.. include:: /global.rst .. _Glossary: *************************** OS Glossary *************************** Operating Systems terminology, ordered alphabetically. Each term lists the general branch of operating systems it falls under and a brief explanation. Search by Letter ================================= :ref:`0-9 ` | :ref:`A ` | :ref:`B ` | :ref:`C ` | :ref:`D ` | :ref:`E ` | :ref:`F ` | :ref:`G ` | :ref:`H ` | :ref:`I ` | :ref:`J ` | :ref:`K ` | :ref:`L ` | :ref:`M ` | :ref:`N ` | :ref:`O ` | :ref:`P ` | :ref:`Q ` | :ref:`R ` | :ref:`S ` | :ref:`T ` | :ref:`U ` | :ref:`V ` | :ref:`W ` | X | Y | Z .. _glossary-num: 0-9 ================================= 3-2-1 Backup Rule --------------------------------- **Branch:** Backup & Recovery Keep 3 copies of data on 2 kinds of media with 1 copy offsite :ref:`Back to top ` .. _glossary-a: A ================================= AAAA Record --------------------------------- **Branch:** Domain Management & Encryption A DNS record that maps a name to an IPv6 address, like an A Record does for IPv4 Access Control List (ACL) --------------------------------- **Branch:** Permissions A detailed list of which users or groups can access a resource and how ACID --------------------------------- **Branch:** Databases Atomicity, Consistency, Isolation and Durability: the four promises a reliable database transaction makes adduser / usermod -aG --------------------------------- **Branch:** User Management Creates a new user account / adds the user to a group Ansible --------------------------------- **Branch:** Server Configuration Management An automation tool that configures servers from written playbooks Apex Domain (@) --------------------------------- **Branch:** Domain Management & Encryption The bare domain with nothing in front, such as supersims21.org; written as @ in the Host column of DNS settings Application Server --------------------------------- **Branch:** Servers & Services Server that runs application code such as Java web apps, for example Tomcat apt update vs upgrade vs full-upgrade ------------------------------------- **Branch:** Security Refreshes the list of available packages / installs new versions of current packages / same but adds or removes packages when needed Attack Surface --------------------------------- **Branch:** Security All the points where an attacker could try to get into a system Authentication vs Authorization --------------------------------- **Branch:** Security Verifying who a user is versus deciding what they are allowed to do Autocommit --------------------------------- **Branch:** Databases A mode where each SQL statement is saved immediately as its own transaction AUTOINCREMENT / sqlite_sequence --------------------------------- **Branch:** SQLite Internals Keyword that stops SQLite from reusing ids / the internal table that remembers the highest id used :ref:`Back to top ` .. _glossary-b: B ================================= B-tree --------------------------------- **Branch:** SQLite Internals A balanced tree of pages that SQLite uses to store every table and index in sorted order Backup --------------------------------- **Branch:** Backup & Recovery A copy of data kept so it can be restored after loss or damage Bash Script --------------------------------- **Branch:** Command Line & Shell A text file of shell commands run together to automate tasks Bootloader --------------------------------- **Branch:** OS Overview & Components Program that loads the kernel into memory when the computer starts, such as GRUB Brute Force Attack --------------------------------- **Branch:** Security Repeatedly guessing passwords until one works :ref:`Back to top ` .. _glossary-c: C ================================= Certificate Authority (CA) --------------------------------- **Branch:** Domain Management & Encryption A trusted organization that issues digital certificates, such as Let's Encrypt CHECK Constraint --------------------------------- **Branch:** Databases A rule in a table definition that every row must pass, such as player_count >= 0 chmod / chown --------------------------------- **Branch:** Permissions Commands to change a file's permissions and to change its owner or group Client-Server Model --------------------------------- **Branch:** Networking Architecture where clients request services and servers provide them Command Line Interface (CLI) --------------------------------- **Branch:** Command Line & Shell A text-based interface for giving commands to the OS Configuration File --------------------------------- **Branch:** Server Configuration Management A text file that controls how a program or service behaves, often found in /etc Configuration Management --------------------------------- **Branch:** Server Configuration Management Keeping server settings consistent, documented and reproducible Container --------------------------------- **Branch:** Virtualization A lightweight isolated environment that shares the host kernel, such as Docker Context Switch --------------------------------- **Branch:** Process Management Saving one process's state and loading another's so the CPU can switch between them Converter / Adapter --------------------------------- **Branch:** Django ORM Functions that translate values coming out of the database into Python types / Python values going in into database types CPU Scheduling --------------------------------- **Branch:** Process Management How the OS decides which ready process runs next on the CPU Cron Job --------------------------------- **Branch:** Command Line & Shell A task scheduled to run automatically at set times :ref:`Back to top ` .. _glossary-d: D ================================= Daemon / Service --------------------------------- **Branch:** OS Overview & Components A background process that runs continuously to provide a service, such as a web server Database Backend --------------------------------- **Branch:** Django ORM The part of Django that knows one specific database's SQL dialect, types and connection details, such as django.db.backends.sqlite3 Database Index --------------------------------- **Branch:** Databases A sorted lookup structure that lets the database find rows without reading the whole table Database is Locked Error --------------------------------- **Branch:** SQLite Internals SQLite's error when a connection waits too long for another connection to finish writing Database Page --------------------------------- **Branch:** SQLite Internals The fixed-size block (4096 bytes by default) that SQLite reads and writes; the file is a list of pages Database Server --------------------------------- **Branch:** Servers & Services A service that stores and manages data for applications, such as MySQL Deadlock --------------------------------- **Branch:** Process Management A state where processes wait forever on resources held by each other Default Deny Policy --------------------------------- **Branch:** Security Firewall setup that blocks all incoming traffic unless a rule allows it Descriptor --------------------------------- **Branch:** Django ORM A Python object with a __get__ method that runs code when an attribute is read; Django uses them for relationships like screen.season Device Driver --------------------------------- **Branch:** OS Overview & Components Kernel code that lets the OS communicate with a specific hardware device df / free --------------------------------- **Branch:** Services & Logs Shows remaining disk space / shows memory use dig / nslookup --------------------------------- **Branch:** Networking Command-line tools that ask DNS directly which records a name returns Directory Hierarchy --------------------------------- **Branch:** File Systems & Storage The tree structure of folders starting at the root directory / Directory Permissions (r/w/x on folders) ---------------------------------------- **Branch:** Permissions Gives permissions for a folder, r=read, w=add or remove files, x=enter folder Distribution (Distro) --------------------------------- **Branch:** OS Options A packaged OS built on the Linux kernel with its own tools and package manager, such as Ubuntu or Debian Django Model --------------------------------- **Branch:** Django ORM A Python class in models.py that describes one database table; each instance is one row django_migrations Table --------------------------------- **Branch:** Django ORM The table where Django records which migrations have already been applied to a database DNS (Domain Name System) --------------------------------- **Branch:** Domain Management & Encryption The system that translates domain names into IP addresses DNS Propagation --------------------------------- **Branch:** Domain Management & Encryption The delay before a DNS change is seen everywhere, because DNS servers keep old answers until their TTL runs out DNS Record (A / CNAME) --------------------------------- **Branch:** Domain Management & Encryption Entries that map a domain to an IP address (A) or to another name (CNAME) DNS Resolver --------------------------------- **Branch:** Domain Management & Encryption The server, often run by your internet provider, that looks up domain names for your computer and caches the answers DNS Zone --------------------------------- **Branch:** Domain Management & Encryption The full set of DNS records for one domain, edited in the registrar's or DNS host's settings Domain Name --------------------------------- **Branch:** Domain Management & Encryption A human-readable name, such as supersims21.org, that points to a server's IP address; rented from a registrar by the year Domain Registrar --------------------------------- **Branch:** Domain Management & Encryption A company that manages the registration of domain names :ref:`Back to top ` .. _glossary-e: E ================================= Embedded Database --------------------------------- **Branch:** SQLite Internals A database engine that runs as a library inside the application's own process instead of as a separate server Enabled vs Active (enable vs start) ----------------------------------- **Branch:** Services & Logs Service starts automatically / Is running currently Environment Variable --------------------------------- **Branch:** Command Line & Shell A named value available to processes that affects how they behave, such as PATH /etc/passwd, /etc/shadow, /etc/group ------------------------------------ **Branch:** User Management Plain text files where Linux lists user accounts, holds password hashes, or lists groups /etc/hosts --------------------------------- **Branch:** Networking A local file that maps names to IP addresses on one computer and is checked before DNS Exit Status --------------------------------- **Branch:** Command Line & Shell A number a command returns when it finishes; 0 means success :ref:`Back to top ` .. _glossary-f: F ================================= F Expression --------------------------------- **Branch:** Django ORM A reference to a column's current value inside the database so math like revealed + 1 runs in SQL Fail2ban --------------------------------- **Branch:** Security Tool that bans IP addresses showing signs of malicious login attempts Fail2ban Jail (jail.local) --------------------------------- **Branch:** Security Ruleset that sets the number of failed logins and how long an address is banned Field Lookup (__) --------------------------------- **Branch:** Django ORM The double-underscore syntax, such as name__icontains, that tells Django which SQL comparison to use on a field File Lock (fcntl) --------------------------------- **Branch:** SQLite Internals An operating system lock on part of a file that SQLite uses so only one connection writes at a time File Permissions (rwx) --------------------------------- **Branch:** Permissions Read, write and execute rights set separately for the owner, group and others File System --------------------------------- **Branch:** File Systems & Storage The method the OS uses to organize and store files on a disk, such as ext4 or NTFS Firewall --------------------------------- **Branch:** Security Software or hardware that allows or blocks network traffic based on rules ForeignKey --------------------------------- **Branch:** Django ORM A field that links a row to a row in another table by storing that row's primary key, such as season_id Full / Incremental / Differential Backup ---------------------------------------- **Branch:** Backup & Recovery Backing up all data, only changes since the last backup, or all changes since the last full backup Full Stack Server (LAMP) --------------------------------- **Branch:** Servers & Services A server running the full software stack: Linux, Apache, MySQL/MariaDB and PHP :ref:`Back to top ` .. _glossary-g: G ================================= Git Server --------------------------------- **Branch:** Servers & Services A server that hosts git repositories for version control Group --------------------------------- **Branch:** User Management A collection of users that can share permissions on files and resources :ref:`Back to top ` .. _glossary-h: H ================================= .htaccess --------------------------------- **Branch:** Permissions A per-directory Apache config file used to control web user access, such as password protection HTTPS --------------------------------- **Branch:** Domain Management & Encryption HTTP secured with TLS encryption Hypervisor --------------------------------- **Branch:** Virtualization Software that creates and runs virtual machines and divides hardware among them :ref:`Back to top ` .. _glossary-i: I ================================= ICMP --------------------------------- **Branch:** Networking The protocol ping uses; many servers and cloud firewalls block it for security Immutable Backup --------------------------------- **Branch:** Backup & Recovery A backup that cannot be changed or deleted for a set period Infrastructure as Code --------------------------------- **Branch:** Server Configuration Management Defining server setup in files that can be version controlled and rerun init / systemd --------------------------------- **Branch:** OS Overview & Components The first process started by the kernel; it starts and manages all other services Inode --------------------------------- **Branch:** File Systems & Storage A data structure storing a file's metadata such as owner, permissions and disk location Interrupt --------------------------------- **Branch:** OS Overview & Components A signal from hardware or software that makes the CPU pause and handle an event IP Address --------------------------------- **Branch:** Networking A numeric address that identifies a device on a network IPv4 / IPv6 --------------------------------- **Branch:** Networking 32-bit addresses written as four numbers like 213.0.0.1 / 128-bit addresses written in hexadecimal like 2001:db8::1 :ref:`Back to top ` .. _glossary-j: J ================================= journald / journalctl --------------------------------- **Branch:** Services & Logs Systemd service that collects all other service info / command for reading that log JSON Functions (JSON1) --------------------------------- **Branch:** SQLite Internals SQLite's built-in functions like JSON_VALID and JSON_EXTRACT that Django uses for JSONField :ref:`Back to top ` .. _glossary-k: K ================================= Kernel --------------------------------- **Branch:** OS Overview & Components The core of the OS that runs with full hardware privileges and manages CPU, memory and devices :ref:`Back to top ` .. _glossary-l: L ================================= Lazy Evaluation --------------------------------- **Branch:** Django ORM Waiting to do work until the result is actually needed; a QuerySet runs no SQL until it is looped over, printed or counted Load Balancing --------------------------------- **Branch:** Servers & Services Spreading incoming requests across several servers to share the work Log File --------------------------------- **Branch:** Security A record of system events used for troubleshooting and security auditing LTS (Long Term Support) --------------------------------- **Branch:** OS Options An OS release that receives security and bug fixes for an extended period :ref:`Back to top ` .. _glossary-m: M ================================= makemigrations / migrate --------------------------------- **Branch:** Django ORM Commands that write migration files by comparing models to past migrations / apply unapplied migrations to the database Manager (objects) --------------------------------- **Branch:** Django ORM The interface on a model class, usually named objects, that starts every database query _meta (Model Options) --------------------------------- **Branch:** Django ORM The object Django attaches to every model that describes its table: fields, table name, ordering and constraints Metaclass (ModelBase) --------------------------------- **Branch:** Django ORM The class of a class; Django's ModelBase rebuilds each model class when it is defined to add _meta, objects, the id field and relationships MFA (Multi-Factor Authentication) --------------------------------- **Branch:** User Management A login that needs a second proof of identification Migration --------------------------------- **Branch:** Django ORM A Python file that records a change to the database schema so it can be applied to any copy of the database Model Field --------------------------------- **Branch:** Django ORM A class attribute on a model, such as CharField or JSONField, that describes one column and how to convert its values Monolithic Kernel vs Microkernel --------------------------------- **Branch:** OS Overview & Components Kernel designs that either run all services in kernel space or keep only essentials there Mounting --------------------------------- **Branch:** File Systems & Storage Attaching a storage device or partition to a point in the directory tree Mutex / Semaphore --------------------------------- **Branch:** Process Management Synchronization tools that control access to shared resources by concurrent processes MX Record --------------------------------- **Branch:** Domain Management & Encryption A DNS record that names the mail server that receives email for a domain :ref:`Back to top ` .. _glossary-n: N ================================= N+1 Query Problem --------------------------------- **Branch:** Django ORM A slowdown where code runs 1 query for a list and then 1 more query for every item in it Nameserver (NS Record) --------------------------------- **Branch:** Domain Management & Encryption The server that holds the official DNS records for a domain; the registrar tells the internet which nameservers to ask nano --------------------------------- **Branch:** Editors A simple beginner-friendly terminal text editor netfilter / nftables --------------------------------- **Branch:** Security The packet filter that allows/blocks network traffic / the rule system it uses Notepad++ --------------------------------- **Branch:** Editors A graphical Windows source code editor with syntax highlighting NTP / timesyncd --------------------------------- **Branch:** Services & Logs How computers keep their clocks correct across the internet Numeric (Octal) Permissions --------------------------------- **Branch:** Permissions The 3 digit permissions (rwx) :ref:`Back to top ` .. _glossary-o: O ================================= Object-Relational Mapper (ORM) --------------------------------- **Branch:** Django ORM A library that maps database tables to classes and rows to objects so you can work with data in code instead of SQL Offline / Air-Gapped Backup --------------------------------- **Branch:** Backup & Recovery A backup disconnected from the network so ransomware cannot reach it on_delete (CASCADE / SET_NULL) --------------------------------- **Branch:** Django ORM Rule for what happens to linked rows when a row is deleted: delete them too / set their foreign key to NULL; Django carries it out in Python Open Source vs Proprietary --------------------------------- **Branch:** OS Options Whether the OS source code is freely available and modifiable or owned and restricted by a vendor Operating System --------------------------------- **Branch:** OS Overview & Components Software that manages hardware resources and provides common services to programs and users Overflow Page --------------------------------- **Branch:** SQLite Internals An extra page that holds the part of a row that is too large to fit on its B-tree page :ref:`Back to top ` .. _glossary-p: P ================================= Package Manager --------------------------------- **Branch:** OS Options Tool that installs, updates and removes software along with its dependencies, such as apt Packet Loss --------------------------------- **Branch:** Networking The percentage of sent packets that got no reply; 100% loss on ping can mean ICMP is blocked, not that DNS failed or the server is down Paging --------------------------------- **Branch:** Memory Management Dividing memory into fixed-size pages that map virtual addresses to physical frames Parameterized Query --------------------------------- **Branch:** Databases SQL sent with placeholders (? or %s) and values passed separately so the values can never change the SQL Partition --------------------------------- **Branch:** File Systems & Storage A separately managed section of a storage device Patch / Update --------------------------------- **Branch:** Security Software changes that fix bugs and security vulnerabilities Persistent Journal --------------------------------- **Branch:** Services & Logs Keeps the system log so it survives with a reboot Ping --------------------------------- **Branch:** Networking Sends "echo request" packets and receives "echo reply" packets, used to check if a machine is up, reachable, and connection speed Pipe --------------------------------- **Branch:** Command Line & Shell The | operator that sends one command's output as input to another Port --------------------------------- **Branch:** Networking A number that identifies a specific service on a host, such as 80 for HTTP or 22 for SSH PRAGMA --------------------------------- **Branch:** SQLite Internals A SQLite command that reads or changes database settings, such as PRAGMA foreign_keys = ON Primary Key --------------------------------- **Branch:** Databases A column that uniquely identifies each row in a table, such as id Principle of Least Privilege --------------------------------- **Branch:** Permissions Giving users and programs only the access they need to do their job Process --------------------------------- **Branch:** Process Management A program in execution with its own memory space and resources Process ID (PID) --------------------------------- **Branch:** Process Management A unique number the OS assigns to identify each running process Process States --------------------------------- **Branch:** Process Management The stages a process moves through: new, ready, running, waiting and terminated Public / Private Key --------------------------------- **Branch:** Domain Management & Encryption A key pair used in asymmetric encryption; the public key encrypts and the private key decrypts :ref:`Back to top ` .. _glossary-q: Q ================================= Query Plan (EXPLAIN QUERY PLAN) --------------------------------- **Branch:** SQLite Internals The steps SQLite will use to run a query; SEARCH means an index is used and SCAN means every row is read QuerySet --------------------------------- **Branch:** Django ORM A lazy, chainable description of a database query that only runs its SQL when its data is needed :ref:`Back to top ` .. _glossary-r: R ================================= Race Condition --------------------------------- **Branch:** Process Management A bug where the result depends on the unpredictable timing of concurrent processes Ransomware --------------------------------- **Branch:** Security Malware that encrypts a victim's data and demands payment to unlock it Reboot Required (kernel updates) --------------------------------- **Branch:** Security Some updates need the server to restart before they take effect Recovery Point / Time Objective (RPO / RTO) ------------------------------------------- **Branch:** Backup & Recovery How much data loss is acceptable and how quickly a system must be restored Redirection --------------------------------- **Branch:** Command Line & Shell Sending a command's input or output to or from a file using > < or >> related_name --------------------------------- **Branch:** Django ORM The name of the reverse attribute Django adds to the other model, such as season.screens RETURNING Clause --------------------------------- **Branch:** SQLite Internals SQL that sends back values from rows just inserted or updated, such as the new id, in the same statement Reverse DNS (PTR Record) --------------------------------- **Branch:** Domain Management & Encryption A lookup that goes the other way, turning an IP address back into a domain name Reverse Proxy --------------------------------- **Branch:** Servers & Services A server that receives client requests and forwards them to back-end servers Rollback Journal --------------------------------- **Branch:** SQLite Internals A file (db.sqlite3-journal) holding original copies of pages so an interrupted write can be undone Root / Superuser --------------------------------- **Branch:** User Management The administrator account with unrestricted access to the system Rowid --------------------------------- **Branch:** SQLite Internals The hidden 64-bit integer key of every SQLite table row; an INTEGER PRIMARY KEY column becomes an alias for it rsync --------------------------------- **Branch:** Backup & Recovery A tool that efficiently copies and syncs files between locations :ref:`Back to top ` .. _glossary-s: S ================================= Savepoint --------------------------------- **Branch:** Databases A marker inside a transaction that lets you roll back part of the work without cancelling the whole transaction Schema Editor --------------------------------- **Branch:** Django ORM The Django component that turns migration operations into CREATE TABLE, ALTER TABLE and CREATE INDEX statements select_related / prefetch_related --------------------------------- **Branch:** Django ORM Ways to load related objects ahead of time with a SQL JOIN / with a second query using IN (...) Setgid Bit --------------------------------- **Branch:** Permissions A permission folder that makes all new files belong to the folder's group Shebang --------------------------------- **Branch:** Command Line & Shell The first line of a script (#!/bin/bash) that names the interpreter to run it Shell --------------------------------- **Branch:** OS Overview & Components A program that interprets user commands and passes them to the OS Signal --------------------------------- **Branch:** Process Management A notification sent to a process to trigger an action, such as SIGKILL to stop it Snapshot --------------------------------- **Branch:** Backup & Recovery A point-in-time copy of a system or file system SQL Compiler --------------------------------- **Branch:** Django ORM The Django component that turns a Query tree into an SQL string and a separate list of parameters SQL Injection --------------------------------- **Branch:** Databases An attack where user input is pasted into SQL text and changes what the query does SQLite --------------------------------- **Branch:** SQLite Internals A small, serverless, embedded SQL database engine that stores a whole database in one ordinary file sqlite3 Module (DB-API) --------------------------------- **Branch:** SQLite Internals Python's built-in driver for SQLite, which follows the standard Python database API (PEP 249) sqlite_master (sqlite_schema) --------------------------------- **Branch:** SQLite Internals SQLite's built-in table that stores the CREATE statement and root page of every table and index SSH (Secure Shell) --------------------------------- **Branch:** Networking An encrypted protocol for logging into and running commands on a remote server SSH Hardening (PermitRootLogin / PasswordAuthentication) -------------------------------------------------------- **Branch:** User Management Making logins safer by blocking logging in from root and allowing keys instead of password login SSH Key Authentication --------------------------------- **Branch:** User Management Logging in with a pair of keys (public and private) instead of a password SSL/TLS --------------------------------- **Branch:** Domain Management & Encryption Protocols that encrypt data sent between a client and a server Standard Input/Output/Error --------------------------------- **Branch:** Command Line & Shell The three default data streams (stdin, stdout, stderr) every process has Subdomain --------------------------------- **Branch:** Domain Management & Encryption A name in front of the domain, such as www.supersims21.org, that can point to its own address sudo --------------------------------- **Branch:** User Management Command that lets an authorized user run a command with root privileges Swap Space --------------------------------- **Branch:** Memory Management Disk space used to hold memory pages when physical RAM is full Symbolic Link --------------------------------- **Branch:** File Systems & Storage A special file that points to another file or directory System Call --------------------------------- **Branch:** OS Overview & Components The interface a program uses to request a service from the kernel, such as reading a file systemctl --------------------------------- **Branch:** Services & Logs Manages services through systemd :ref:`Back to top ` .. _glossary-t: T ================================= Table Remake --------------------------------- **Branch:** Django ORM Django's workaround for SQLite's limited ALTER TABLE: create a new table, copy the rows, drop the old table and rename the new one Terminal --------------------------------- **Branch:** Command Line & Shell The program window that provides access to a shell Thread --------------------------------- **Branch:** Process Management The smallest unit of execution within a process; threads share the process's memory Top-Level Domain (TLD) --------------------------------- **Branch:** Domain Management & Encryption The ending of a domain name, such as .com, .org or .ai; each ending has its own yearly price Transaction --------------------------------- **Branch:** Databases A group of database operations that succeed or fail together as one unit transaction.atomic --------------------------------- **Branch:** Django ORM Django's way to group database statements so they all succeed or all get rolled back TTL (Time To Live) --------------------------------- **Branch:** Domain Management & Encryption How long other computers may remember (cache) a DNS answer before asking again TXT Record --------------------------------- **Branch:** Domain Management & Encryption A DNS record that holds text, often used to prove you own a domain or to set email security rules Type Affinity --------------------------------- **Branch:** SQLite Internals SQLite's per-column type preference; the value itself carries the real type, so varchar(100) does not limit length :ref:`Back to top ` .. _glossary-u: U ================================= UFW / iptables --------------------------------- **Branch:** Security Linux tools used to define firewall rules UID / GID --------------------------------- **Branch:** User Management Numeric user and group IDs the OS uses internally to identify accounts unattended-upgrades --------------------------------- **Branch:** Security Debian tool that checks security fixes everyday and installs them automatically Unique Constraint --------------------------------- **Branch:** Databases A rule that no two rows may have the same value or combination of values in certain columns Unit File --------------------------------- **Branch:** Services & Logs Configuration file that tells systemd how to run a service User Account --------------------------------- **Branch:** User Management An identity the OS uses to track who owns files and runs processes User Mode vs Kernel Mode --------------------------------- **Branch:** OS Overview & Components CPU privilege levels that separate restricted application code from privileged OS code :ref:`Back to top ` .. _glossary-v: V ================================= VDBE (Virtual Database Engine) --------------------------------- **Branch:** SQLite Internals SQLite's virtual machine that runs SQL after it has been compiled into bytecode Version Control --------------------------------- **Branch:** Servers & Services Tracking and managing changes to files over time vi / vim --------------------------------- **Branch:** Editors A modal text editor found on nearly all Unix systems, with separate insert and command modes Virtual Host --------------------------------- **Branch:** Servers & Services Configuration that lets one web server host multiple websites Virtual Machine (VM) --------------------------------- **Branch:** Virtualization A software-emulated computer that runs its own OS on top of a host system Virtual Memory --------------------------------- **Branch:** Memory Management Technique that gives each process its own address space larger than physical RAM VNC Console --------------------------------- **Branch:** User Management Your emergency way back into the system :ref:`Back to top ` .. _glossary-w: W ================================= WAL (Write-Ahead Logging) --------------------------------- **Branch:** SQLite Internals A SQLite mode where changes are added to a separate -wal file so readers and a writer can work at the same time Web Server --------------------------------- **Branch:** Servers & Services Software that serves web pages to clients over HTTP, such as Apache2 or Nginx WHOIS --------------------------------- **Branch:** Domain Management & Encryption A public lookup that shows a domain's registrar, expiration date and nameservers Wiki --------------------------------- **Branch:** Servers & Services A web application that lets users collaboratively create and edit pages, such as MediaWiki :ref:`Back to top `