Skip to content

Linux glossary

Curated terms for REBASH Linux Mastery. Keep entries short and practical.

  • ACL — Access Control List; extra file permissions beyond owner/group/other.
  • AppArmor — Linux Security Module that confines programmes with path-based profiles (common on Ubuntu).
  • apt — Debian/Ubuntu package manager front end (apt / apt-get).
  • BIOS — Basic Input/Output System; older firmware that starts the boot process.
  • bootloader — Software (often GRUB) that loads the kernel and initramfs.
  • cgroup — Control group; kernel feature that limits and accounts CPU, memory, and I/O for process groups.
  • CI/CD — Continuous Integration / Continuous Delivery (or Deployment).
  • cron — Time-based job scheduler for recurring commands.
  • DAC — Discretionary Access Control; classic Unix owner/group/other permissions.
  • df — Report free disk space on mounted filesystems (blocks and, with -i, inodes).
  • distribution (distro) — A complete Linux OS: kernel plus user space, package manager, and release policy.
  • DNS — Domain Name System; maps names to IP addresses.
  • dnf — Package manager used on many RHEL-family systems.
  • DR — Disaster Recovery; plan and practise to restore service after a major failure.
  • FHS — Filesystem Hierarchy Standard; conventional layout of /etc, /var, /usr, and related paths.
  • firewall — Host or network filter that allows or denies traffic (for example UFW or nftables).
  • GID — Group ID; numeric identity of a group.
  • GRUB — GRand Unified Bootloader; common bootloader on Ubuntu and many servers.
  • hard link — Another directory entry for the same inode on one filesystem.
  • HTTP / HTTPS — Hypertext Transfer Protocol (and its TLS-secured form) used by web services.
  • I/O — Input/Output; disk or network data movement.
  • IaC — Infrastructure as Code.
  • initramfs — Initial RAM filesystem loaded with the kernel for early boot drivers and root mount.
  • inode — Filesystem object that stores metadata and points to a file’s data blocks.
  • journald — systemd’s logging service; query with journalctl.
  • kernel — Core of Linux that manages CPU, memory, devices, and system calls.
  • LVM — Logical Volume Manager; flexible disk volumes above physical disks/partitions.
  • MAC — Mandatory Access Control (SELinux or AppArmor), enforced by policy beyond DAC.
  • mount point — Directory where a filesystem is attached into the tree.
  • namespace — Kernel isolation boundary (PID, mount, network, and others) used by containers.
  • OCI — Open Container Initiative; standard image and runtime formats.
  • PAM — Pluggable Authentication Modules; login and auth stack configuration.
  • PATH — Environment variable listing directories searched for executable commands.
  • PID — Process ID; number identifying a running process.
  • pipe — Connects stdout of one command to stdin of the next (|).
  • process — A running instance of a programme.
  • PTY / TTY — Pseudo-terminal / terminal device connecting a session to a shell.
  • RBAC — Role-Based Access Control.
  • RHEL — Red Hat Enterprise Linux and compatible distributions.
  • root — UID 0 superuser account, or the filesystem root /.
  • RPO — Recovery Point Objective; how much data loss (in time) is acceptable.
  • RTO — Recovery Time Objective; how quickly service must be restored.
  • SELinux — Security-Enhanced Linux; label-based MAC common on RHEL-family systems.
  • shell — Programme that reads and runs commands (for example bash).
  • SSH — Secure Shell; encrypted remote login and file transfer.
  • SRE — Site Reliability Engineering.
  • sticky bit — Directory mode bit so users can delete only their own files (typical on /tmp).
  • sudo — Run a command as another user (usually root) under policy.
  • symlink — Symbolic link; a path that points to another path (may cross filesystems).
  • systemd — Common init system and service manager (PID 1 on most modern servers).
  • target — systemd unit that groups other units into a desired system state (replaces old runlevels).
  • TCP — Transmission Control Protocol; reliable stream transport used by SSH and HTTP.
  • timer — systemd unit that activates another unit on a schedule.
  • UEFI — Unified Extensible Firmware Interface; modern firmware replacing classic BIOS.
  • UFW — Uncomplicated Firewall; simple front end to nftables/iptables on Ubuntu.
  • UID — User ID; numeric identity of a user account.
  • umask — Mask that controls default permissions for newly created files.
  • unit — systemd configuration object (service, timer, mount, target, and so on).
  • UUID — Universally Unique Identifier; stable disk/filesystem id for /etc/fstab.
  • VM — Virtual machine.
  • zombie process — Process that has exited but still has an entry until its parent reaps it.