List of Commands for Package Dependency Checking in Ubuntu

Every new user will experience dealing with package dependency in Ubuntu. This list is a shortcut to help you get what dependencies you want in faster way. You can choose any command you need from below. We list variety of 5 commands here dpkg, dpkg-deb, apt-rdepends, apt-cache, and apt-get. We use Ubuntu 12.04 32 bit for this article. If you are looking for package dependency searching in Ubuntu then this article is for you.

Prerequisites

1. You must install apt-rdepends first because it is not built-in included in Ubuntu. Install it with sudo apt-get install rdepends. 
2. You must at least ever once doing sudo apt-get update. It needs internet access. It builds complete APT Database for your Ubuntu. If you have no APT Database, no command apt-cache, apt-rdepends, or apt-get can be performed completely.

About APT Cache Terminology

In simplified words, APT Cache is a term to explain both APT Database and APT Package Files. APT Database is stored at /var/lib/apt/lists/. It contains plain text files stored from sudo apt-get update a user performs. APT Package Files are stored in /var/cache/apt/archives/. It contains DEB files stored from any sudo apt-get install command a user performs. apt-cache command works for these two types of cache.

1. dpkg: Show Package Information

2. dpkg-deb: Extracting DEB Package 

Synopsis: dpkg-deb --raw-extract <package> <directory>
Example: dpkg-deb --raw-extract uget_1.8.0-1_i386.deb /tmp
The dependencies information shows up after Depends flag. So, the dependencies of this uget package are libc6 (>= 2.4), libcairo2 (>= 1.2.4), libcurl3 (>= 7.16.2-1), libglib2.0-0 (>= 2.20.0), libgstreamer0.10-0 (>= 0.10.0), libgtk2.0-0 (>= 2.24.0), libnotify4 (>= 0.7.0), libpango1.0-0 (>= 1.14.0).

3. dpkg-deb: Show Depends Field Contents of A Package Directly

Synopsis: dpkg-deb --field <package> <field>
Example: dpkg-deb --field uget_1.8.0-1_i386.deb Depends
Output: libc6 (>= 2.4), libcairo2 (>= 1.2.4), libcurl3 (>= 7.16.2-1), libglib2.0-0 (>= 2.20.0), libgstreamer0.10-0 (>= 0.10.0), libgtk2.0-0 (>= 2.24.0), libnotify4 (>= 0.7.0), libpango1.0-0 (>= 1.14.0)

This command sums up what 2nd command above did, into just one single step. This command pulls directly Depends field from control file inside the DEBIAN directory. For frequent working with package, this command is more suitable than the previous. We see the output is exactly the same.

4. apt-cache: Show Package Information

Synopsis: apt-cache show <package>
Example: apt-cache show uget

This command shows up control file content inside a package that are already inside APT database. You must override <package> field with package name, not file name. It is similar with dpkg -I command above except apt-cache show will take information from APT Database not from a single DEB file.

5. apt-cache: Show Package More Information

Synopsis: apt-cache showpkg <package>
Example: apt-cache showpkg uget

This command shows up detailed information similar with show command before. But showpkg shows where a package belongs to in APT Database. Especially in which database file it belongs. The output will be like this.

Package: uget
Versions: 
2.0-0ubuntu0~precise (/var/lib/apt/lists/ppa.launchpad.net_plushuang-tw_uget-stable_ubuntu_dists_precise_main_binary-i386_Packages)
 Description Language: 
                 File: /var/lib/apt/lists/ppa.launchpad.net_plushuang-tw_uget-stable_ubuntu_dists_precise_main_binary-i386_Packages
                  MD5: df1c64f6fd949d38e1bd89de60a8af32
 Description Language: en
                 File: /var/lib/apt/lists/ppa.launchpad.net_plushuang-tw_uget-stable_ubuntu_dists_precise_main_i18n_Translation-en
                  MD5: df1c64f6fd949d38e1bd89de60a8af32

6. apt-rdepends: Show Complete Dependencies Recursively

Synopsis: apt-rdepends <package>
Example: apt-rdepends nano

This command will track and show complete dependencies list of a package. This will list dependencies recursively so it will produce very long output. This command includes whole dependencies, it doesn't exclude installed dependencies. For the sake of output simplicity, we use nano instead of uget as example. Output below are exactly all dependencies of nano package in our Ubuntu 12.04.

Reading package lists... Done
Building dependency tree       
Reading state information... Done
nano
  Depends: dpkg (>= 1.15.4)
  Depends: install-info
  Depends: libc6 (>= 2.11)
  Depends: libncursesw5 (>= 5.7+20100313)
dpkg
  PreDepends: coreutils (>= 5.93-1)
  PreDepends: libbz2-1.0
  PreDepends: libc6 (>= 2.11)
  PreDepends: libselinux1 (>= 1.32)
  PreDepends: tar (>= 1.23)
  PreDepends: xz-utils
  PreDepends: zlib1g (>= 1:1.1.4)
coreutils
  Depends: dpkg (>= 1.15.4)
  Depends: install-info
  PreDepends: libacl1 (>= 2.2.51-5)
  PreDepends: libattr1 (>= 1:2.4.46-5)
  PreDepends: libc6 (>= 2.15)
  PreDepends: libselinux1 (>= 1.32)
install-info
  Depends: libc6 (>= 2.4)
libc6
  Depends: libc-bin (= 2.15-0ubuntu10)
  Depends: libgcc1
  Depends: tzdata
libc-bin
libgcc1
  Depends: gcc-4.6-base (= 4.6.3-1ubuntu5)
  Depends: libc6 (>= 2.2.4)
  PreDepends: multiarch-support
gcc-4.6-base
multiarch-support
  Depends: libc6 (>= 2.13-0ubuntu6)
tzdata
  Depends: debconf (>= 0.5)
  Depends: debconf-2.0
debconf
  PreDepends: perl-base (>= 5.6.1-4)
perl-base
  PreDepends: dpkg (>= 1.14.20)
  PreDepends: libc6 (>= 2.11)
debconf-2.0
libacl1
  Depends: libattr1 (>= 2.4.46-3)
  Depends: libc6 (>= 2.4)
  PreDepends: multiarch-support
libattr1
  Depends: libc6 (>= 2.4)
  PreDepends: multiarch-support
libselinux1
  Depends: libc6 (>= 2.8)
  PreDepends: multiarch-support
libbz2-1.0
  Depends: libc6 (>= 2.4)
  PreDepends: multiarch-support
tar
  PreDepends: libc6 (>= 2.8)
xz-utils
  Depends: libc6 (>= 2.7)
  Depends: liblzma5 (>= 5.1.1alpha+20110809)
liblzma5
  Depends: libc6 (>= 2.4)
  PreDepends: multiarch-support
zlib1g
  Depends: libc6 (>= 2.4)
  PreDepends: multiarch-support
libncursesw5
  Depends: libc6 (>= 2.4)
  Depends: libtinfo5 (= 5.9-4)
  PreDepends: multiarch-support
libtinfo5
  Depends: libc6 (>= 2.4)
  PreDepends: multiarch-support

7. apt-rdepends -p <package>

Synopsis: apt-rdepends --print-state <package>
Example: apt-rdepends --print-state nano

This command including --print-state option gives every output status whether it is Installed or NotInstalled. The result is exactly same with normal command, but including status. It is useful to begin learning dependency for offline installation. We choose nano as example to avoid too long output.

Reading package lists... Done
Building dependency tree       
Reading state information... Done
fping
  Depends: libc6 (>= 2.7) [Installed]
libc6
  Depends: libc-bin (= 2.15-0ubuntu10) [Installed]
  Depends: libgcc1 [Installed]
  Depends: tzdata [Installed]
libc-bin
libgcc1
  Depends: gcc-4.6-base (= 4.6.3-1ubuntu5) [Installed]
  Depends: libc6 (>= 2.2.4) [Installed]
  PreDepends: multiarch-support [Installed]
gcc-4.6-base
multiarch-support
  Depends: libc6 (>= 2.13-0ubuntu6) [Installed]
tzdata
  Depends: debconf (>= 0.5) [Installed]
  Depends: debconf-2.0 [NotInstalled]
debconf
  PreDepends: perl-base (>= 5.6.1-4) [Installed]
perl-base
  PreDepends: dpkg (>= 1.14.20) [Installed]
  PreDepends: libc6 (>= 2.11) [Installed]
dpkg
  PreDepends: coreutils (>= 5.93-1) [Installed]
  PreDepends: libbz2-1.0 [Installed]
  PreDepends: libc6 (>= 2.11) [Installed]
  PreDepends: libselinux1 (>= 1.32) [Installed]
  PreDepends: tar (>= 1.23) [Installed]
  PreDepends: xz-utils [Installed]
  PreDepends: zlib1g (>= 1:1.1.4) [Installed]
coreutils
  Depends: dpkg (>= 1.15.4) [Installed]
  Depends: install-info [Installed]
  PreDepends: libacl1 (>= 2.2.51-5) [Installed]
  PreDepends: libattr1 (>= 1:2.4.46-5) [Installed]
  PreDepends: libc6 (>= 2.15) [Installed]
  PreDepends: libselinux1 (>= 1.32) [Installed]
install-info
  Depends: libc6 (>= 2.4) [Installed]
libacl1
  Depends: libattr1 (>= 2.4.46-3) [Installed]
  Depends: libc6 (>= 2.4) [Installed]
  PreDepends: multiarch-support [Installed]
libattr1
  Depends: libc6 (>= 2.4) [Installed]
  PreDepends: multiarch-support [Installed]
libselinux1
  Depends: libc6 (>= 2.8) [Installed]
  PreDepends: multiarch-support [Installed]
libbz2-1.0
  Depends: libc6 (>= 2.4) [Installed]
  PreDepends: multiarch-support [Installed]
tar
  PreDepends: libc6 (>= 2.8) [Installed]
xz-utils
  Depends: libc6 (>= 2.7) [Installed]
  Depends: liblzma5 (>= 5.1.1alpha+20110809) [Installed]
liblzma5
  Depends: libc6 (>= 2.4) [Installed]
  PreDepends: multiarch-support [Installed]
zlib1g
  Depends: libc6 (>= 2.4) [Installed]
  PreDepends: multiarch-support [Installed]
debconf-2.0

8. apt-rdepends: Show NotInstalled Dependencies

Synopsis: apt-rdepends -p --state-show=NotInstalled --state-follow=NotInstalled <package>
Example: apt-rdepends -p --state-show=NotInstalled --state-follow=NotInstalled xchat

This command is the clearest of apt-rdepends when we want to know exactly what dependencies for a package to be downloaded for one Ubuntu system. This command is same with apt-get --print-uris below except this apt-rdepends doesn't print URL. This command firstly list the complete dependencies of package, then filter only the packages NotInstalled to show. It discards all packages has status Installed. It is basically the same when user see dependencies list every sudo apt-get install performed. So, with this command you will able to note the dependencies and go download them one by one then go back to install them completely. It will be same with apt-get install. Output from our example above will be like this.

Reading package lists... Done
Building dependency tree       
Reading state information... Done
xchat
  Depends: libsexy2 (>= 0.1.8) [NotInstalled]
  Depends: xchat-common (= 2.8.8-3ubuntu12) [NotInstalled]
libsexy2
xchat-common

9. apt-cache: Show Only Important Dependencies

10. apt-cache depends --recurse --important <package>

11. apt-cache depends --recurse --important --installed <package>

12. apt-get: List All Dependencies URL