Important Update
Apparently the new version of apt-get in Edgy Eft (Ubuntu 6.10) has a function that allows you to remove unused dependencies when removing an application:
sudo apt-get autoremove applicationname
So the points outlined on this page about using aptitude over apt-get are largely irrelevant if you're using Edgy Eft (6.10), Feisty Fawn (7.04), or any future version of Ubuntu.
Information Relevant to Older Versions of Ubuntu
You may notice that many Ubuntu websites ask you to install software using the apt-get command. Others may use the aptitude command instead. In many ways, they're the same in that they both draw from the repositories in your /etc/apt/sources.list to retrieve and install software.
Below is the demonstrated difference, though, at least for Ubuntu 6.06 and earlier. The example displayed is the package kword, but it works the same for any package that has dependencies.
Both aptitude and apt-get will install kword and its dependencies (kspread, kword-data, and libwv2-1c2), but only aptitude will actually remove the dependencies when kword is removed (and only if no other packages depend on those dependencies).
Note: In order for aptitude to work properly, you must first do an update, then an install. Also, you cannot install with apt-get or Synaptic and then expect to have dependencies removed by uninstalling with aptitude.
If you were unfortunate enough to use apt-get, and you want to clean out some unused dependencies, you can install and use deborphan or the graphical frontend gtkorphan (now available in Dapper if you enable extra repositories). Naturally, you would install it this way:
sudo aptitude update
sudo aptitude install gtkorphan
On to the demonstrations...
Aptitude Demonstration:
username@ubuntu:~$ sudo aptitude update && sudo aptitude install kword
Password:
Reading package lists... Done
Building dependency tree... Done
Reading extended state information
Initializing package states... Done
Building tag database... Done
Get:1 http://security.ubuntu.com dapper-security Release.gpg [189B]
Get:2 http://archive.ubuntu.com dapper Release.gpg [189B]
Get:3 http://archive.ubuntu.com dapper-updates Release.gpg [189B]
Get:4 http://security.ubuntu.com dapper-security Release [27.0kB]
Get:5 http://archive.ubuntu.com dapper-backports Release.gpg [189B]
Hit http://archive.ubuntu.com dapper Release
Get:6 http://archive.ubuntu.com dapper-updates Release [27.0kB]
Ign http://packages.freecontrib.org dapper Release.gpg
Ign http://packages.freecontrib.org dapper Release
Get:7 http://archive.ubuntu.com dapper-backports Release [19.6kB]
Ign http://packages.freecontrib.org dapper/free Packages
Get:8 http://security.ubuntu.com dapper-security/main Packages [14.4kB]
Hit http://archive.ubuntu.com dapper/main Packages
Get:9 http://archive.ubuntu.com dapper/restricted Packages [4571B]
Hit http://archive.ubuntu.com dapper/main Sources
Get:10 http://archive.ubuntu.com dapper/restricted Sources [1478B]
Hit http://archive.ubuntu.com dapper/universe Packages
Hit http://archive.ubuntu.com dapper/universe Sources
Get:11 http://archive.ubuntu.com dapper/multiverse Packages [95.2kB]
Ign http://packages.freecontrib.org dapper/non-free Packages
Get:12 http://security.ubuntu.com dapper-security/restricted Packages [14B]
Get:13 http://security.ubuntu.com dapper-security/main Sources [3593B]
Get:14 http://security.ubuntu.com dapper-security/restricted Sources [14B]
Get:15 http://security.ubuntu.com dapper-security/universe Packages [3762B]
Get:16 http://security.ubuntu.com dapper-security/universe Sources [14B]
Ign http://packages.freecontrib.org dapper/free Sources
Ign http://packages.freecontrib.org dapper/non-free Sources
Get:17 http://archive.ubuntu.com dapper/multiverse Sources [46.6kB]
Hit http://packages.freecontrib.org dapper/free Packages
Get:18 http://archive.ubuntu.com dapper-updates/main Packages [10.2kB]
Get:19 http://archive.ubuntu.com dapper-updates/restricted Packages [14B]
Get:20 http://archive.ubuntu.com dapper-updates/main Sources [9006B]
Get:21 http://archive.ubuntu.com dapper-updates/restricted Sources [14B]
Get:22 http://archive.ubuntu.com dapper-backports/main Packages [14B]
Get:23 http://archive.ubuntu.com dapper-backports/restricted Packages [14B]
Get:24 http://archive.ubuntu.com dapper-backports/universe Packages [14B]
Get:25 http://archive.ubuntu.com dapper-backports/multiverse Packages [14B]
Hit http://packages.freecontrib.org dapper/non-free Packages
Hit http://packages.freecontrib.org dapper/free Sources
Hit http://packages.freecontrib.org dapper/non-free Sources
Fetched 263kB in 2s (89.0kB/s)
Reading package lists... Done
Reading package lists... Done
Building dependency tree... Done
Reading extended state information
Initializing package states... Done
Building tag database... Done
The following NEW packages will be automatically installed:
kspread kword-data libwv2-1c2
The following NEW packages will be installed:
kspread kword kword-data libwv2-1c2
0 packages upgraded, 4 newly installed, 0 to remove and 0 not upgraded.
Need to get 6613kB of archives. After unpacking 18.9MB will be used.
Do you want to continue? [Y/n/?] y
Writing extended state information... Done
Get:1 http://archive.ubuntu.com dapper/main kspread 1:1.5.0-0ubuntu9 [2276kB]
Get:2 http://archive.ubuntu.com dapper/main libwv2-1c2 0.2.2-5 [225kB]
Get:3 http://archive.ubuntu.com dapper/main kword-data 1:1.5.0-0ubuntu9 [1590kB]
Get:4 http://archive.ubuntu.com dapper/main kword 1:1.5.0-0ubuntu9 [2522kB]
Fetched 6613kB in 45s (146kB/s)
Selecting previously deselected package kspread.
(Reading database ... 110852 files and directories currently installed.)
Unpacking kspread (from .../kspread_1%3a1.5.0-0ubuntu9_i386.deb) ...
Selecting previously deselected package libwv2-1c2.
Unpacking libwv2-1c2 (from .../libwv2-1c2_0.2.2-5_i386.deb) ...
Selecting previously deselected package kword-data.
Unpacking kword-data (from .../kword-data_1%3a1.5.0-0ubuntu9_all.deb) ...
Selecting previously deselected package kword.
Unpacking kword (from .../kword_1%3a1.5.0-0ubuntu9_i386.deb) ...
Setting up kspread (1.5.0-0ubuntu9) ...
Setting up libwv2-1c2 (0.2.2-5) ...
Setting up kword-data (1.5.0-0ubuntu9) ...
Setting up kword (1.5.0-0ubuntu9) ...
username@ubuntu:~$ sudo aptitude remove kword
Reading package lists... Done
Building dependency tree... Done
Reading extended state information
Initializing package states... Done
Building tag database... Done
The following packages are unused and will be REMOVED:
kspread kword-data libwv2-1c2
The following packages will be REMOVED:
kword
0 packages upgraded, 0 newly installed, 4 to remove and 0 not upgraded.
Need to get 0B of archives. After unpacking 18.9MB will be freed.
Do you want to continue? [Y/n/?] y
Writing extended state information... Done
(Reading database ... 111678 files and directories currently installed.)
Removing kword ...
Removing kspread ...
Removing kword-data ...
Removing libwv2-1c2 ...
username@ubuntu:~$
Apt-get Demonstration:
username@ubuntu:~$ sudo apt-get update && sudo apt-get install kword
Get:1 http://security.ubuntu.com dapper-security Release.gpg [189B]
Get:2 http://archive.ubuntu.com dapper Release.gpg [189B]
Get:3 http://archive.ubuntu.com dapper-updates Release.gpg [189B]
Get:4 http://archive.ubuntu.com dapper-backports Release.gpg [189B]
Hit http://security.ubuntu.com dapper-security Release
Hit http://archive.ubuntu.com dapper Release
Hit http://archive.ubuntu.com dapper-updates Release
Hit http://security.ubuntu.com dapper-security/main Packages
Hit http://archive.ubuntu.com dapper-backports Release
Hit http://archive.ubuntu.com dapper/main Packages
Hit http://archive.ubuntu.com dapper/restricted Packages
Hit http://archive.ubuntu.com dapper/main Sources
Ign http://packages.freecontrib.org dapper Release.gpg
Hit http://security.ubuntu.com dapper-security/restricted Packages
Hit http://security.ubuntu.com dapper-security/main Sources
Hit http://security.ubuntu.com dapper-security/restricted Sources
Hit http://archive.ubuntu.com dapper/restricted Sources
Hit http://archive.ubuntu.com dapper/universe Packages
Hit http://archive.ubuntu.com dapper/universe Sources
Hit http://archive.ubuntu.com dapper/multiverse Packages
Hit http://archive.ubuntu.com dapper/multiverse Sources
Ign http://packages.freecontrib.org dapper Release
Hit http://archive.ubuntu.com dapper-updates/main Packages
Hit http://archive.ubuntu.com dapper-updates/restricted Packages
Hit http://archive.ubuntu.com dapper-updates/main Sources
Hit http://archive.ubuntu.com dapper-updates/restricted Sources
Hit http://security.ubuntu.com dapper-security/universe Packages
Hit http://security.ubuntu.com dapper-security/universe Sources
Ign http://packages.freecontrib.org dapper/free Packages
Ign http://packages.freecontrib.org dapper/non-free Packages
Ign http://packages.freecontrib.org dapper/free Sources
Ign http://packages.freecontrib.org dapper/non-free Sources
Hit http://packages.freecontrib.org dapper/free Packages
Hit http://archive.ubuntu.com dapper-backports/main Packages
Hit http://packages.freecontrib.org dapper/non-free Packages
Hit http://packages.freecontrib.org dapper/free Sources
Hit http://archive.ubuntu.com dapper-backports/restricted Packages
Hit http://archive.ubuntu.com dapper-backports/universe Packages
Hit http://archive.ubuntu.com dapper-backports/multiverse Packages
Hit http://packages.freecontrib.org dapper/non-free Sources
Fetched 4B in 2s (2B/s)
Reading package lists... Done
Reading package lists... Done
Building dependency tree... Done
The following extra packages will be installed:
kspread kword-data libwv2-1c2
Suggested packages:
koffice-doc-html
The following NEW packages will be installed:
kspread kword kword-data libwv2-1c2
0 upgraded, 4 newly installed, 0 to remove and 0 not upgraded.
Need to get 0B/6613kB of archives.
After unpacking 18.9MB of additional disk space will be used.
Do you want to continue [Y/n]? y
Selecting previously deselected package kspread.
(Reading database ... 110852 files and directories currently installed.)
Unpacking kspread (from .../kspread_1%3a1.5.0-0ubuntu9_i386.deb) ...
Selecting previously deselected package libwv2-1c2.
Unpacking libwv2-1c2 (from .../libwv2-1c2_0.2.2-5_i386.deb) ...
Selecting previously deselected package kword-data.
Unpacking kword-data (from .../kword-data_1%3a1.5.0-0ubuntu9_all.deb) ...
Selecting previously deselected package kword.
Unpacking kword (from .../kword_1%3a1.5.0-0ubuntu9_i386.deb) ...
Setting up kspread (1.5.0-0ubuntu9) ...
Setting up libwv2-1c2 (0.2.2-5) ...
Setting up kword-data (1.5.0-0ubuntu9) ...
Setting up kword (1.5.0-0ubuntu9) ...
username@ubuntu:~$ sudo apt-get remove kword
Reading package lists... Done
Building dependency tree... Done
The following packages will be REMOVED:
kword
0 upgraded, 0 newly installed, 1 to remove and 0 not upgraded.
Need to get 0B of archives.
After unpacking 7000kB disk space will be freed.
Do you want to continue [Y/n]? y
(Reading database ... 111678 files and directories currently installed.)
Removing kword ...
username@ubuntu:~$