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	apt command dpkg command Linux commands cheat sheet

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.

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

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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