apt-cache Command in Linux: Search, Policy & Dependencies (Ubuntu/Debian)

Jan 2, 2022 Jul 1, 2026 Rohan Timalsina Deepak Prasad

Tested on	Ubuntu 25.04 (Plucky Puffin)
Package	`apt 3.0.0`
Applies to	Ubuntu, Debian, Kali Linux, Linux Mint, Pop!_OS, Raspberry Pi OS, elementary OS, Zorin OS, Parrot OS, MX Linux
Privilege	read-only (no elevated privileges)
Man page	apt-cache(8)
Scope	Read-only APT index queries: search, metadata, policy, and forward or reverse dependencies without network access after apt update.
Related guides	dpkg command Linux commands cheat sheet

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apt-cache — quick reference

Search and list

Find package names in the local index — no root required.

When to use	Command
Search names and descriptions for a keyword	`apt-cache search pattern`
Search package names only	`apt-cache search --names-only pattern`
List package names matching a prefix	`apt-cache pkgnames prefix`

Package records

When to use	Command
Show readable metadata (version, depends, size)	`apt-cache show package_name`
Show versions, reverse depends, and file mapping	`apt-cache showpkg package_name`
Show installed vs candidate version and pin priority	`apt-cache policy package_name`
List available versions from all sources	`apt-cache madison package_name`

Dependencies

When to use	Command
Show packages this package depends on	`apt-cache depends package_name`
Show packages that depend on this package	`apt-cache rdepends package_name`
Walk the dependency tree recursively	`apt-cache depends --recurse package_name`
Limit depends output to important packages	`apt-cache depends --important package_name`

Diagnostics

When to use	Command
List packages with unmet dependencies in the cache	`apt-cache unmet`

Help and version

When to use	Command
Show built-in usage summary	`apt-cache --help`
Print apt version (apt-cache ships with apt)	`apt-cache --version`

apt-cache — command syntax

apt-cache queries data under /var/lib/apt/lists/ populated by apt update. Synopsis from apt-cache --help on Ubuntu 25.04 (apt 3.0.0):

text
apt-cache [options] command
       apt-cache [options] show pkg1 [pkg2 ...]

Most used commands:
  showsrc - Show source records
  search - Search the package list for a regex pattern
  depends - Show raw dependency information for a package
  rdepends - Show reverse dependency information for a package
  show - Show a readable record for the package
  pkgnames - List the names of all packages in the system
  policy - Show policy settings

apt-cache does not install or remove packages. Refresh the index with sudo apt update when you need the newest repository data.

apt-cache — command examples

Essential Search the local package index

Find the exact package name before install — works offline against the last apt update.

Run the command:

bash

apt-cache search --names-only '^curl$'

Sample output:

The example below transfers data with curl over HTTP(S); the curl command is a quick reference for flags and syntax.

output

curl - command line tool for transferring data with URL syntax

Omit --names-only to match descriptions too (more results, slower to scan).

Essential See installed vs candidate version

policy explains which version apt prefers and why — essential when upgrades stall or multiple repos supply the same name.

Run the command:

bash

apt-cache policy curl

Sample output:

output

curl:
  Installed: 8.12.1-3ubuntu1
  Candidate: 8.12.1-3ubuntu1
  Version table:
 *** 8.12.1-3ubuntu1 1001
       1001 http://archive.ubuntu.com/ubuntu plucky/main amd64 Packages
        100 /var/lib/dpkg/status

The *** marks the version apt would install. Priority 1001 beats plain 500 from a standard mirror. The same policy check confirms an uninstall stuck Installed: (none) after apt purge—see how to remove software on Ubuntu. It also compares Ubuntu’s packaged HPLIP branch with what your printer needs—see install HPLIP on Ubuntu before you switch to HP’s manual .run installer. For imagemagick, Candidate shows ImageMagick 7 on 26.04 (7.1.x) vs ImageMagick 6 on 24.04 (6.9.x)—see How to Install ImageMagick 7 on Ubuntu 26.04 or How to Install ImageMagick on Ubuntu 24.04 & 22.04.

Essential Read full package metadata with show

show prints the same fields administrators skim before approving an install.

Run the command:

bash

apt-cache show curl | head -12

Sample output:

output

Package: curl
Architecture: amd64
Version: 8.12.1-3ubuntu1
Multi-Arch: foreign
Priority: optional
Section: web
Origin: Ubuntu
Maintainer: Ubuntu Developers <ubuntu-devel-discuss@lists.ubuntu.com>
Original-Maintainer: Debian Curl Maintainers <team+curl@tracker.debian.org>
Bugs: https://bugs.launchpad.net/ubuntu/+filebug
Installed-Size: 491
Depends: libc6 (>= 2.38), libcurl4t64 (= 8.12.1-3ubuntu1), zlib1g (>= 1:1.1.4)

Compare with apt show curl — similar fields, different formatter.

Common List forward dependencies

Know what libraries a package pulls before installing on a minimal system.

Run the command:

bash

apt-cache depends curl | head -6

Sample output:

output

curl
  Depends: libc6
  Depends: libcurl4t64
  Depends: zlib1g

Add --recurse for the full tree (can be long on desktop metapackages).

Common Find reverse dependencies before removal

See which installed packages would break if you remove a library.

Run the command:

bash

apt-cache rdepends curl | head -8

Sample output:

output

curl
Reverse Depends:
  debian-goodies
  zfs-test
  mariadb-plugin-connect
  libsoup2.4-tests
  libsoup-3.0-tests
  djvulibre-bin

Not every listed package is installed — cross-check with dpkg -l or apt list --installed.

Common List names matching a prefix

Quick autocomplete-style listing when you know the first letters of a package family.

Run the command:

bash

apt-cache pkgnames curl | head -5

Sample output:

output

curl
curlftpfs

Useful in scripts that enumerate related packages.

Advanced Debug versions with showpkg

showpkg exposes cache file paths, MD5 sums, and reverse-depends — handy when mirroring or debugging stale indexes.

Run the command:

bash

apt-cache showpkg curl | head -14

Sample output:

output

Package: curl
Versions: 
8.12.1-3ubuntu1 (/var/lib/apt/lists/archive.ubuntu.com_ubuntu_dists_plucky_main_binary-amd64_Packages) (/var/lib/dpkg/status)
 Description Language: 
                 File: /var/lib/apt/lists/archive.ubuntu.com_ubuntu_dists_plucky_main_binary-amd64_Packages
                  MD5: f83293d10df083ae6f7bb7d01642913c
 Description Language: en
                 File: /var/lib/apt/lists/archive.ubuntu.com_ubuntu_dists_plucky_main_i18n_Translation-en
                  MD5: f83293d10df083ae6f7bb7d01642913c

Reverse Depends:

When MD5s disagree across list files, run sudo apt update.

Advanced Compare repo versions with madison

madison lists every indexed version and the repository that provides it — similar to apt list -a.

Run the command:

bash

apt-cache madison curl

Sample output:

output

      curl | 8.12.1-3ubuntu1 | http://archive.ubuntu.com/ubuntu plucky/main amd64 Packages

Multiple rows appear when PPAs or security pockets ship alternate versions.

apt-cache — when to use / when not

Use apt-cache when	Use something else when
You need read-only metadata from the local APT cache	You are installing or removing — apt
You are offline but the index was updated recently	You need fresh mirror data — `sudo apt update` first
You debug pinning, policy, or dependencies	You want friendly search output — `apt search` / `apt show`
You script exact cache queries in maintenance tools	You query installed files only — `dpkg -L` / `dpkg -S`

apt-cache vs apt search

	apt-cache	apt search / apt show
Privilege	User (read-only)	User for search/show
Output style	Dense, script-oriented	Colored, paginated lists
Policy / madison / showpkg	Native subcommands	Not available
Typical use	Diagnostics and automation	Interactive admin

Many admins use apt for daily search and apt-cache for policy, madison, and rdepends.

apt-cache — interview corner

What does apt-cache do?

apt-cache queries the local APT package index built by apt update. It searches names, prints metadata, shows policy priorities, and lists dependencies — without installing anything and without network once lists are cached.

A strong answer is:

"apt-cache is read-only metadata from /var/lib/apt/lists — search, show, policy, depends, and rdepends offline after an update."

Do you need sudo for apt-cache?

No. apt-cache never modifies the system. Any user who can read /var/lib/apt/lists/ can run apt-cache search, policy, and depends.

Installing packages still requires sudo through apt or apt-get.

A strong answer is:

"apt-cache is read-only — no sudo. I use it as a regular user to inspect packages before escalating for install."

What does apt-cache policy show?

For each package name, policy prints:

Installed version on disk
Candidate version apt would install next
Version table — each available version, its pin priority, and source URI

High-priority pins (for example 1001 from security pockets) beat lower-priority mirrors.

A strong answer is:

"policy shows installed vs candidate and the pin priority table — I use it when apt won't upgrade or multiple repos conflict."

What is the difference between depends and rdepends?

Command	Direction
`apt-cache depends pkg`	What pkg needs (forward dependencies)
`apt-cache rdepends pkg`	What needs pkg (reverse dependencies)

Run rdepends before removing shared libraries to see potential breakage.

A strong answer is:

"depends is what the package requires; rdepends is who requires the package — critical before removals."

Why can apt-cache show outdated information?

apt-cache only reads cached list files. If nobody ran apt update recently, Candidate versions may lag behind the mirror.

Fix: sudo apt update, then re-run apt-cache policy.

A strong answer is:

"It reads the local index only — stale until apt update. I refresh lists before trusting candidate versions."

Troubleshooting

Symptom	Likely cause	Fix
Empty `search` results	Stale or minimal index	`sudo apt update`
`Package has no installation candidate`	Not in enabled repos	Check `apt-cache policy`; edit sources
`policy` shows only installed line	Package not in any list file	Enable component (`universe`, etc.) and update
`rdepends` lists hundreds of names	Metapackage or popular library	Filter with `grep`; verify with `dpkg -l`
`showsrc` errors about deb-src	No source repositories enabled	Add `deb-src` URIs to sources; use `apt-cache show` for binary metadata
Differs from `apt show`	Formatter only	Compare `Version` and `Depends` fields

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Rohan Timalsina

is a technical writer and Linux enthusiast who writes practical guides on Linux commands and system administration. He focuses on simplifying complex topics through clear explanations.

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