle Linux.

Learn how to restart the cron or crond service on Ubuntu, Debian, RHEL, Rocky Linux, AlmaLinux and CentOS, when a restart is required, and why crontab changes normally reload automatically.

Compare the RHEL and Debian Linux families, including RPM vs DEB, DNF vs APT, repositories, release models, lifecycle, security, support, configuration, cloud images and server use cases.

Learn how Unix, Linux, GNU/Linux and Linux distributions relate, why Ubuntu, Debian, Fedora, RHEL, Rocky Linux and Arch differ beyond desktop themes, and how to identify your distro from the shell.

Fix curl error 60 and similar HTTPS failures on Linux when corporate SSL inspection replaces public certificates with a private root CA trusted on Windows but missing from the Linux trust store.

Migrate an already-installed Ubuntu LVM root volume group onto a new LUKS2 physical volume with pvmove, then configure crypttab with initramfs, regenerate the initramfs, and update GRUB for boot-time unlock.

Use systemd-cryptenroll on LUKS2 volumes to add TPM2, FIDO2, PKCS#11, and recovery-key unlock methods, store token metadata in the LUKS2 JSON area, and wire boot unlock through crypttab.

Extend or shrink a LUKS2 ext4 volume on Linux: grow the partition first, run cryptsetup resize on the mapper, then resize2fs; for shrink, reverse the order with offline resize2fs and --size in 512-byte sectors.

Unlock and mount a LUKS USB or moved disk on another Linux host: cryptsetup open by device, UUID=, or /dev/disk/by-uuid, ext4 or LVM inside LUKS, read-only rescue mount, and close the mapper.

Configure crypttab and fstab to unlock and mount a secondary LUKS data partition at boot on Ubuntu or Debian.

Back up and restore a LUKS2 header with cryptsetup luksHeaderBackup and luksHeaderRestore, use a detached header file, and understand when a header copy cannot recover a forgotten passphrase.

Rotate LUKS passphrases and key slots, change cipher or volume key with cryptsetup reencrypt on LUKS2, and back up the header before destructive operations.

Encrypt a new Linux disk partition with LUKS2 using cryptsetup: partition the disk, run luksFormat, open the mapper, create ext4 on /dev/mapper, and mount the volume.

List users in Linux with getent, /etc/passwd, who, and id. Filter normal and system accounts, see logged-in sessions, and check whether a user exists on Ubuntu and RHEL.

Configure OpenSSH authentication in sshd_config: password, public key, keyboard-interactive, host-based, GSSAPI, AuthenticationMethods, and Match blocks on Linux.

List groups in Linux with getent, groups, id, and /etc/group. Check user group membership, list group members, and compare primary vs supplementary groups.

Install Node.js on Ubuntu with apt nodejs, NodeSource setup scripts, NVM for multiple versions, or the official nodejs.org linux-x64 tar.xz under /opt, verify with node --version and npm --version, and uninstall per …

Import a CA or TLS certificate into Java cacerts on Ubuntu, Debian, RHEL, and Rocky Linux with keytool -importcert: locate cacerts, use a copy for safe testing, default password changeit, and distro-specific system trust …

Fix keytool command not found on Ubuntu by installing OpenJDK (default-jdk or openjdk-21-jdk), set JAVA_HOME and PATH, verify with keytool -help, run a PKCS12 smoke test, update through apt, and uninstall cleanly.

Install OpenSSL on Ubuntu with apt (openssl and libssl-dev), verify with openssl version, understand when the distro package is enough versus building from source, and generate a test TLS key and certificate.

Compare Ubuntu 26.04 LTS and Linux Mint 22.3 in 2026: downstream Mint on Noble vs Canonical Ubuntu, GNOME vs Cinnamon, snap vs Flatpak policy, Mint tools, support timelines, hardware, developers, and which to install.

Compare Ubuntu 26.04 LTS and Fedora Linux 44 in 2026: Debian-derived APT vs RHEL-upstream DNF, five-year LTS vs 13-month releases, snap vs Flatpak, AppArmor vs SELinux, cloud and enterprise fit, and practical desktop …

Compare Ubuntu 26.04 LTS Server and Desktop in 2026: same archive and kernel, different metapackages, RAM and disk requirements, installers, headless vs GNOME, cloud images, adding a GUI, and when to pick each edition.

Unsupported two-hop downgrade Ubuntu 26.04 LTS to 25.04 via 25.10 using apt pinning and aptitude—no data loss under /home on our VirtualBox VM—reboot between hops, Python and GRUB failures, libc6 hybrid state, and when …

Upgrade Ubuntu 25.04 to 26.04 LTS with do-release-upgrade via the required 25.10 hop—no data loss on /home in our VirtualBox test—apt full-upgrade and reboot checks, and fixes when the upgrader blocks on a pending reboot …

List obsolete packages on Ubuntu with apt list ?obsolete, preview removal with apt-get -s, purge safely after do-release-upgrade, and distinguish obsolete packages from autoremove and rc config cleanup.

Downgrade Ubuntu 21.04 (Hirsute Hippo) to 20.04 LTS (Focal Fossa) with apt pinning, sources.list retargeting, and aptitude dist-upgrade—no data loss under /home when the run completes, plus dpkg recovery, reboot checks, …

Learn how to check Ubuntu version from the command line or GUI. Use lsb_release, /etc/os-release, hostnamectl, /etc/issue, or Settings to find your Ubuntu release, version number, codename, and kernel.

Compare Kubuntu 26.04 LTS and Ubuntu MATE 24.04/25.10 in 2026: KDE Plasma vs MATE desktop, support timelines, hardware fit, customization, Wayland, applications, and which official Ubuntu flavor to pick for your PC.

Compare Debian 12 Bookworm and Ubuntu 24.04 LTS Noble for servers: release cycles, security support, package freshness, Snap vs pure APT, cloud images, resource use, and when to pick each distro for production workloads.