Linux & Command Line
Working in the shell and running a Linux system: the commands you type every day, how to combine them, and how to manage users, software, services, storage and security from a terminal.
19 pages 108 glossary terms Linux+ Linux Essentials
How to use this topic
The first pages teach the shell itself — moving around, working with files and text, pipes and searching. The middle pages cover administration: users and permissions, processes, packages, services, logs, networking and remote work. The last pages add scripting, scheduling, archives, storage, security and troubleshooting. For what an operating system does under the hood, and for Windows and macOS, see Operating Systems. Writing robust scripts, in Bash and PowerShell side by side, has its own topic: Bash & PowerShell Scripting.
Shell examples marked Bash are complete and were
run exactly as shown: in an empty folder, as an ordinary user,
without network access. Commands that change the system — installing
packages, managing services or disks — are shown as terminal
sessions with illustrative output; try those on a test machine or
virtual machine, never first on a server others depend on. Examples
ran with LC_ALL=C.UTF-8. In English locales,
ls, glob sorting and sort ignore dots,
dashes and case at first, so your order may differ;
LC_ALL=C gives byte order.
Pages marked Linux+ cover material from the CompTIA Linux+ exam; pages also marked Linux Essentials cover the entry-level Linux Professional Institute (LPI) Linux Essentials exam.
Learning path
- 01The Shell and the TerminalWhat a shell is, how a command is built from a name, options and arguments, and the habits that make the command line fast: help pages, tab completion and history.
- 02Navigating the File SystemFinding your way around a Linux system from the command line: the directory tree, absolute and relative paths, and the commands pwd, cd and ls.
- 03Working with Files and DirectoriesCreating, copying, moving, renaming and deleting files and directories, wildcards, and hard and symbolic links.
- 04Viewing and Editing TextReading files with cat, less, head and tail, following a log live, and editing configuration files with nano and vim.
- 05Pipes, Redirection and FiltersConnecting small commands into powerful ones: standard input, output and error, redirection, pipes, and filters such as sort, uniq, cut and tr.
- 06Searching with grep, find and Regular ExpressionsFinding text inside files with grep, finding files with find, and describing patterns with regular expressions.
- 07Users, Groups and Permissions in PracticeManaging accounts and access on Linux: users and groups, ownership, permission bits, umask, special permissions and sudo.
- 08Processes and JobsSeeing and controlling what runs: ps, top and htop, signals and kill, and running commands in the background with jobs, bg, fg and nohup.
- 09Package ManagementInstalling, updating and removing software the Linux way: packages, repositories, apt and dnf, and universal formats such as Snap and Flatpak.
- 10Services and systemdManaging background services with systemd: units, systemctl, starting versus enabling, and reading service logs with journalctl.
- 11Logs and MonitoringFinding out what a system is doing: log files and the journal, disk and memory usage, load and uptime.
- 12Networking from the Command LineChecking and configuring the network on Linux: ip, ss, ping, dig and curl, NetworkManager, and host firewalls with ufw and firewalld.
- 13SSH and Remote WorkWorking on remote Linux machines: SSH keys and the client config file, copying files with scp and rsync, and keeping sessions alive with tmux.
- 14Shell Scripting BasicsWriting small bash scripts: the shebang, variables and quoting, conditions, loops, exit codes and functions.
- 15Scheduling TasksRunning commands automatically: cron and crontab syntax, systemd timers, and one-off jobs with at.
- 16Archives and CompressionBundling and compressing files with tar, gzip, xz and zip, and using them for simple backups.
- 17Storage in PracticeManaging disks on a Linux system: lsblk and blkid, mounting and /etc/fstab, LVM, and what to do when a disk fills up.
- 18Linux Security BasicsKeeping a Linux system safe: updates, least privilege and sudo, SSH hardening, host firewalls, SELinux and AppArmor, and watching the logs.
- 19Troubleshooting LinuxA practical approach to common Linux problems: a service that won't start, a full disk, permission denied, network trouble and a system that won't boot.
Linux & Command Line glossary
Short definitions of the terms used in this topic. The full glossary covers every topic.