Finding and Installing Packages

Transcription

1 Finding and Installing Packages Your course leader is Susan Hutchinson. Susan is a support specialist for Linux and Windows in the Department of Statistics. Her address is hutchins@stats.ox.ac.uk. These courses were developed jointly with Dr Jon Lockley, who is Computing Manager at the Oxford Super Computer centre.

2 Today's session We start by exploring techniques for finding and evaluating software packages new applications for Linux. We will look at how packages are downloaded and how new packages are installed. We will also look briefly at system administration. Exercises We will explore different approaches for evaluating applications. Then we will download and install one of these applications. Three different approaches to package installation will be attempted in the exercises: one very easy, one fairly easy and one difficult. We will also look at the privileged account root which is there to enable us to make changes to the system.

3 How to get advice What do you do if you need to install some new software? How do you make a choice? Newsgroups Magazines Books Google Websites What happens if you need to do something that your Linux system has not been set up to do? For example this Ubuntu CD does not contain an application for creating and editing web pages. How do you go about finding out what your options are and which is the best one for you and for your distribution? Alternatively as a new Linux user how do you decide which reader will suit you best? Linux Format is a friendly magazine which often has free CDs with Linux software or complete distributions. There are also often tutorials and introductions for beginners (or newbies). The website is an excellent place to start. Other websites such as and are very useful indeed.

4 Evaluating the information Ask good questions. Look in different places. Experience what has worked in the past? Websites up-to-date; well maintained? Understand how search engines work. All pages on the web are visited and the links they make to other pages are stored; Each page is assigned a ranking depending on how many other pages link to it; Results are listed in order of links to that page. An example of a bad question to ask is Which is the best reader?. This is likely to start a flame war where surprisingly ferocious opinions are expressed. A good question would be What is a good reader for a beginner? together with details of your setup. It can also be helpful to include the Linux distro you are using. This is particularly important if you you are going to post a technical question. I cannot get sound working is not a good question; I cannot get sound working on my Fedora 8 PC with all the latest updates and the make of sound card. Evaluating the content of websites comes with experience but some pointers help. Is the information up-to-date? How well maintained is the site? Did the information appear anywhere else? How easy was it to find?

5 Managing software Different Linux distributions manage software packages in different ways. There are two main approaches: RPM Redhat Package Manager is used by Redhat, Mandriva and Suse. APT Advanced Package Tool - is used by Debian, Ubuntu and Knoppix. As you may now expect there are different ways to manage software installation on different Linux distributions. Both are used from the command line, but APT has a graphical version available. Newer versions of some Redhat distributions also have a GUI version.

6 Why manage packages? Complexity of current systems. Dependencies existing applications may affect new software. Each system may be configured slightly differently to suit its own environment. Enormous range of hardware that must be supported. We don't want if possible to concern ourselves with these details when we need to install some new packages. Additionally, as with Windows a mechanism is needed to keep the system up-to-date. Why do we need package managers.? We have already seen the enormous range of software available in Linux. Developers cannot predict always what other packages will be used on the same system as their software; how the system is set up or what version or distribution is being used. Some method of managing these problems was needed. Both package managers keep a database of information about software installed on the system which is used as a reference when a new package is installed. A means of keeping a system up-to-date is also needed. You could view these package managers as similar to Windows Install Shield.

7 Redhat Package Manager Each package comes bundled as a single file called an RPM. A bundle may include program files, libraries, help files and configuration files. There is also an rpm command which allows you to install, query and remove packages. RPM keeps a database of packages that have been installed and the files that relate to that package. RPM which is the name of the manager, the command used to manage packages and the type of file containing a new package is widely used. There are limitations. In particular it is sometimes hard to make sure that you download the correct version of the software that is suitable for your system. RPM will however check dependencies and report what other packages are needed before your software can be installed.

8 RPM continued Need to find each software package and download it. Locations where huge numbers of packages are stored are called repositories. Can be used with Yum Yellowdog Updater, Modified to download packages from a repository. Provides a way of keeping your system up-to-date. Yum provides a useful addition to RPM. It allows you to set up automatic updates. Keeping a system up-to-date is important to ensure that security vulnerabilities are addressed. Other distributions such as SUSE use a similar package called YaST.

9 Advanced Package Tool Provides both local installation and repository downloads in one set of commands. Not dependent on one package format. Very powerful tool that appears straightforward to use. Graphical frontend kpackage is also available APT is a rather more flexible and powerful version of RPM and yum. It can also deal with software in different formats. I have little experience of setting up an APT system from scratch but this version of Ubuntu comes configured to run apt successfully.

10 Other ways of installing software The hard way: Software is not always bundled in a format that APT or RPM can use. It will come in a single.tgz or.tar.gz or.bz2 file. Also known as a tarball. Requires rather more knowledge of the system. Until now we have looked at software that has been easy to download and install. We have not had to concern ourselves with the details of what version we need or where to go to download the software. But there will be times when this is not possible so that we will have to find the software ourselves. It will then need configuring, building and installing by hand. One of the many disadvantages with this system is that it is then much harder to remove the software afterwards as it is not always obvious whereabouts on the system all the files have been copied.

11 Managing your system Until now we have used the the system to change our files but not made any system changes. Unlike Windows, Linux has a clear and rigid distinction between using a system and making changes to a system, such as installing new software. So to make changes a special account is needed. This separation of powers is fundamental to the way Linux (and Unix) systems are designed. As you may remember from an earlier session you were able to move around the whole system but could not remove files apart from those in your home directory.

12 The root account In most Linux systems you will have your own username and password. Standard user accounts are set up so that you can change your own home files but not any system files. To install new software we need an account that can change files anywhere on the system. This account is known as the root account. Note that because Ubuntu is running from CD separate user accounts are not configured. To run commands as root you need to use sudo command in a command tool Window and press enter. You should now see a different prompt: a #. This a standard Unix/Linux convention for indicating that this account is privileged and so dangerous.

13 The root account continued Because this is a powerful account you are advised to use it only when necessary. Careless use can entirely wreck your system. Use a different desktop if possible Better to become root from your own account rather than log on as root. It is good practice to use the root account only in a command tool window rather than logging on as root directly. In this way you are less likely to damage the system. Consider the effect of typing cd /usr/bin rm * or even worse rm -rf * as root.. You can try this at the end of your practical!

14 Exercises We will investigate various HTML editors and then install one of them in three different ways: Using Add/Remove Applications... Using apt-get from the command line. Downloading and installing a tarball.