Debian tutorials

Install Podman on Debian 12 Bookworm and Debian 13 Trixie with apt, compare 4.3.x and 5.4.x package branches, verify with podman info, test rootless mode, and run a hello container.

Read LeakSanitizer and Valgrind reports down to the line that owns the memory, use the flags that add detail, attribute growth with Massif, and query a running process with vgdb so you fix the cause instead of only …

Diagnose libc.so.6 errors by message type — GLIBC_2.xx not found, cannot open shared object file, wrong ELF class, or damaged system libc — then fix with the matching glibc package, multilib, rebuild, container, or …

Install Fail2ban, enable the sshd jail with sane bantime and ignoreip values, verify bans after failed SSH logins on RHEL and Debian, and unban trusted client addresses when needed.

Fix Vim E325 Found a swap file by the name by reading the .swp prompt, recovering after a crash, or removing a stale swap file once no editor owns it — not Linux swap memory from mkswap.

Diagnose SSH no route to host with TCP port tests, ip route get, remote firewalld and sshd checks, and learn when the message means a firewall REJECT instead of a missing route.

Set ClientAliveInterval and ClientAliveCountMax on sshd to drop unresponsive SSH clients, use ServerAliveInterval on the OpenSSH client to keep sessions alive through NAT, and understand how TCPKeepAlive differs.

Install rkhunter from EPEL or apt, update its signature database, baseline file properties with propupd, run a non-interactive check, and interpret warnings in rkhunter.log on RHEL and Debian-family hosts.

Create a custom systemd .service unit under /etc/systemd/system/, explain Unit Service and Install sections, start and enable it with systemctl, and verify with status and journalctl.

Take GNU tar listed-incremental backups with a snapshot file, create level 0 and level 1 archives, inspect Y and N file status, and restore by applying the full backup then each incremental in order.

Reuse one authenticated SSH connection for later ssh, scp, and sftp sessions with ControlMaster, ControlPath, and ControlPersist on the OpenSSH client.

Copy a directory and its contents between Linux hosts with scp -r and rsync -av over SSH, verify the remote layout, and avoid common path mistakes with trailing slashes.

Restrict SFTP users to a chroot directory with OpenSSH ChrootDirectory, ForceCommand internal-sftp, Match blocks in sshd_config, writable upload folders, and SSH public-key authentication.

Set SFTP upload permissions with OpenSSH internal-sftp -u in sshd_config, apply umask per user or group with Match blocks, and understand why umask removes bits but cannot add them.

Use pkill -P PARENT_PID . to send SIGTERM to every direct child of a parent process, list them with ps --ppid, and clean up script workers with pkill -P $$ . on EXIT.

Automate SFTP file transfers in Linux shell scripts using sftp batch mode with SSH keys, or password authentication with sshpass or expect when keys are not available.

Install ARPACK runtime and development packages on Ubuntu, Debian, and RHEL-family Linux from distribution repositories, verify libraries with dpkg or rpm and pkg-config, and link a sample Fortran program against …

Add a user to a supplementary group in Linux with usermod -aG, gpasswd -a, or adduser on Debian. Verify with id, apply changes with newgrp or re-login, and avoid the missing -a mistake.

Manage Linux users and groups with useradd, usermod, userdel, groupadd, primary and supplementary groups, account defaults, and ownership checks.

Configure Chrony NTP on Linux, verify time synchronization with chronyc, force clock correction, troubleshoot sync problems, and optionally serve LAN clients.

Learn the Linux boot process from UEFI or BIOS through GRUB, the kernel, initramfs, and systemd, with inspection commands and troubleshooting.

Use perf stat, perf record, and perf report on Linux to find CPU bottlenecks, collect call graphs, and resolve symbols with debuginfod on Rocky Linux, RHEL, Debian, Ubuntu, and other distributions.

Learn how to check ML-KEM support in TLS, create ML-DSA signatures, and verify post-quantum SSH key exchange on Linux, with tested Rocky Linux examples.

When a Linux VM shows the wrong time after every reboot, trace the clock from the virtual RTC through chrony, identify the selected NTP source, and fix stale RTC values, unsuitable chrony sources, or hypervisor time-sync …

Configure Apache HTTP Server to authenticate and authorize users with OpenLDAP using mod_authnz_ldap, group restrictions, TLS, and practical troubleshooting.

Fix missing Bash history commands in Linux, including commands lost across multiple terminals, delayed .bash_history writes, HISTCONTROL exclusions, and permission problems.

Create a Linux man page with a reusable groff template. Learn man sections, macros, local preview, system and user installation, mandb, whatis, and troubleshooting.

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.

Restart or reload cron in Linux with systemctl restart cron on Ubuntu and Debian or crond on RHEL and Rocky Linux, and when a reload is actually needed.

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.