Glossary

198 terms

# A B C D E F G H I J K L M N O P R S T U V W X Z

#

.gitignore — A file listing paths git should not track
.vimrc — Vim's configuration file, customising options, mappings, and plugins
/boot — The directory holding kernel images, initramfs, and bootloader files
/dev — The directory containing device nodes for hardware and virtual devices
/dev/null — A device that discards all data written to it and returns EOF on read
/dev/random — A device returning cryptographically strong random bytes from the kernel's entropy pool
/dev/zero — A device that returns an endless stream of null bytes when read
/etc — Host-specific configuration files for the system and its services
/etc/group — The file listing groups and their members
/etc/hosts — A static mapping from hostnames to IP addresses, predating DNS
/etc/passwd — The file listing user accounts and their basic attributes
/etc/resolv.conf — The DNS resolver configuration file
/etc/shadow — The file holding hashed passwords and account aging information
/home — The directory holding users' personal files and configuration
/opt — Directory for optional, third-party, self-contained software packages
/proc — A virtual filesystem exposing kernel and process information as files
/run — A tmpfs holding volatile runtime data produced by the system and services
/srv — Data served by the system to other machines, such as web or FTP content
/sys — A virtual filesystem exposing kernel devices and subsystems
/tmp — A world-writable directory for temporary files
/usr — Secondary hierarchy containing the bulk of user-installed system software
/var — Variable data: logs, spools, caches, and state written during normal operation

A

ACL — Access Control Lists, extending Unix permissions with per-user and per-group entries
Alias — A shell shortcut that expands to a longer command
Alpine Linux — A small, security-oriented distribution popular in containers
AppArmor — A Linux kernel security module providing path-based mandatory access control
AppImage — A self-contained, portable application file format
apt — The high-level package manager for Debian and Ubuntu
Arch Linux — A minimalist, rolling-release Linux distribution for experienced users
awk — A pattern-scanning and processing language for structured text

B

bash — The GNU Bourne Again Shell, the default shell of most Linux distributions
BIOS — The legacy firmware interface for PC-compatible hardware
BSD — The Berkeley Software Distribution, an influential family of Unix variants
btrfs — A copy-on-write filesystem with snapshots, checksums, and integrated volume management

C

Capabilities — Fine-grained subdivisions of root privilege that can be granted to processes
cat — Concatenate files to standard output
cgroup — Kernel feature for grouping processes and controlling their resource use
chmod — Change the permissions of files and directories
chown — Change the owner and group of a file or directory
Container — An isolated, packaged runtime environment sharing the host kernel
Container Image — A layered, read-only snapshot of a filesystem used to create containers
curl — A command-line tool for transferring data with URLs
cut — Extract sections (fields or characters) from each line of input

D

Daemon — A background process that runs without direct user interaction, typically providing a service
Debian — A long-standing community-driven Linux distribution known for stability and free software principles
Device File — A special file representing a hardware or virtual device to user space
Distribution — A complete Linux-based operating system combining kernel, userland, and package management
dmesg — Command and ring buffer holding kernel log messages
dnf — The modern high-level package manager for Fedora and RHEL
DNS — The Domain Name System, mapping names to IP addresses
Docker — The container platform that popularised the technology
Dockerfile — A script describing how to build a container image
Dotfile — A file whose name begins with a dot, hidden by default from ls
dpkg — The low-level Debian package manager

E

eBPF — A kernel technology for running sandboxed programs at safe attach points
Emacs — A highly extensible, self-documenting text editor
Environment Variable — A named value in a process's environment, inherited by child processes
exec — A family of system calls that replace the current process with a new program
Exit Code — A numeric status returned by a program when it terminates
ext4 — The default journalling filesystem for most Linux distributions

F

fail2ban — A service that watches log files and bans IPs exhibiting malicious behaviour
Fedora — A community-driven, leading-edge Linux distribution sponsored by Red Hat
File Descriptor — A non-negative integer identifying an open file within a process
Filesystem Hierarchy Standard — The convention defining the layout of directories on Unix-like systems
find — Search for files in a directory tree by name, type, size, time, or other criteria
fish — The friendly interactive shell, optimised for usability out of the box
Flatpak — A cross-distribution packaging format for Linux desktop applications
fork — A system call that creates a new process by duplicating the caller
Free Software — Software that respects users' freedoms to run, study, modify, and share it
fstab — /etc/fstab: the static filesystem table consulted at boot

G

Git — The distributed version control system that underlies most modern software development
Git Branch — A movable pointer to a commit, representing an independent line of development
Git Commit — A snapshot of the repository at a point in time, with a message
Git Merge — Combining the work of two branches into one
Git Rebase — Moving or modifying a series of commits onto a new base
Git Remote — A named reference to another git repository, usually hosted elsewhere
Git Repository — A directory tracked by git, containing files and their complete history
Glob — Shell-level wildcard pattern matching for filenames
GNOME — The GNU Network Object Model Environment, a major Linux desktop environment
GNU — A free software project and set of tools forming the userland of most Linux distributions
GPL — The GNU General Public License, a copyleft free-software licence
grep — A tool for searching text using patterns
GRUB — The GRand Unified Bootloader, the most common Linux bootloader

H

Hard Link — A directory entry that is a second name for an existing inode
head — Print the first N lines of input
Here Document — Shell syntax for embedding a multi-line string as input to a command
htop — An interactive process viewer, more user-friendly than top

I

init — The first user-space process started by the kernel, ancestor of all others
initramfs — The modern form of initial ramdisk: a cpio archive unpacked into a tmpfs at boot
initrd — An initial ramdisk loaded by the bootloader to help the kernel mount its root filesystem
Inode — A filesystem data structure storing metadata about a file
iostat — Report CPU and block device I/O statistics
IP Address — A numeric identifier assigned to a host on an IP network
ip command — The iproute2 command for network interface, address, and routing configuration
iptables — The classic Linux firewall command, configuring kernel packet filtering

J

Job Control — Shell feature for suspending, resuming, and backgrounding commands
journalctl — The command-line interface to systemd's binary journal logs
Journaling — A filesystem technique that logs pending changes to ensure crash consistency

K

KDE Plasma — A highly customisable desktop environment built on Qt
Kernel — The core of an operating system that manages hardware and provides services to user programs
Kernel Module — Code that can be loaded into and unloaded from the running kernel on demand
Kernel Space — The privileged memory and execution context of the operating system kernel
Kubernetes — An open-source container orchestration platform

L

less — An interactive pager for viewing text files one screen at a time
Linux — A free, open-source, Unix-like operating system kernel and the ecosystem built around it
Linux Namespace — A kernel feature isolating one or more global system resources for a set of processes
Load Average — A moving average of the number of processes competing for CPU or waiting on I/O
locate — Find files by name using a prebuilt database

M

Microkernel — A minimal kernel design where most OS services run as user-space processes
Monolithic Kernel — A kernel design in which all OS services run in a single privileged address space
mount — The operation (and command) that attaches a filesystem to a directory in the tree

N

nano — A friendly, modeless text editor for the terminal
nftables — The modern replacement for iptables, ip6tables, arptables, and ebtables
nice — A value that biases CPU scheduling priority of a process
NixOS — A Linux distribution built around the Nix package manager, with reproducible and declarative configuration

O

OOM Killer — The kernel mechanism that kills processes when memory is exhausted
Open Source — Software whose source code is available for inspection, modification, and redistribution
Orphan Process — A process whose parent has exited; adopted by init

P

Package Manager — Software that installs, upgrades, and removes packaged software on a system
pacman — The package manager of Arch Linux
PATH — An environment variable listing directories searched for executable commands
perf — Linux's kernel-integrated performance analysis tool
PID — Process identifier, a unique number identifying a running process
ping — Send ICMP echo requests to test network reachability
Pipe — A mechanism that connects the stdout of one process to the stdin of another
Podman — A daemonless, rootless container engine developed by Red Hat
Port — A 16-bit number identifying an endpoint on a host for TCP or UDP traffic
Positional Parameters — Script arguments accessed via $1, $2, and related shell variables
POSIX — A family of IEEE standards defining a portable operating system interface
Process — A running instance of a program, with its own memory and execution state
ps — Report a snapshot of current processes

R

Red Hat Enterprise Linux — A commercial enterprise-focused Linux distribution from Red Hat
Redirection — Shell syntax for connecting file descriptors to files or other descriptors
Regular Expression — A formal pattern language for matching text
Root — The superuser account with unrestricted privileges on a Linux system
rpm — The RPM Package Manager, used by Red Hat, Fedora, and SUSE
rsync — Fast, incremental file-transfer and synchronisation tool

S

sed — A stream editor for text transformation
SELinux — Security-Enhanced Linux, a mandatory access control system
set -e — Shell option that causes the script to exit immediately on any error
setgid — A permission bit affecting group ownership, with different meanings for files and directories
setuid — A permission bit causing a program to run with the privileges of its owner
Shebang — The #! line at the start of a script, telling the kernel which interpreter to use
Shell — A command-line interpreter that reads commands and dispatches them to the system
Shell Script — A text file containing shell commands, executed as a program
SIGHUP — The hangup signal, now widely used to request configuration reload
SIGKILL — The unblockable kill signal, forcibly terminating a process
Signal — An asynchronous notification sent to a process by the kernel or another process
SIGTERM — The standard termination signal, requesting a process to exit cleanly
Snap — A cross-distribution packaging format developed by Canonical
Socket — An endpoint for inter-process communication, locally or over a network
sort — Sort lines of text
ss — Socket statistics; a modern replacement for netstat
SSH — The Secure Shell protocol for authenticated, encrypted remote access
SSH Key — A public/private key pair used for SSH authentication
stderr — Standard error, file descriptor 2, the stream for diagnostic and error messages
stdin — Standard input, file descriptor 0, the default source of input for a program
stdout — Standard output, file descriptor 1, the default destination for a program's output
Sticky Bit — A permission bit on directories that restricts deletion to the file owner
strace — Trace the system calls a process makes
sudo — Run a command as another user, typically root, after authentication
Symbolic Link — A file that is a pointer to another file by name
System Call — A request from a user-space program for a service from the kernel
systemctl — The command-line client for controlling systemd
systemd — The init system and service manager used by most modern Linux distributions
systemd Target — A grouping of units that together represent a system state, similar to a runlevel
systemd Unit — A declarative description of something systemd manages
systemd-boot — A simple UEFI bootloader bundled with systemd

T

tail — Print the last N lines of input, optionally following a file as it grows
TCP/IP — The suite of protocols that underlies the Internet
tee — A command that reads stdin and writes it to both stdout and one or more files
Terminal — A text-based interface for interacting with the shell and other programs
tmpfs — A memory-backed filesystem whose contents vanish when unmounted or on reboot
top — Dynamic real-time view of running processes and system resource usage
traceroute — Display the route packets take to reach a host
tty — A terminal device, historically a teletypewriter; in Linux, a text console

U

Ubuntu — A user-friendly Debian-based distribution from Canonical
UEFI — The modern firmware interface for PCs and servers, replacement for legacy BIOS
ufw — Uncomplicated Firewall, a high-level front-end for iptables/nftables
umask — A bitmask that removes default permissions from newly created files
uniq — Filter out or count adjacent duplicate lines
Unix — A foundational multi-user operating system developed at Bell Labs from 1969 onwards
User Space — The region of memory and privilege level where ordinary programs run
useradd — Low-level command for creating user accounts

V

vi — The classic Unix visual editor, ancestor of Vim
Vim — Vi IMproved, the dominant terminal text editor on Linux
Virtual Machine — A software emulation of a complete computer, running its own kernel
vmstat — Report virtual memory, CPU, and I/O statistics at a chosen interval

W

Wayland — The modern display protocol replacing X11 on Linux
wc — Word, line, character, and byte counter
wget — A command-line tool for downloading files over HTTP, HTTPS, and FTP

X

X11 — The long-standing graphical display protocol for Unix-like systems
xargs — Build and execute command lines from stdin
XFCE — A lightweight GTK-based desktop environment
xfs — A high-performance journalling filesystem optimised for large files and parallelism

Z

ZFS — A sophisticated copy-on-write filesystem and volume manager originally from Sun
Zombie Process — A terminated process still occupying the process table until its parent reaps it
zsh — A powerful interactive shell with extensive customisation and plug-in ecosystem