VOCABULARY

Linux SysAdmin Vocabulary & Glossary

Comprehensive Glossary of Linux Terms, Commands, and Concepts

A

ACL (Access Control List): Extended file permissions beyond standard owner/group/other
AES (Advanced Encryption Standard): Symmetric encryption algorithm
AGP (Accelerated Graphics Port): Graphics card interface
ALSA (Advanced Linux Sound Architecture): Linux audio driver
API (Application Programming Interface): Interface for software communication
APM (Advanced Power Management): Power management standard
AppArmor: Linux security module for mandatory access control
apt (Advanced Package Tool): Debian/Ubuntu package manager
ARM (Advanced RISC Machines): CPU architecture
ATAPI (AT Attachment Packet Interface): Disk interface standard
ATA (AT Attachment): Disk interface standard
auditd: Linux audit daemon for security monitoring
awk: Pattern scanning and text processing language

B

Bash (Bourne Again Shell): Default Linux shell
BIND (Berkeley Internet Name Domain): DNS server software
BIOS (Basic Input/Output System): Firmware interface
booting: Process of starting the computer
bridge: Network device that connects two network segments
Btrfs: Copy-on-write filesystem for Linux
Burst RAM: Extra RAM that can be used temporarily

C

cache: Temporary storage for faster data access
CentOS: Community Enterprise Operating System (RHEL-based)
cgroups: Control groups for resource isolation
chroot: Change root directory
CLI (Command Line Interface): Text-based interface
cloud computing: On-demand computing resources
container: Lightweight virtualization technology
cron: Time-based job scheduler
CSR (Certificate Signing Request): Certificate request
curl: Command-line HTTP client
systemd: Modern system and service manager

D

daemon: Background process
DAS (Direct Attached Storage): Storage directly attached
dd: Data definition utility for disk operations
Debian: Linux distribution
DHCP (Dynamic Host Configuration Protocol): IP address assignment
DNS (Domain Name System): Domain name resolution
Docker: Container platform
Dovecot: IMAP/POP3 mail server
Dpkg: Debian package manager
DRAC (Dell Remote Access Controller): Remote management

E

EC2 (Elastic Compute Cloud): AWS compute service
EFI (Extensible Firmware Interface): Modern firmware interface
Encryption: Data protection mechanism
EOF (End of File): File ending marker
EPEL (Extra Packages for Enterprise Linux): Extra packages for RHEL
EPG (Electronic Program Guide): TV guide
ESXi: VMware hypervisor
ethtool: Network interface configuration tool
ext4: Fourth extended filesystem

F

FHS (Filesystem Hierarchy Standard): Linux directory structure
Firewall: Network security system
FQDN (Fully Qualified Domain Name): Complete domain name
fsck (File System Check): Filesystem repair utility
FTP (File Transfer Protocol): File transfer protocol

G

gateway: Network entry/exit point
GCC (GNU Compiler Collection): Compiler suite
GID (Group ID): Group identifier
GNOME: Desktop environment
GNU (GNU’s Not Unix): Free software project
GPL (General Public License): Open source license
GPT (GUID Partition Table): Modern partition scheme
GRUB (GRand Unified Bootloader): Bootloader
gpg: GNU Privacy Guard for encryption

H

HAL (Hardware Abstraction Layer): Hardware interface
HDMI (High-Definition Multimedia Interface): Audio/video interface
hostname: Computer network name
HP (Hewlett-Packard): Company
HTTP (Hypertext Transfer Protocol): Web protocol
htop: Interactive process viewer
Huge Pages: Large memory pages for performance

I

I/O (Input/Output): Data transfer
IDE (Integrated Development Environment): Development environment
init: First process in Linux (traditional)
inode: Filesystem metadata structure
IP (Internet Protocol): Network protocol
iptables: Linux firewall (legacy)
IPv4/IPv6: Internet Protocol versions
ISC (Internet Systems Consortium): Organization
ISO: Disk image format

J

Java: Programming language and platform
journalctl: Systemd journal viewer
jq: JSON processor

K

KDE: Desktop environment
kernel: Operating system core
Kubernetes: Container orchestration platform
KVM (Kernel-based Virtual Machine): Linux virtualization

L

LAMP: Linux, Apache, MySQL, PHP stack
LDAP (Lightweight Directory Access Protocol): Directory protocol
LFS (Linux From Scratch): Building Linux from source
LVM (Logical Volume Manager): Storage management
LZMA: Compression algorithm

M

MBR (Master Boot Record): Legacy boot sector
mdadm: Linux RAID management tool
MIME (Multipurpose Internet Mail Extensions): File type encoding
MTA (Mail Transfer Agent): Email transfer software
MTU (Maximum Transmission Unit): Network packet size
MySQL/MariaDB: Database systems

N

Nagios: Monitoring system
NAT (Network Address Translation): IP address translation
nftables: Modern Linux firewall (replacement for iptables)
NFS (Network File System): Network filesystem
NIC (Network Interface Card): Network hardware
nmap: Network scanner
ntpd: Network Time Protocol daemon
nginx: High-performance web server

O

OOM Killer: Out-of-Memory killer
OpenSSH: SSH implementation
OpenSSL: SSL/TLS toolkit
OSI Model: Network layer model

P

PAC (Proxy Auto-Config): Automatic proxy configuration
Package: Software distribution format
PAM (Pluggable Authentication Modules): Authentication framework
Partition: Disk division
PCI (Peripheral Component Interconnect): Computer bus
PID (Process ID): Process identifier
PNG (Portable Network Graphics): Image format
Postfix: Mail server
PostgreSQL: Database system
PowerShell: Microsoft shell
PXE (Preboot Execution Environment): Network boot

Q

qemu: Emulator and virtualizer
Quota: Disk usage limits

R

RAID (Redundant Array of Independent Disks): Storage redundancy
RAM (Random Access Memory): Memory
RDP (Remote Desktop Protocol): Remote access protocol
RHEL (Red Hat Enterprise Linux): Enterprise Linux
RPM (RPM Package Manager): Package format
rsync: File synchronization tool

S

S3: AWS storage service
samba: Windows file sharing
SASL (Simple Authentication and Security Layer): Authentication
SCA (Source Code Analysis): Code analysis
screen: Terminal multiplexer
SCSI (Small Computer System Interface): Interface standard
SELinux: Security-Enhanced Linux
SFTP: Secure FTP
SGID: Set Group ID
SHA (Secure Hash Algorithm): Hash function
SMB (Server Message Block): File sharing protocol
SMTP (Simple Mail Transfer Protocol): Email protocol
SNMP (Simple Network Management Protocol): Network management
socket: Network endpoint
SQL (Structured Query Language): Database language
SSH (Secure Shell): Secure remote access
SSL/TLS: Encryption protocols
SUID: Set User ID
swap: Virtual memory
syslog: System logging

T

tar: Tape archive utility
TCP (Transmission Control Protocol): Transport protocol
TFTP (Trivial FTP): Simple FTP
tmpfs: Temporary filesystem
Tomcat: Java application server
Torrent: Peer-to-peer protocol
TTL (Time To Live): Time limit

U

Ubuntu: Linux distribution
UDP (User Datagram Protocol): Transport protocol
UEFI: Unified Extensible Firmware Interface
UID (User ID): User identifier
UMask: Default permission mask
UPS (Uninterruptible Power Supply): Power backup
USB (Universal Serial Bus): Interface standard

V

Vagrant: Development environment tool
VFS (Virtual File System): Filesystem abstraction
Vim: Text editor
VM (Virtual Machine): Virtual computer
VPN (Virtual Private Network): Secure network tunnel
VRRP (Virtual Router Redundancy Protocol): Router redundancy

W

WebDAV: Web-based Distributed Authoring
WEP (Wired Equivalent Privacy): Wireless encryption
WPA (Wi-Fi Protected Access): Wireless security

X

X11: Window system
XFS: High-performance filesystem
XML (Extensible Markup Language): Markup language

Y

YAML (YAML Ain’t Markup Language): Data serialization
yum: Yellowdog Updater Modified (RHEL/CentOS)

Z

Zabbix: Monitoring solution
ZFS: Advanced filesystem
ZIP: Compression format
Zsh: Z shell

Common Commands Quick Reference

File Operations

Command	Description
`ls`	List directory contents
`ls -la`	List with hidden files and details
`cd`	Change directory
`pwd`	Print working directory
`cp`	Copy files
`cp -r`	Copy directories recursively
`mv`	Move/rename files
`rm`	Remove files
`rm -rf`	Force remove directories
`mkdir`	Create directory
`rmdir`	Remove empty directory
`touch`	Create empty file
`cat`	Display file contents
`less`	View file page by page
`head`	View first lines
`tail`	View last lines
`tail -f`	Follow file in real-time
`grep`	Search in files
`find`	Find files
`locate`	Find files using database
`chmod`	Change permissions
`chown`	Change ownership
`ln`	Create links
`tar`	Archive files
`gzip`	Compress files
`zip`	Create zip archives

System Information

Command	Description
`uname -a`	System information
`hostname`	Show/set hostname
`whoami`	Current user
`id`	User ID and groups
`uptime`	System uptime
`date`	Current date/time
`cal`	Calendar
`df`	Filesystem usage
`df -h`	Human-readable sizes
`du`	Directory space usage
`free -h`	Memory usage
`cat /proc/meminfo`	Detailed memory
`cat /proc/cpuinfo`	CPU info
`lscpu`	CPU details
`lsblk`	Block devices
`fdisk -l`	Partition table

Process Management

Command	Description
`ps`	List processes
`ps aux`	All processes detailed
`top`	Process monitor
`htop`	Interactive process viewer
`pkill`	Kill by name
`kill`	Send signal to process
`kill -9`	Force kill
`pstree`	Process tree
`nice`	Run with priority
`renice`	Change priority
`jobs`	Background jobs
`bg`	Resume in background
`fg`	Bring to foreground

Network

Command	Description
`ip addr`	Show IP addresses
`ip link`	Show interfaces
`ip route`	Show routing table
`ifconfig`	Configure network (legacy)
`ping`	Test connectivity
`traceroute`	Trace route
`mtr`	Combined ping/traceroute
`nslookup`	DNS lookup
`dig`	DNS lookup (detailed)
`host`	DNS lookup
`ss`	Socket statistics
`netstat`	Network statistics
`curl`	HTTP client
`wget`	Download files
`ssh`	Secure shell
`scp`	Secure copy
`rsync`	Remote sync

Package Management (Debian/Ubuntu)

Command	Description
`apt update`	Update package lists
`apt upgrade`	Upgrade packages
`apt install`	Install package
`apt remove`	Remove package
`apt search`	Search packages
`apt show`	Show package info
`dpkg -l`	List installed packages
`dpkg -i`	Install .deb file

Package Management (RHEL/CentOS)

Command	Description
`yum update`	Update packages
`yum install`	Install package
`yum remove`	Remove package
`yum search`	Search packages
`yum info`	Package information
`rpm -qa`	List installed packages
`rpm -i`	Install .rpm file

User Management

Command	Description
`useradd`	Create user
`usermod`	Modify user
`userdel`	Delete user
`passwd`	Change password
`groupadd`	Create group
`groupdel`	Delete group
`su`	Switch user
`sudo`	Execute as root
`who`	Show logged in users
`last`	Last logins

Permissions (Numeric)

Value	Permission
0	---
1	—x
2	-w-
3	-wx
4	r—
5	r-x
6	rw-
7	rwx

Systemctl Commands

Command	Description
`systemctl start`	Start service
`systemctl stop`	Stop service
`systemctl restart`	Restart service
`systemctl status`	Service status
`systemctl enable`	Enable at boot
`systemctl disable`	Disable at boot
`systemctl list-units`	List services
`systemctl daemon-reload`	Reload config

Logs

Command	Description
`journalctl`	View systemd journal
`journalctl -u`	Filter by unit
`journalctl -f`	Follow logs
`journalctl --since`	Filter by time
`tail -f`	Follow file
`less +F`	Follow with less
`dmesg`	Kernel messages

Disk Management

Command	Description
`fdisk -l`	List partitions
`fdisk`	Partition editor
`parted`	Partition manager
`mkfs`	Create filesystem
`fsck`	Filesystem check
`mount`	Mount filesystem
`umount`	Unmount filesystem
`df -h`	Show disk usage

LVM Commands

Command	Description
`pvcreate`	Create physical volume
`vgcreate`	Create volume group
`lvcreate`	Create logical volume
`lvextend`	Extend LV
`lvreduce`	Reduce LV
`pvs`	Show PVs
`vgs`	Show VGs
`lvs`	Show LVs

Firewall (iptables)

Command	Description
`iptables -L`	List rules
`iptables -A`	Append rule
`iptables -D`	Delete rule
`iptables -F`	Flush rules
`iptables -P`	Set policy
`iptables-save`	Save rules
`iptables-restore`	Restore rules

Firewall (firewalld)

Command	Description
`firewall-cmd --list-all`	List rules
`firewall-cmd --add-service`	Add service
`firewall-cmd --remove-service`	Remove service
`firewall-cmd --add-port`	Add port
`firewall-cmd --reload`	Reload config

Compression

Command	Description
`tar -cvf`	Create archive
`tar -xvf`	Extract archive
`tar -czvf`	Create gz archive
`tar -xzvf`	Extract gz archive
`gzip`	Compress file
`gunzip`	Decompress file
`zip`	Create zip
`unzip`	Extract zip

Text Processing

Command	Description
`awk`	Pattern scanning
`sed`	Stream editor
`sort`	Sort lines
`uniq`	Remove duplicates
`wc`	Word count
`cut`	Cut columns
`tr`	Translate characters
`head`	First lines
`tail`	Last lines

SSH Commands

Command	Description
`ssh user@host`	Connect to host
`ssh -p port`	Connect on port
`ssh-keygen`	Generate keys
`ssh-copy-id`	Copy public key
`scp file user@host:/path`	Copy to remote
`scp user@host:/file .`	Copy from remote

Important Paths

Path	Description
`/etc`	System configuration
`/var/log`	Log files
`/home`	User home directories
`/root`	Root user home
`/tmp`	Temporary files
`/opt`	Optional software
`/usr`	User programs
`/bin`	Essential commands
`/sbin`	System commands
`/proc`	Process information
`/sys`	System information
`/dev`	Device files

Common Ports

Port	Service
20/21	FTP
22	SSH
23	Telnet
25	SMTP
53	DNS
80	HTTP
110	POP3
143	IMAP
443	HTTPS
3306	MySQL/MariaDB
5432	PostgreSQL
6379	Redis
8080	HTTP Alternate
8443	HTTPS Alternate

Summary

This glossary covers essential Linux terminology and commands for system administration, organized alphabetically with quick reference tables for common operations.

Last Updated: February 2026