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For a specific package, can I find out why it is installed?

So, can I see or it's manually installed, or that it is installed as a dependency of another package? Or that it is installed as part of the distro?

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This is related to (a part of) this question, see this answer for details. –  koushik Oct 10 '10 at 14:34
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4 Answers

up vote 22 down vote accepted

A quick solution is:

aptitude why $package

With the following command

apt-cache rdepends $package

you can see what are the other packages that depend directly on this package, and this can help in understand. You can add the --recurse option, to list all packages that depends directly or indirectly on this package.

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Pity aptitude isn't included by default :( –  badp Oct 10 '10 at 14:21
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@badp thank you to point out. This is the bad new with maverick, only to save some space on the livecd iso image. But it is an invaluable tool, and i will not go without. –  enzotib Oct 10 '10 at 14:31
    
apt-cache rdepends --recurse $package probably gives too many packages. I would add --installed option to restrict to installed packages. -i option restricts to pre-dependence and dependence related packages. But a package may be installed because it is recommended by another package. To include such recommendation relateded packages, I suppose this would give the right ones: apt-cache rdepends --no-suggests --no-conflicts --no-breaks --no-replaces --no-enhances --installed --recurse $package –  jarno Dec 22 '13 at 18:20
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Yes, you can, and it's a pretty obvious command, in fact. Assuming you've aptitude installed, you can open up a Terminal Window ad type:

aptitude why package

That should give a list of packages that depend on that specific package. If it's a manually installed package, it will say something like "It wasn't possible to find a reason to install package".

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You can also use plain dpkg .

For example, dpkg -p [PACKAGE NAME] provides its information:

Example : if [ PACKAGE NAME ] is zip

dpkg -p zip  
Package: zip  
Priority: optional  
Section: utils  
Installed-Size: 616  
Maintainer: Ubuntu Developers <ubuntu-devel-discuss@lists.ubuntu.com>  
Architecture: i386  
Version: 3.0-2  
Replaces: zip-crypt (<= 2.30-2)  
Depends: libbz2-1.0, libc6 (>= 2.7)  
Recommends: unzip  
Conflicts: zip-crypt (<= 2.30-2)  
Size: 318238  
Description: Archiver for .zip files  
 This is InfoZIP's zip program. It produces files that are fully  
 compatible with the popular PKZIP program; however, the command line  
 options are not identical. In other words, the end result is the same,  
 but the methods differ. :-)  
 .  
 This version supports encryption.  
Original-Maintainer: Santiago Vila <sanvila@debian.org>  
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Here's a simple way that doesn't rely on aptitude, which 10.10 doesn't ship by default anymore.

Notice

You do need root access to run these commands.

Graphically

Open Synaptic and try to remove it.

If a dialog pops up asking you to delete other packages, those are the packages that (recursively) depend upon it.

From terminal

apt-get remove package_name_goes_here -s

Again, the packages that would be removed as a result are all those that (recursively) depend on it. (The -s parameter tells apt-get to not actually remove the package.)

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This is a risky solution because it could actually remove the package and all dependencies if they mis-click. –  ImaginaryRobots Oct 10 '10 at 15:41
    
@ImaginaryRobots, that's a lot of misclicking. (You have to misclick Ok on the first dialog, then Apply, then again Ok on the confirmation dialog.) For the terminal version, there's also an extra y/N confirmation request should you typo -s. I added a warning however. –  badp Oct 10 '10 at 15:44
    
-1 as this information is availble in Synaptic under the dependencies tab, when viewing the properties of a package. –  alexanderpas Oct 29 '10 at 22:46
    
@alex incorrect - that dialog doesn't tell you whether that package is installed manually or automatically. PS: Inbox counter reset, try harder. –  badp Oct 29 '10 at 22:52
    
@badp no, but that info can be found with the "Installed (manual)" status filter on the main screen, and can be seen in the package menu when you select a package. –  alexanderpas Oct 29 '10 at 23:42
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