Key Linux terms and definitions.
| Term | Definition |
|---|---|
| ACL | Access Control List โ fine-grained permissions beyond rwx |
| AppArmor | MAC security module that uses path-based profiles (Ubuntu/SUSE) |
| APT | Advanced Package Tool โ Debian/Ubuntu package manager |
| Term | Definition |
|---|---|
| Bash | Bourne Again Shell โ the default shell on most Linux distros |
| Block device | Storage device that reads/writes data in fixed-size blocks (e.g., HDD, SSD) |
| Boot loader | Program that loads the kernel at startup (e.g., GRUB) |
| Btrfs | B-tree filesystem with snapshots, compression, and built-in RAID |
| Term | Definition |
|---|---|
| cgroups | Control groups โ limit and isolate resource usage per process group |
| Chroot | Change root โ run a process with a different root directory |
| CLI | Command Line Interface โ text-based terminal |
| Container | Lightweight isolation using namespaces and cgroups (e.g., Docker) |
| Cron | Time-based job scheduler daemon |
| Term | Definition |
|---|---|
| Daemon | Background service process (usually ends with d, e.g., sshd) |
| Device file | Special file in /dev/ representing hardware or virtual devices |
| Distro | Linux distribution โ complete OS built around the Linux kernel |
| DKMS | Dynamic Kernel Module Support โ auto-rebuilds modules on kernel upgrades |
| DNS | Domain Name System โ translates hostnames to IP addresses |
| Term | Definition |
|---|---|
| eBPF | Extended Berkeley Packet Filter โ run sandboxed programs in kernel space |
| Environment variable | Named value available to processes (e.g., $PATH, $HOME) |
| ext4 | Fourth extended filesystem โ standard Linux filesystem |
| Term | Definition |
|---|---|
| FHS | Filesystem Hierarchy Standard โ defines directory structure (/bin, /etc, etc.) |
| FOSS | Free and Open Source Software |
| fstab | /etc/fstab โ defines filesystems to mount at boot |
| Term | Definition |
|---|---|
| GNU | GNU's Not Unix โ the userspace tools that complement the Linux kernel |
| GRUB | GRand Unified Bootloader โ the standard Linux bootloader |
| GUI | Graphical User Interface โ desktop environment |
| Term | Definition |
|---|---|
| Hugepages | Large memory pages (2MB/1GB) for performance-sensitive apps |
| inode | Data structure storing file metadata (permissions, size, block locations) |
| initramfs | Initial RAM filesystem โ temporary root loaded during boot |
| iptables | Classic Linux firewall framework (being replaced by nftables) |
| Term | Definition |
|---|---|
| journalctl | Tool to query systemd's journal (logs) |
| Kernel | Core of the OS โ manages hardware, memory, processes |
| KVM | Kernel-based Virtual Machine โ Type 1 hypervisor built into Linux |
| Term | Definition |
|---|---|
| LFS | Linux From Scratch โ build a complete Linux system from source |
| LVM | Logical Volume Manager โ flexible disk management abstraction |
| Term | Definition |
|---|---|
| MAC | Mandatory Access Control โ system-enforced security (SELinux/AppArmor) |
| Module | Loadable kernel code (drivers, filesystems) โ load with modprobe |
| Mount | Attach a filesystem to a directory in the file tree |
| Term | Definition |
|---|---|
| Namespace | Kernel feature that isolates resources (PID, network, mount, etc.) |
| NFS | Network File System โ share directories over the network |
| nftables | Modern replacement for iptables |
| Term | Definition |
|---|---|
| OOM Killer | Out-of-Memory Killer โ terminates processes when RAM is exhausted |
| Package | Software bundle with binaries, configs, and dependency info |
| PID | Process ID โ unique number identifying a running process |
| Pipe | ` |
| Process | Running instance of a program |
| Term | Definition |
|---|---|
| RAID | Redundant Array of Independent Disks โ combine disks for performance/redundancy |
| Root | The superuser (UID 0) or the top-level directory (/) |
| rsync | Smart file synchronization tool โ only transfers changes |
| Term | Definition |
|---|---|
| SELinux | Security-Enhanced Linux โ MAC using security contexts (RHEL/Fedora) |
| Shell | Command interpreter โ accepts and executes commands (bash, zsh, fish) |
| Signal | Software interrupt sent to a process (e.g., SIGTERM, SIGKILL) |
| SSH | Secure Shell โ encrypted remote access protocol |
| Swap | Disk space used as overflow for RAM |
| Symlink | Symbolic link โ pointer to another file or directory |
| Systemd | The init system (PID 1) on most modern distros |
| sysctl | Modify kernel parameters at runtime |
| Term | Definition |
|---|---|
| TTY | TeleTYpewriter โ terminal device or virtual console |
| UEFI | Unified Extensible Firmware Interface โ modern BIOS replacement |
| UID | User ID โ numeric identifier for users |
| Term | Definition |
|---|---|
| VFS | Virtual File System โ kernel abstraction layer over all filesystems |
| WireGuard | Modern, fast VPN protocol built into the Linux kernel |
| Term | Definition |
|---|---|
| X11/Xorg | Legacy display server (being replaced by Wayland) |
| Wayland | Modern display server protocol |
| ZFS | Advanced filesystem with built-in RAID, snapshots, and checksums |
| Zombie | Terminated process whose exit status hasn't been collected by its parent |