Basic commands of dpkg

Basic commands of dpkg

Debian is one of the earliest Linux distribution around. It caught the public's fancy because of the ease of installing and uninstalling applications on it. When many other linux distributions were bogged down in dependency hell, Debian users were shielded from these problems owing to Debian's superior package handling capablities using apt-get.

All Linux distributions which claim their roots in the Debian distribution use this versatile package manager. For the uninitiated, Debian uses the deb package format for bundling together files belonging to an application. You can look at it as something like a setup installer (Eg: Installshield) in windows counterpart.

Here I will explain how to go about using this package handling utility to get the results that you desire.

The first step needed to use apt-get to your advantage is including the necessary repositories. Repositories are merely collections of softwares which are stored in a public location on the internet. By including the web address of these repositories, you are directing apt-get to search these locations for the desired software. You use the /etc/apt/sources.list file to list the addresses of the repositories. It takes the following format:

deb  [web address] [distribution name][maincontribnon-free]

For example, in Ubuntu a debian based distribution, it could be something like this:

deb http://in.archive.ubuntu.com/ubuntu breezy main restrcted

You can add any repository you like. apt-get.org contains an excellent collection of repositories to suite all tastes.

Once you have set the repositories, the next step is to sync the local software database with the database on the repositories. This will cache a copy of the list of all the remotely available softwares to your machine. This is achieved by running the following command:

# apt-get update

An advantage of this is you now have the power to search for a particular program to see if it is available for your version of distribution using the apt-cache command. And you don't need a net connection to do this. For example,

# apt-cache search baseutils

... will tell me if the package baseutils is available in the repository or not by searching the locally cached copy of the database.

Once you have figured that the package (in our case baseutils) is available, then installing it is as simple as running the following command:

# apt-get install baseutils

The real power of apt-get is realised now. If the baseutils package depends on the availability of a version of the library say, "xyz1.5.6.so". Then apt-get will download the library (or package containing the library) from the net and install it before installing baseutils package. This is known as automatic dependency resolution.

And removing a package is as simple as running the command:

# apt-get remove baseutils

Get statistics about the packages available in the repositories by running the command :

# apt-cache stats
Total package names : 22502 (900k)
Normal packages: 17632
Pure virtual packages: 281
Single virtual packages: 1048
Mixed virtual packages: 172
Missing: 3369
...

To upgrade all the softwares on your system to the latest versions, do the following:

# apt-get upgrade

And finally the king of them all - upgrading the whole distribution to a new version can be done with the command:

# apt-get dist-upgrade

Saving valuable hard disk space

Each time you install an application using apt-get, the package is actually cached in a location on your hard disk. It is usually stored in the location /var/cache/apt/archives/ . Over a period of time, all the cached packages will eat up your valuable hard disk space. You can clear the cache and release hard disk space by using the following command:

# apt-get clean

You could also use autoclean where in, only those packages in the cache which are found useless or partially complete are deleted.

# apt-get autoclean

dpkg - The low level Package management utility

As I said earlier, Debian based distributions use the Deb package format. Usually normal users like you and me are shielded from handling individual deb packages. But if you fall into a situation where you have to install a deb package you use the dpkg utility.

Lets assume I have a deb package called gedit-2.12.1.deb and I want to install it on my machine. I do it using the following command:

# dpkg -i gedit-2.12.1.deb

To remove an installed package, run the command:

# dpkg -r gedit

The main thing to note above is I have used only the name of the program and not the version number while removing the software.

You may also use the --purge (-P) flag for removing software.

# dpkg -P gedit

This will remove gedit along with all its configuration files. Where as -r (--remove) does not delete the configuration files.

Now lets say I do not want to actually install a package but want to see the contents of a Deb package. This can be achieved using the -c flag:

# dpkg -c gedit-2.12.1.deb

To get more information about a package like the authors name,the year in which it was compiled and a short description of its use, you use the -I flag:

# dpkg -I gedit-2.12.1.deb

You can even use wild cards to list the packages on your machine. For example, to see all the gcc packages on your machine, do the following:

# dpkg -l gcc*

Desired=Unknown/Install/Remove/Purge/Hold
Status=Not/Installed/Config-files/Unpacked/Failed-config/.
/ Err?=(none)/Hold/Reinst-required/X=both-problems
/ Name            Version        Description
+++-===============-==============-========================
ii  gcc             4.0.1-3        The GNU C compiler
ii  gcc-3.3-base    3.3.6-8ubuntu1 The GNU Compiler Colletio
un  gcc-3.5         none          (no description available)
un  gcc-3.5-base    none          (no description available)
un  gcc-3.5-doc     none          (no description available)
ii  gcc-4.0         4.0.1-4ubuntu9 The GNU C compiler
...

In the above listing, the first 'i' denotes desired state which is install. The second 'i' denotes the actual state ie gcc is installed. The third column gives the error problems if any. The fourth, fifth and sixth column gives the name, version and description of the packages respectively. And gcc-3.5 is not installed on my machine. So the status is given as 'un' which is unknown not-installed.

To check if an individual package is installed, you use the status -s flag:

# dpkg -s gedit

Two days back, I installed beagle (a real time search tool based on Mono) on my machine. But I didn't have a clue about the location of the files as well as what files were installed along with beagle. That was when I used the -L option to get a list of all the files installed by the beagle package.

# dpkg -L beagle

Even better, you can combine the above command with grep to get a listing of all the html documentation of beagle.

# dpkg -L beagle | grep html$

These are just a small sample of the options you can use with dpkg utility. To know more about this tool, check its man page.

If you are alergic to excessive command line activities, then you may also use dselect which is a curses based menu driven front-end to the low level dpkg utility.

dpkg -S | --search filename-search-pattern ...
Search for a filename from installed packages. All standard shell wildchars can be used in the pattern.


dpkg -p|--print-avail package
Display details about package, as found in /var/lib/dpkg/available.


dpkg --update-avail | --merge-avail Packages-file
Update dpkg's and dselect's idea of which packages are available. With action --merge-avail, old information is combined with information from Packages-file. With action --update-avail, old information is replaced with the information in the Packages-file. The Packages-file distributed with Debian GNU/Linux is simply named Packages. dpkg keeps its record of available packages in /var/lib/dpkg/available.


dpkg -A | --record-avail package_file ...
Update dpkg and dselect's idea of which packages are available with information from the package package_file. If --recursive or -R option is specified, package_file must refer to a directory instead.


dpkg -l | --list package-name-pattern ...
List packages matching given pattern. If no package-name-pattern is given, list all packages in /var/lib/dpkg/available. Normal shell wildchars are allowed in package-name-pattern. (You will probably have to quote package-name-pattern to prevent the shell from performing filename expansion. For example, dpkg -l 'libc5*' will list all the package names starting with "libc5".)


dpkg -s | --status package-name ...
Report status of specified package. This just displays the entry in the installed package status database.


Get a list of everything you've installed?
dpkg -l '*'


List each available package whose name matches thunderbird.
# apt-cache pkgnames | grep thunderbird


"dpkg --force-help" is your friend.

What is a shell in Unix

The shell acts as an interface between the user and the kernel. When a user logs in, the login program checks the username and password, and then starts another program called the shell. The shell is a command line interpreter (CLI). It interprets the commands the user types in and arranges for them to be carried out. The commands are themselves programs: when they terminate, the shell gives the user another prompt (% on our systems).

The adept user can customise his/her own shell, and users can use different shells on the same machine. Staff and students in the school have the tcsh shell by default.

The tcsh shell has certain features to help the user inputting commands.

Filename Completion - By typing part of the name of a command, filename or directory and pressing the [Tab] key, the tcsh shell will complete the rest of the name automatically. If the shell finds more than one name beginning with those letters you have typed, it will beep, prompting you to type a few more letters before pressing the tab key again.

History - The shell keeps a list of the commands you have typed in. If you need to repeat a command, use the cursor keys to scroll up and down the list or type history for a list of previous commands.