A glossary for the terms that appear in documentation and support tickets.
ROOT
The administrative account with unrestricted access. Powerful and dangerous in equal measure.
SSH
Secure Shell, the encrypted protocol used to access the command line remotely.
SUDO
Running a command with elevated privileges without logging in as root directly.
DAEMON or SERVICE
A program running in the background: your web server, database and mail server are all services.
PACKAGE MANAGER
The tool that installs and updates software. Usually apt on Debian and Ubuntu, dnf or yum on Rocky, AlmaLinux and CentOS.
FIREWALL
Software controlling which network connections are permitted. Commonly firewalld, ufw or CSF.
REVERSE PROXY
A server sitting in front of another, forwarding requests. Nginx is frequently used this way.
SWAP
Disk space used as overflow when memory is exhausted. Slow, but better than processes being killed.
CRON
The scheduler that runs commands at set times.
UPTIME and LOAD AVERAGE
How long since the last reboot, and how busy the system is.
