Explanation¶

Explanation pages help you understand why things work the way they do: the design behind a subsystem, its history, the trade-offs between alternatives, and how the pieces fit together. They don't give step-by-step instructions.

Foundations¶

• Users, groups and permissions: How Linux identifies users and groups, how the kernel decides whether a process may access a file, why root is special, and where sudo and mandatory access control fit in.

Boot and init¶

• OpenRC and other init systems: What an init system does, how OpenRC approaches it, and how that compares with systemd, SysV init, runit, s6 and dinit.
• The Linux boot process: How a machine gets from power-on to a login prompt, what each stage hands to the next, and why knowing where a boot failed tells you where to fix it.

Software management¶

• Binary and source distributions: Why most distributions ship pre-built packages while Gentoo builds from source, what USE flags, profiles and binary package hosts change, and how rolling and point releases differ.
• How package management works: What a package is, how repositories, metadata and signatures establish trust, how dependencies are resolved and changes applied as transactions, and why apt, dnf, pacman and Portage differ.

Storage¶

• The Linux storage stack: How block devices, partitions, device-mapper, LVM, software RAID, encryption, filesystems and the VFS fit together, and what each layer gives and costs.

Processes and performance¶

• Control groups: What cgroups v2 are, how the hierarchy and controllers fit together, how systemd and OpenRC organise services with them, and how limits and accounting work.
• Load average and memory: What the Linux load average really counts, why it includes processes waiting for disks, and how to read memory figures such as free, available, page cache, swap and the OOM killer.
• Processes and signals: How Linux creates and tracks processes, what their states mean, how signals are delivered and handled, and how the shell's job control is built on them.

Networking fundamentals¶

• How Linux routes packets: How the kernel chooses where each IP packet goes, from routing tables and longest-prefix match to policy rules, neighbour discovery and the netfilter hooks around the routing decision.

Network services¶

• How SSH authentication works: How an SSH connection is secured, how the client and server prove who they are, what the agent does, and why keys are safer than passwords.

Network security¶

• Netfilter architecture: How netfilter hooks, connection tracking and nftables fit together, why nftables replaced iptables, and where firewalld and ufw sit on top.

Host security and hardening¶

• How PAM works: How Linux-PAM stacks modules into authentication, account, password and session checks, how control flags decide the outcome, and why a small mistake can lock everyone out.
• SELinux and AppArmor: What mandatory access control adds to ordinary Unix permissions, how SELinux labels and AppArmor path profiles differ, what their modes mean, and which distributions turn which one on.
• Patching strategy: Why security updates matter, how advisories reach you, when an update needs a restart or reboot to take effect, what live patching does, and how staging and rollback keep patching safe.

Logging, monitoring and observability¶

• Linux logging architecture: How log messages travel from the kernel and programs through journald and syslog daemons to memory, disk and other machines, and why each distribution family wires these parts together differently.

Troubleshooting¶

• A troubleshooting method: Why a disciplined, hypothesis-driven approach finds faults faster than guessing, and how to apply it layer by layer or along a request's path.

Automation and configuration management¶

• Idempotency and configuration management: Why describing the state a server should be in beats scripting the steps to get there, what idempotency and drift mean, how push and pull tools differ, and why configuration belongs in version control.
• cron and systemd timers: How cron and systemd timers decide when to run a job, how they differ in logging, dependencies, missed runs and randomised delays, and what schedules jobs on Gentoo with OpenRC.