Chapter 9. Managing Software
The following topics are covered in this chapter:
The following RHCSA exam objectives are covered in this chapter:
Install and update software packages from Red Hat Network, a remote repository, or from the local file system
Work with package module streams
Managing software packages is an important task for an administrator of Red Hat Enterprise Linux. In this chapter, you learn how to manage software packages from the command line by using the yum utility. You also learn which role repositories play in software management with YUM. Next we’ll cover working with Package Module Streams, a solution that makes it possible to work with the specific version packages that you need in your environment. In the last part of this chapter, you learn how to manage software with the rpm command, which is useful to query new and installed software packages.
“Do I Know This Already?” Quiz
The “Do I Know This Already?” quiz allows you to assess whether you should read this entire chapter thoroughly or jump to the “Exam Preparation Tasks” section. If you are in doubt about your answers to these questions or your own assessment of your knowledge of the topics, read the entire chapter. Table 9-1 lists the major headings in this chapter and their corresponding “Do I Know This Already?” quiz questions. You can find the answers in Appendix A, “Answers to the ‘Do I Know This Already?’ Quizzes and ‘Review Questions.’”
Table 9-1 “Do I Know This Already?” Section-to-Question Mapping
Foundation Topics Section |
Questions |
|---|---|
1–4 |
|
5 |
|
6–7 |
|
8–10 |
1. Which of the following is not a mandatory component in a .repo file that is used to indicate which repositories should be used?
a. [label]
b. name=
c. baseurl=
d. gpgcheck=
2. Which installation source is used on RHEL if a server is not registered with RHN?
a. The installation medium is used.
b. No installation source is used.
c. The base RHN repository is used, without updates.
d. You have full access to RHN repositories, but the software you are using is not supported.
3. Which of the following should be used in the .repo file to refer to a repository that is in the directory /repo on the local file system?
a. file=/repo
b. baseurl=file://repo
c. baseurl=file:///repo
d. file=http:///repo
4. Which of the following is true about GPG-based repository security?
a. If packages in the repository have been signed, you need to copy the GPG key to the correct location.
b. GPG package signing is mandatory.
c. GPG package signatures prevent packages in a repository from being changed.
d. GPG package signing is recommended on Internet repositories, but not required on local repositories that are for internal use only.
5. Which command enables you to search the package that contains the file semanage?
a. yum search semanage
b. yum search all semanage
c. yum provides semanage
d. yum whatprovides */semanage
6. Which YUM module component allows you to work with different versions side by side?
b. Application stream
c. Module version
d. RPM group
7. Which of the following commands allows you to install the devel profile of the PHP 7.1 application stream?
a. yum module install php:7.1 devel
b. yum module install php:7.1 --devel
c. yum module install php:7.1/devel
d. yum module install php:7.1@devel
8. Which command should you use to install an RPM file that has been downloaded to your computer?
a. yum install
b. yum localinstall
c. rpm -ivh
d. rpm -Uvh
9. Which command enables you to find the RPM package a specific file belongs to?
a. rpm -ql /my/file
b. rpm -qlf /my/file
c. rpm -qf /my/file
d. rom -qa /my/file
10. Which command enables you to analyze whether there are scripts in an RPM package file that you have just downloaded?
a. rpm -qs packagename.rpm
b. rpm -qps packagename.rpm
c. rpm -qp --scripts packagename.rpm
d. rpm -q --scripts packagename.rpm
Foundation Topics
Managing Software Packages with yum
The default utility used to manage software packages on Red Hat Enterprise Linux is yum, which stands for Yellowdog Updater, Modified. Yum is designed to work with repositories, which are online depots of available software packages. In this section, you learn how to create and manage repositories and how to manage software packages based on the contents of the repositories.
Note
Software in RHEL is based on Fedora Software. In the versions of Fedora that RHEL 8 is based on, yum recently has been replaced with the dnf utility. For that reason, it was expected that with the release of RHEL 8, the yum command would be replaced with the dnf command. Red Hat has decided differently. With RHEL 8, a new version of yum has been introduced, which is based on the dnf command. You’ll notice that in many cases, when requesting information about yum, you’re redirected to dnf resources. So in fact you’re using dnf, but Red Hat has decided to rename it to yum. Even if in reality you’re using the dnf command, in this book I’m following the Red Hat convention, and for that reason you’ll learn how to work with yum.
Understanding the Role of Repositories
Software on Red Hat Enterprise Linux is provided in the RPM (Red Hat Package Manager) format. This is a specific format used to archive the package and provide package metadata as well.
When you are working with software in RHEL, repositories play a key role. Working with repositories makes it easy to keep your server current: The maintainer of the repository publishes updated packages in the repository, and the result is that whenever you use the yum command (discussed later in this chapter) to install software, the most recent version of the software is automatically used.
Another major benefit of working with YUM is the way that package dependencies are dealt with. On Linux (as on most other modern operating systems), software packages have dependencies. This means that to install one package, other packages have to be present as well. Without using repositories, that would mean that these packages have to be installed manually.
The YUM repository system takes care of resolving these dependencies automatically. If a package is going to be installed, it contains information about the required dependencies. The yum command then looks in the repositories configured on this system to fetch the dependencies automatically. If all goes well, the installer just sees a short list of the dependencies that will be installed as a dependency to install the package. If you are using RHEL with the repositories that are provided through Red Hat Network (RHN), there is no reason why this procedure should not work, and the attempts to install software will usually succeed.
While installing RHEL 8, it asks you to register with the Red Hat Customer Portal, which provides different repositories. After registering, you can install software packages that are verified by Red Hat automatically. If you choose to install RHEL without registration, it cannot get in touch with the Red Hat repositories, and you end up with no repositories at all. In that case, you have to be able to specify yourself which repository you want to use. If you are using CentOS, you get access to the CentOS repositories and no registration is required.
Note that repositories are specific to an operating system. Therefore, if you are using RHEL, you should use RHEL repositories only. Do not try, for instance, to add CentOS repositories to a RHEL server. If you want to provide additional software from the Fedora project to a RHEL server (which for support reasons is not recommended), you can consider adding the EPEL (Extra Packages for Enterprise Linux) repositories. See https://fedoraproject.org/wiki/EPEL for more information.
Warning
Before adding the EPEL repository to RHEL, make sure that it doesn’t break your current support status. EPEL packages are not managed by Red Hat, and adding them make break supported Red Hat packages.
Registering Red Hat Enterprise Linux for Support
Red Hat Enterprise Linux is a supported Linux operating system that requires you to register. To register RHEL, you need a valid entitlement. This entitlement is associated to your account on the Red Had Customer Portal. You can obtain an entitlement by purchasing a subscription for RHEL or by joining the Red Hat Developer program, which gives access to the no-cost Red Hat Enterprise Developer subscription. You can sign up for the Red Hat Developer subscription at https://developers.redhat.com.
After obtaining a valid subscription for Red Hat Enterprise Linux, you can use the Red Hat Subscription Management (RHSM) tools to manage your entitlement. Managing an entitlement involves four basic tasks:
Register: While registering a subscription, you connect it to your current Red Hat account. As a result, the subscription-manager tool can inventory the system. If a system is no longer used, it can also be unregistered.
Subscribe: Subscribing a system gives it access to updates for Red Hat products that your subscription is entitled to. Also, by subscribing, you’ll get access to the support level that is associated with your account.
Enable repositories: After subscribing a system, you’ll get access to a default set of repositories. Some repositories by default are disabled but can be enabled after subscribing your system.
Review and track: You can review and track current subscriptions that are in use.
Managing Subscriptions
You can manage subscriptions either from the GNOME graphical interface or from the command line. The subscription-manager tool is used for managing subscriptions from the command line. You can use it in the following ways:
Register a system: Type subscription-manager register to register. It will prompt for the name of your Red Hat user account as well as your password, and after entering these, your RHEL server will be registered.
List available subscriptions: Each account has access to specific subscriptions. Type subscription-manager list --available to see what your account is entitled to.
Automatically attach a subscription: Registering a server is not enough to get access to the repositories. Use subscription-manager attach --auto to automatically attach your subscription to the repositories that are available.
Get an overview: To see which subscriptions you’re currently using, type subscription-manager --consumed.
Unregister: If you’re going to deprovision a system, use subscription-manager unregister. If you have access to a limited number of registered systems only, unregistering is important to ensure that you don’t run out of available licenses.
After registering and attaching a subscription, entitlement certificates are written to the /etc/pki directory. In /etc/pki/product, certificates are stored that indicate which Red Hat products are installed on this system. In /etc/pki/consumer, certificates are stored that identify the Red Hat account to which the system is registered, and the /etc/pki/entitlement directory contains information about the subscriptions that are attached to this system.
Specifying Which Repository to Use
On most occasions, after the installation of your server has finished, it is configured with a list of repositories that should be used. You sometimes have to tell your server which repositories should be used:
You want to distribute nondefault software packages through repositories.
You are installing Red Hat Enterprise Linux without registering it on RHN.
Telling your server which repository to use is not difficult, but it is important that you know how to do it (for the RHCSA exam, too).
Important!
To learn how to work with repositories and software packages, do not use the repositories that are provided by default. So if you have installed RHEL, do not register using subscription-manager, and if you have installed CentOS, remove all files from /etc/yum.repos.d.
To tell your server which repository to use, you need to create a file with a name that ends in .repo in the directory /etc/yum.repos.d. In that file you need the following contents:
[label] The .repo file can contain different repositories, each section starting with a label that identifies the specific repository.
name= Use this to specify the name of the repository you want to use.
baseurl= Contains the URL that points to the specific repository location.
In the repository files that are provided by default, you may find several repositories in one file, as is the case in Example 9-1. This is useful to group repositories that belong together in one file, and is often done in repository files that are provided as a default. If you are creating repository files yourself, you are free to create separate files for each repository.
Example 9-1 shows a repository file that is based on the default repositories that are installed on CentOS 8.
Example 9-1 Repository File Example
[root@server1 yum.repos.d]# cat CentOS-Base.repo # CentOS-Base.repo # # The mirror system uses the connecting IP address of the client and the # update status of each mirror to pick mirrors that are updated to and # geographically close to the client. You should use this for CentOS updates # unless you are manually picking other mirrors. # # If the mirrorlist= does not work for you, as a fall back you can try the # remarked out baseurl= line instead. # # [base] name=CentOS-$releasever - Base mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch= $basearch&repo=os #baseurl=http://mirror.centos.org/centos/$releasever/os/$basearch/ gpgcheck=1 gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-8 #released updates [updates] name=CentOS-$releasever - Updates mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch= $basearch&repo=updates #baseurl=http://mirror.centos.org/centos/$releasever/updates/$basearch/ gpgcheck=1 gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-8 #additional packages that may be useful [extras] name=CentOS-$releasever - Extras mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch= $basearch&repo=extras #baseurl=http://mirror.centos.org/centos/$releasever/extras/$basearch/ gpgcheck=1 gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-8 #additional packages that extend functionality of existing packages [centosplus] name=CentOS-$releasever - Plus mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch= $basearch&repo=centosplus #baseurl=http://mirror.centos.org/centos/$releasever/centosplus/ $basearch/ gpgcheck=1 enabled=0 gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-8
In the repository configuration file from Example 9-1, you can see that some options are used. Table 9-2 summarizes these options.
Table 9-2 Key Options in .repo Files
Option |
Explanation |
|---|---|
[label] |
The label used as an identifier in the repository file. |
name= |
Specifies the name of the repository. |
mirrorlist= |
Refers to a URL where information about mirror servers for this server can be obtained. Typically used for big online repositories only. |
baseurl= |
Refers to the base URL where the RPM packages are found. |
gpgcheck= |
Set to 1 if a GNU Privacy Guard (GPG) integrity check needs to be performed on the packages. If set to 1, a GPG key is required. |
gpgkey= |
Specifies the location of the GPG key that is used to check package integrity. |
When creating a repository file, the baseurl parameter is the most important because it tells your server where to find the files that are to be installed. The baseurl takes as its argument the URL where files need to be installed from. This will often be an HTTP or FTP URL, but it can be a file-based URL as well.
When using a URL, two components are used. First, the URL identifies the protocol to be used and is in the format protocol://, such as http://, ftp://, or file://. Following the URL is the exact location on that URL. That can be the name of a web server or an FTP server, including the subdirectory where the files are found. If the URL is file based, the location on the file system starts with a / as well.
Therefore, for a file system-based URL, there will be three slashes in the baseurl, such as baseurl:///repo, which refers to the directory /repo on the local file system.
Understanding Repository Security
Using repositories allows you to transparently install software packages from the Internet. This is convenient, but it also involves a security risk. When installing RPM packages, you do that with root permissions, and if in the RPM package script code is executed (which is common), that is executed as root as well. For that reason, you want to make sure that you can trust the software packages you are trying to install. This is why repositories in general use keys for package signing. This is also why on Red Hat Enterprise Linux it is a good idea to use repositories provided though RHN only.
To secure packages in a repository, these packages are often signed with a GPG key. This makes it possible to check whether packages have been changed since the owner of the repository provided them. The GPG key used to sign the software packages is typically made available through the repository as well. The users of the repository can download that key and store it locally so that the package signature check can be performed automatically each time a package is downloaded from the repository.
If repository security is compromised and an intruder manages to hack the repository server and put some fake packages on it, the GPG key signature will not match, and the yum command will complain while installing new packages. This is why it is highly recommended to use GPG keys when using Internet repositories.
If you are using a repository where GPG package signing has been used, on first contact with that repository, the rpm command will propose to download the key that was used for package signing (see Example 9-2). This is a transparent procedure that requires no further action. The GPG keys that were used for package signing are installed to the /etc/pki/rpm-gpg directory by default.
Tip
For using internal repositories, the security risks are not that high. For that reason, you do not have to know how to work with GPG-signed packages on the exam.
Example 9-2 On First Contact with a Repository, the GPG Key Is Downloaded
[root@server1 ~]# yum install kernel Loaded plugins: fastestmirror Loading mirror speeds from cached hostfile * base: centos.mirror1.spango.com * extras: mirror.netrouting.net * updates: mirrors.supportex.net Resolving Dependencies --> Running transaction check ---> Package kernel.x86_64 0:4.10.0-229.1.2.el8 will be installed --> Processing Dependency: linux-firmware >= 20190911 for package: kernel-4.10.0-229.1.2.el7.x86_64 --> Running transaction check ---> Package linux-firmware.noarch 0:20140213-0.3.git4164c23.el8 will be updated ---> Package linux-firmware.noarch 0:20140911-0.1.git365e80c.el8 will be an update --> Finished Dependency Resolution Dependencies Resolved ======================================================================= ======================================================================= Package Arch Version Repository Size ======================================================================= Installing: kernel x86_64 3.10.0-229.1.2.el8 updates 31M Updating for dependencies: linux-firmware noarch 20190911-0.1.git365e80c.el8 base 17 M Transaction Summary ======================================================================= Install 1 Package Upgrade ( 1 Dependent package) Total size: 48 M Is this ok [y/d/N]: y Downloading packages: warning: /var/cache/yum/x86_64/8/base/packages/linux-firmware-20140911- 0.1.git365e80c.el7.noarch.rpm: Header V3 RSA/SHA256 Signature, key ID f4a80eb5: NOKEY Retrieving key from file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-8 Importing GPG key 0xF4A80EB5: Userid : "CentOS-8 Key (CentOS 7 Official Signing Key) <[email protected]>" Fingerprint: 6341 ab27 53d7 8a78 a7c2 7bb1 24c6 a8a7 f4a8 0eb5 Package : centos-release-8-0.1406.el7.centos.2.3.x86_64 (@anaconda) From : /etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-8 Is this ok [y/N]:y
Creating Your Own Repository
Creating your own repository is not a requirement for the RHCSA exam, but knowing how to do so is useful if you want to test setting up and working with repositories. Also, while doing the exercises in this book, it is important to know how to set up your own repositories, as you should not use the repositories that are available online.
Setting up your own repository allows you to put your own RPM packages in a directory and publish that directory as a repository. It is also useful to know how to do this if you have installed RHEL and not connected it to RHN, which means that you would not have any repositories at all.
The procedure itself is not hard to summarize. You need to make sure all RPM packages are available in the directory that you want to use as a repository, and after doing that, you need to use the createrepo command to generate the metadata that enables you to use that directory as a repository. Exercise 9-1 describes how to create your own repository.
Exercise 9-1 Creating Your Own Repository
To perform this exercise, you need to have access to the RHEL or CentOS installation disk or ISO file.
Insert the installation disk in your virtual machine and make sure it is attached and available.
Type mkdir /repo so that you have a mount point where you can mount the ISO file.
Add the following line to the end of the /etc/fstab configuration file: /dev/sr0 /repo iso9660 defaults 0 0
Type mount -a, followed by mount | grep sr0. You should now see that the optical device is mounted on the directory /repo. At this point, the directory /repo can be used as a repository.
At this point, two repositories are available through the /repo directory. The BaseOS repository provides access to the base packages, and the Application Stream (AppStream) repository provides access to application streams (these repositories are described in more detail in the “Managing Package Module Streams” section later in the chapter). To make them accessible, you need to add two files to the /etc/yum.repos.d directory. Start with the file BaseOS and give it the following contents:
[BaseOS] name=BaseOS baseurl=file:///repo/BaseOS gpgcheck=0
Next, add the file /etc/yum.repos.d/AppStream.repo with the following contents:
[AppStream] name=AppStream baseurl=file:///repo/AppStream gpgcheck=0
Type yum repolist to verify the availability of the newly created repository. It should show the name of the myrepo repository, including the number of packages offered through this repository (see Example 9-3). Notice that if you’re doing this on RHEL, you’ll also see a message that this system is not registered to Red Hat Subscription Management. You can safely ignore that message.
Example 9-3 Verifying Repository Availability with yum repolist
[root@server3 yum.repos.d]# yum repolist Updating Subscription Management repositories. Unable to read consumer identity This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register. AppStream 194 MB/s | 5.3 MB 00:00 BaseOS 86 MB/s | 2.2 MB 00:00 Last metadata expiration check: 0:00:01 ago on Sat 25 May 2019 09:20:19 AM EDT. repo id repo name status AppStream AppStream 4,672 BaseOS BaseOS 1,658
Using yum
At this point, you should have operational repositories, so it is time to start using them. To use repositories, you need the yum command. This command enables you to perform several tasks on the repositories. Table 9-3 provides an overview of common yum tasks.
Table 9-3 Common yum Tasks
Task |
Explanation |
|---|---|
search |
Search for the exact name of a package |
[what]provides */name |
Perform a deep search in the package to look for specific files within the package |
info |
Provide more information about the package |
install |
Install the package |
remove |
Remove the package |
list [all | installed] |
List all or installed packages |
group list |
List package groups |
group install |
Install all packages from a group |
update |
Update packages specified |
clean all |
Remove all stored metadata |
Using yum to Find Software Packages
To install packages with yum, you first need to know the exact name of the package. The yum search command can help you with that. When you use yum search, it first gets in touch with the online repositories (which might take a minute), after which it downloads the most recent repository metadata to the local machine. Then, yum search looks in the package name and description for the string you have been looking for. In Example 9-4, you can see what the result looks like after using yum search user.
Example 9-4 yum search Sample Output
[root@server3 ~]# yum search user Updating Subscription Management repositories. Unable to read consumer identity This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register. Last metadata expiration check: 0:02:23 ago on Sat 25 May 2019 09:20:19 AM EDT. ==================== Name & Summary Matched: user ==================== trouser s-lib.x86_64 : TrouSer S libtspi library trouser s-lib.i686 : TrouSer S libtspi library trouser s-lib.x86_64 : TrouSer S libtspi library gnome-user-docs.noarch : GNOME User Documentation gnome-user-docs.noarch : GNOME User Documentation xdg-user-dirs.x86_64 : Handles user special directories xdg-user-dirs.x86_64 : Handles user special directories util-linux-user.x86_64 : libuser based util-linux utilities ...
Because the yum search command looks in the package name and summary only, it often does not show what you need. You often need to look for packages containing a specific file. To do this, the yum whatprovides command or yum provides command will help you. (There is no functional difference between these two commands.) To make it clear that you are looking for packages containing a specific file, you need to specify the filename as */filename, or use the full path name to the file you want to use. So if you need to look for the package containing the file semanage, for example, use yum whatprovides */semanage. It will show the name of the package as a result. Try it, and compare the result to the result of the command yum search semanage; you’ll notice that it is quite different.
Getting More Information About Packages
Before installing a package, it is a good idea to get some more information about the package. Because the yum command was developed to be intuitive, it is almost possible to guess how that works. Just use yum info, followed by the name of the package. In Example 9-5, you see what this looks like for the nmap package (which, by the way, is a very useful tool). It is a network sniffer that allows you to find ports that are open on other hosts. Just use nmap 192.168.4.100 to give it a try, but be aware that some network administrators really do not like nmap and might consider this a hostile attack.
Example 9-5 Example Output of yum info nmap
[root@server3 ~]# yum info nmap
Updating Subscription Management repositories.
Unable to read consumer identity
This system is not registered to Red Hat Subscription Management.
You can use subscription-manager to register.
Last metadata expiration check: 0:05:01 ago on Sat 25 May 2019
09:20:19 AM EDT.
Available Packages
Name : nmap
Epoch : 2
Version : 7.70
Release : 4.el8
Arch : x86_64
Size : 5.8 M
Source : nmap-7.70-4.el8.src.rpm
Repo : AppStream
Summary : Network exploration tool and security scanner
URL : http://nmap.org/
License : Nmap
Description : Nmap is a utility for network exploration or security
auditing. It supports
: ping scanning (determine which hosts are up), many
port scanning techniques
: (determine what services the hosts are offering), and
TCP/IP fingerprinting
: (remote host operating system identification). Nmap
also offers flexible target
: and port specification, decoy scanning, determination
of TCP sequence
: predictability characteristics, reverse-identd
scanning, and more. In addition
: to the classic command-line nmap executable, the Nmap
suite includes a flexible
: data transfer, redirection, and debugging tool (netcat
utility ncat), a utility
: for comparing scan results (ndiff), and a packet
generation and response
: analysis tool (nping).
Installing and Removing Software Packages
If after looking at the yum info output you are happy with the package, the next step is to install it. As anything else you are doing with yum, it is not hard to guess how to do that: use yum install nmap. When used in this way, the yum command asks for confirmation. If when you type the yum install command you are sure about what you are doing, you might as well use the -y option, which passes a “yes” to the confirmation prompt that yum normally issues. Example 9-6 shows what the result looks like.
Example 9-6 Installing Software with yum
[root@server3 ~]# yum install nmap Updating Subscription Management repositories. Unable to read consumer identity This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register. Last metadata expiration check: 0:06:16 ago on Sat 25 May 2019 09:20:19 AM EDT. Dependencies resolved. ======================================================================= Package Arch Version Repository Size ======================================================================= Installing: nmap x86_64 2:7.70-4.el8 AppStream 5.8 M Transaction Summary ======================================================================= Install 1 Package Total size: 5.8 M Installed size: 24 M Is this ok [y/N]: y Downloading Packages: Running transaction check Transaction check succeeded. Running transaction test Transaction test succeeded. Running transaction Preparing : 1/1 Installing : nmap-2:7.70-4.el8.x86_64 1/1 Running scriptlet : nmap-2:7.70-4.el8.x86_64 1/1 Verifying : nmap-2:7.70-4.el8.x86_64 1/1 Installed products updated. Installed: nmap-2 :7.70-4.el8.x86_64 Complete!
In Example 9-6, you can see that yum starts by analyzing what is going to be installed. Once that is clear, it gives an overview of the package that is going to be installed, including its dependencies. Then, the package itself is installed to the system.
To remove software packages from a machine, use the yum remove command. This command also does a dependency analysis, which means that it will remove not only the selected package but also all packages that depend on it. This may sometimes lead to a long list of software packages that are going to be removed. To avoid unpleasant surprises, you should never use yum remove with the -y option.
Note
Some packages are protected. Therefore, you cannot easily remove them. If yum remove encounters protected packages, it refuses to remove them.
Showing Lists of Packages
When working with yum, you may also use the yum list command to show lists of packages. Used without arguments, yum list shows a list of all software packages that are available, including the repository they were installed from. You see the repository names as listed in Table 9-2 and the @anaconda repository as well. If a repository name is shown, the package is available in that specific repository. If @anaconda is listed, the package has already been installed on this system. Example 9-7 shows the partial output of the yum list command.
Example 9-7 Partial Output of the yum list Command
[root@server3 ~]# yum list | less Updating Subscription Management repositories. Unable to read consumer identity This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register. Last metadata expiration check: 0:09:31 ago on Sat 25 May 2019 09:20:19 AM EDT. Installed Packages GConf2.x86_64 3.2.6-22.el8 @AppStream ModemManager.x86_64 1.8.0-1.el8 @anaconda ModemManager-glib.x86_64 1.8.0-1.el8 @anaconda NetworkManager.x86_64 1:1.14.0-14.el8 @anaconda NetworkManager-adsl.x86_64 1:1.14.0-14.el8 @anaconda NetworkManager-bluetooth.x86_64 1:1.14.0-14.el8 @anaconda NetworkManager-config-server.noarch 1:1.14.0-14.el8 @anaconda NetworkManager-libnm.x86_64 1:1.14.0-14.el8 @anaconda NetworkManager-team.x86_64 1:1.14.0-14.el8 @anaconda NetworkManager-tui.x86_64 1:1.14.0-14.el8 ...
If you want to see which packages are installed on your server, you can use the yum list installed command. The yum list command can also prove useful when used with the name of a specific package as its argument. For instance, type yum list kernel to show which version of the kernel is actually installed and which version is available as the most recent version in the repositories. Example 9-8 shows the result of this command.
Example 9-8 Use yum list packagename for Information About Installed and Available Versions
[root@server3 ~]# yum list kernel Updating Subscription Management repositories. Unable to read consumer identity This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register. Last metadata expiration check: 0:11:57 ago on Sat 25 May 2019 09:20:19 AM EDT. Installed Packages kernel.x86_64 4.18.0-80.el8 @anacond
Updating Packages
One of the major benefits of working with yum repositories is that repositories make it easy to update packages. The individual who maintains a repository is responsible for copying updated packages to the repositories. The index in the repository always contains the current version of a package in the repository. On the local machine also, a database is available with the current versions of the packages that are used. When using the yum update command, current versions of packages that are installed are compared to the version of these packages in the repositories. As shown in Example 9-9, yum next shows an overview of updatable packages. From this overview, type y to install the updates.
Notice that while updating packages the old version of the package is replaced with a newer version of the package. There is one exception, which is for the kernel package. Even if you are using the yum update kernel command, the kernel package is not updated, but the newer kernel is installed beside the old kernel, so that while booting you can select the kernel that you want to use. This is useful if the new kernel won’t work because of hardware compatibility issues. In that case, you can interrupt the GRUB 2 boot process (see Chapter 17, “Managing and Understanding the Boot Procedure,” for more details) to start the older kernel.
Example 9-9 Using yum update
[root@server1 ~]# yum update kernel
Updating Subscription Management repositories.
Red Hat Enterprise Linux 8 for x86_64 - AppStream (RPMs)
2.4 kB/s | 4.5 kB 00:01
Red Hat Enterprise Linux 8 for x86_64 - BaseOS (RPMs)
2.5 kB/s | 4.0 kB 00:01
created by dnf config-manager from file:///repo
0.0 B/s | 0 B 00:00
Failed to synchronize cache for repo 'repo', ignoring this repo.
Dependencies resolved.
======================================================================
Package Arch Version Repository Size
======================================================================
Installing:
kernel x86_64 4.18.0-80.1.2.el8_0 rhel-8-for-x86_
64-baseos-rpms 406 k
Installing dependencies:
kernel-modules x86_64 4.18.0-80.1.2.el8_0 rhel-8-for-x86_
64-baseos-rpms 20 M
kernel-core x86_64 4.18.0-80.1.2.el8_0 rhel-8-for-x86_
64-baseos-rpms 24 M
Transaction Summary
======================================================================
Install 3 Packages
Total download size: 44 M
Installed size: 76 M
Is this ok [y/N]:y
Working with yum Package Groups
While managing specific services on a Linux machine, you often need several different packages. If, for instance, you want to make your machine a virtualization host, you need the KVM packages, but also all supporting packages such as qemu, libvirt, and the client packages. Or while configuring your server as a web server, you need to install additional packages like PHP as well in many cases.
To make it easier to manage specific functionality, instead of specific packages, you can work with package groups as well. A package group is defined in the repository, and yum offers the group management commands to work with these groups. For an overview of all current groups, use yum groups list. This shows output as in Example 9-10.
Tip
The name of the command is yum groups, but there are aliases that ensure that yum group and even commands like yum groupinstall are also working. So, you can use either of these commands.
Example 9-10 Showing Available yum Groups
[root@server1 ~]# yum groups list Updating Subscription Management repositories. created by dnf config-manager from file:///repo 0.0 B/s | 0 B 00:00 Failed to synchronize cache for repo 'repo', ignoring this repo. Last metadata expiration check: 0:01:08 ago on Sat 25 May 2019 09:34:12 AM EDT. Available Environment Groups: Server Minimal Install Workstation Virtualization Host Custom Operating System Installed Environment Groups: Server with GUI Installed Groups: Container Management Headless Management Available Groups: RPM Development Tools Smart Card Support .NET Core Development Network Servers Development Tools System Tools Graphical Administration Tools Scientific Support Security Tools Legacy UNIX Compatibility
Notice that some yum groups are not listed by default. To show those as well, type yum groups list hidden. You see that the list of groups that is displayed is considerably longer. The difference is that yum groups list shows environment groups, which contain basic functionality. Within an environment group, different subgroups can be used; these are displayed only when using yum groups list hidden.
To get information about packages available in a group, you use yum groups info. Because group names normally contain spaces, do not forget to put the entire group name between quotes. So, type yum groups info "Basic Web Server" to see what is in the Basic Web Server group. As you can see in Example 9-11, this command shows mandatory items and optional items in the group. The items can be groups and individual packages.
Example 9-11 Showing Group Contents with yum groups info
[root@server1 ~]# yum groups info "Basic Web Server" Updating Subscription Management repositories. created by dnf config-manager from file:///repo 0.0 B/s | 0 B 00:00 Last metadata expiration check: 0:02:55 ago on Sat 25 May 2019 09:34:12 AM EDT. Group: Basic Web Server Description: These tools allow you to run a Web server on the system. Mandatory Packages: httpd Default Packages: httpd-manual mod_fcgid mod_ssl Optional Packages: libmemcached memcached mod_auth_gssapi mod_security mod_security-mlogc mod_security_crs
Using yum History
While working with YUM, all actions are registered. You can use the yum history command to get an overview of all actions that have been issued. From the history file, it is possible to undo specific actions; use yum history undo followed by the number of the specific action you want to undo.
In Example 9-12, you see the result of the yum history command, where every action has its own ID.
Example 9-12 Showing Past yum Actions Using yum history
[root@server1 ~]# yum history Updating Subscription Management repositories. ID | Command line | Date and time | Action(s)| Altered ---------------------------------------------------------------------- 3 | install dnf-utils | 2019-05-25 09:07 | Install | 1 2 | install stratis-cli stra | 2019-05-24 07:13 | Install | 9 1 | | 2019-05-19 06:20 | Install | 1336 EE
As you can see, action number 2 altered nine packages and was used to install packages. To undo this action completely, type yum history undo 2. In Exercise 9-2, you apply some of the most useful yum commands for common package management tasks, as discussed previously.
Exercise 9-2 Using yum for Package Management
Type yum repolist to show a list of the current repositories that your system is using.
Type yum search seinfo. This will give no matching result.
Type yum provides */seinfo. The command shows that the setools-console- <version> package contains this file.
Install this package using yum install -y setools-console. Depending on your current configuration, you might notice that quite a few dependencies have to be installed also.
Type yum list setools-console. You see that the package is listed as installed.
Type yum history and note the number of the last yum command you used.
Type yum history undo <nn> (where <nn> is replaced with the number that you found in step 6). This undoes the last action, so it removes the package you just installed.
Repeat the yum list setools-console command. The package is now listed as available but not as installed.
Managing Package Module Streams
In RHEL 8, Red Hat has introduced Package Module Streams. In previous versions of RHEL, it was difficult to work with different versions of packages. For instance, RHEL 7 has always provided Python 2.x as the default Python version, even though Python 3.x was already available. Using a different version of user-space packages like Python was very difficult, as different repositories had to be added to offer Python 3 instead, which on its turn would again create problems for users who would rather use an older version of Python. In RHEL 8 different versions of the same package can be offered using Package Module Streams. Also, Package Module Streams make it possible to update critical applications more frequently than the base operating system is updated.
To separate core operating system packages from user-space packages, RHEL 8 provides two main repositories, referenced earlier: BaseOS and Application Stream. In BaseOS you’ll find core operating system packages as RPM packages. The life cycle of these packages is comparable to the life cycle of previous RHEL versions.
Understanding Modules
In the Application Stream repository, content with varying life cycles is provided. This content is provided as the traditional RPM packages, but also as modules. A module describes a set of RPM packages that belong together. Typically, modules are organized around a specific version of an application, and in a module you’ll find module packages, together with all of the dependencies for that specific version.
Each module can have one or more application streams. A stream contains one specific version, and updates are provided for a specific stream. When working with modules that have different streams, only one stream can be enabled at the same time.
Modules can also have one or more profiles. A profile is a list of packages that are installed together for a particular use case. You may find, for instance, a minimal profile, a default profile, a server profile. and many more. While working with modules, you may select which profile you want to use. Table 9-4 provides an overview of key terminology when working with modules.
Table 9-4 YUM Module Terminology
Item |
Explanation |
|---|---|
RPM |
The default package format. Contains files, as well as metadata that describes how to install the files. Optionally may contain pre- and post-installation scripts as well. |
Module |
A delivery mechanism to install RPM packages. In a module different versions and profiles can be provided. |
Application stream |
A specific version of the module. |
Profile |
A collection of packages that are installed together for a particular use case. |
Managing Modules
The yum command in RHEL 8 supports working with modules using the yum module command. To find out which modules are available, you may want to start with the yum module list command. You can see its sample output in Example 9-13.
Example 9-13 Showing Yum Modules with yum module list
[root@server3 ~]# yum module list
Updating Subscription Management repositories.
Unable to read consumer identity
This system is not registered to Red Hat Subscription Management.
You can use subscription-manager to register.
Last metadata expiration check: 0:21:12 ago on Sat 25 May 2019
09:36:47 AM EDT.
AppStream
Name Stream Profiles Summary
389-ds 1.4 389 Directory Server
(base)
ant 1.10 [d] common [d] Java build tool
container-tools 1.0 common [d] Common tools and
dependencies for
container runtimes
container-tools rhel8 [d][e] common [d] Common tools and
dependencies for
container runtimes
freeradius 3.0 [d] server [d] High-performance and
highly configurable
free RADIUS server
gimp 2.8 [d] common [d], devel gimp module
go-toolset rhel8 [d] common [d] Go
httpd 2.4 [d] common [d], devel Apache HTTP Server
, minimal
idm DL1 common [d], adtru The Red Hat
Enterprise Linux Identity
Managest, client, dns, ment
system module server
idm client [d] common [d] RHEL IdM long term
support client module
inkscape 0.92.3 [d] common [d] Vector-based drawing
program using SVG
javapackages-runtime 201801 [d] common [d] Basic runtime
utilities to
support Java
applications
...
pki-core 10.6 PKI Core
pki-deps 10.6 PKI Dependencies
postgresql 10 [d] client, server [d] PostgreSQL server
and client module
postgresql 9.6 client, server [d] PostgreSQL server
and client module
python27 2.7 [d] common [d] Python programming
language, version
2.7
python36 3.6 [d][e] common [d], build Python programming
language, version
3.6
redis 5 [d] common [d] Redis persistent
key-value database
rhn-tools 1.0 [d] common [d] Red Hat Satellite
5 tools for RHEL
ruby 2.5 [d] common [d] An interpreter of
object-oriented
scripting language
rust-toolset rhel8 [d] common [d] Rust
satellite-5-client 1.0 [d][e] common [d], gui Red Hat Satellite
5 client packages
scala 2.10 [d] common [d] A hybrid
functional/object-
oriented language
for the JVM
squid 4 [d] common [d] Squid - Optimising
Web Delivery
subversion 1.10 [d] common [d], Apache Subversion
server
swig 3.0 [d] common [d], Connects C/C++/
complete Objective C to
some high-level
programming
languages
varnish 6 [d] common [d] Varnish HTTP cache
virt rhel [d][e] common [d] Virtualization
module
Hint: [d]efault, [e]nabled, [x]disabled, [i]nstalled
In the list of modules, you can see whether or not the module is installed and whether or not a specific stream is enabled. To list specific streams for a module, use the yum module list modulename command. For instance, use yum module list perl to get details about streams that are available for the Perl module, as shown in Example 9-14.
Example 9-14 Showing Details About YUM Modules with yum module list
[root@server3 ~]# yum module list perl Updating Subscription Management repositories. Unable to read consumer identity This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register. Last metadata expiration check: 0:26:17 ago on Sat 25 May 2019 09:36:47 AM EDT. AppStream Name Stream Profiles Summary perl 5.24 common [d], minimal Practical Extraction and Report Language perl 5.26 [d] common [d], minimal Practical Extraction and Report Language Hint: [d]efault, [e]nabled, [x]disabled, [i]nstalled
After finding out which module streams are available, the next step is to get information about specific profiles. You can use yum module info to obtain this information. For instance, use yum module info perl to get more information about the Perl module. This will provide information for profiles that are available in all the module streams. To find profile information for a specific stream, you can provide the stream version as an argument. For instance, use yum module info perl:5.26 (see Example 9-15).
Example 9-15 Showing Information About YUM Modules with yum module list
[root@server3 ~]# yum module info perl:5.26
Updating Subscription Management repositories.
Unable to read consumer identity
This system is not registered to Red Hat Subscription Management.
You can use subscription-manager to register.
Last metadata expiration check: 0:29:59 ago on Sat 25 May 2019
09:36:47 AM EDT.
Name : perl
Stream : 5.26 [d][a]
Version : 820181219174508
Context : 9edba152
Profiles : common [d], minimal
Default profiles : common
Repo : AppStream
Summary : Practical Extraction and Report Language
Description : Perl is a high-level programming language with
roots in C, sed, awk and shell scripting. Perl
is good at handling processes and files, and is
especially good at handling text. Perl's
hallmarks are practicality and efficiency.
While it is used to do a lot of different
things, Perl's most common applications
are system administration utilities and web
programming.
Hint: [d]efault, [e]nabled, [x]disabled, [i]nstalled, [a]ctive]
After finding module information, the next step is to enable a module stream and install modules. Every module has a default module stream, providing access to a specific version. If that version is what you need, you don’t have to enable anything. If you want to work with a different version, you should start by enabling the corresponding module stream. For example, type yum module enable perl:5.24 to enable that specific version.
Enabling a module stream before starting to work with a specific module is not mandatory. If you just use yum module install to install packages from a module, packages from the default module stream will be installed. You can also switch between application stream versions. If, for instance, you are now on php:7.1 and you want to change to php:7.2, you just have to type yum module install php:7.2. This will disable the old stream and enable the new stream. After doing this, to ensure that all dependent packages that are not in the module itself are updated as well, you should type yum distro-sync to finalize the procedure.
In Exercise 9-3 you can practice working with Yum modules in RHEL 8.
Exercise 9-3 Working with Modules
Type yum module list. You’ll see a list of all modules that are available.
Type yum module provides httd. This will show you that the httpd package is a part of the httpd module. As this module has just one stream, we’ll have a look at the PHP module in the next steps in this exercise.
Type yum module info php to get information about the php module. This gives information about the default PHP application stream.
To investigate packages in the application stream for PHP 7.1, type yum module info --profile 7.1.
Type yum module install php:7.1/devel. This will install PHP from the PHP 7.1 application stream, using the developer profile. Notice that by installing it from this specific stream, you’ll also enable the 7.1 application stream.
Type yum module install php:7.2 to switch to the newer version of the PHP module.
To ensure that all dependent packages are updated as well, type yum distro-sync.
Managing Software Packages with rpm
Once upon a time, repositories did not exist, and the rpm command was used to install package files after they had been downloaded. That worked, but there was one major issue: the dependency hell. Because RPM packages have always focused on specific functionality, to install specific software, a collection of RPM packages was normally required. Therefore, a “missing dependency” message was often issued while users were trying to install RPM packages, which meant that to install the selected package, other packages needed to be installed first. Sometimes a whole chain of dependencies needed to be installed to finally get the desired functionality. That did not make working with RPM packages a joyful experience.
On modern RHEL systems, repositories are used, and packages are installed using yum. The yum command considers all package dependencies and tries to look them up in the currently available repositories. On a RHEL system configured to get updates from RHN, or on a CentOS system where consistent repositories are used, the result is that package installation nowadays is without problems and the rpm command no longer is needed for software installation.
Even after downloading an RPM package file, you do not need to use the rpm -Uvh packagename command anymore to install it (even if it still works). A much better alternative is yum install packagename, which installs the package and also considers the repositories to resolve dependencies automatically. (In earlier versions of RHEL, the yum localinstall command was used to do this; in RHEL 8, yum localinstall is deprecated.) That does not mean the rpm command has become totally useless. You can still use it to query RPM packages.
Tip
On your system, two package databases are maintained: the YUM database and the RPM database. When you are installing packages through yum, the YUM database is updated first, after which the updated information is synchronized to the RPM database. If you install packages using the rpm command, the update is written to the RPM database only and will not be updated to the YUM database, which is an important reason not to use the rpm command anymore to install software packages.
Understanding RPM Filenames
When working with RPM packages directly, it makes sense to understand how the RPM filename is composed. A typical RPM filename looks like autofs-5.0.7- 40.el7.x86_64.rpm. This name consists of several parts:
autofs: The name of the actual package.
5.0.7: The version of the package. This normally corresponds to the name of the package as it was released by the package creator.
-40: The subversion of the package.
el7: The Red Hat version this package was created for.
x86_64: The platform (32 bits or 64 bits) this package was created for.
Querying the RPM Database
The rpm command enables you to get much information about packages. Using RPM queries can be a really useful way to find out how software can be configured and used. To start, you can use the rpm -qa command. Like yum list installed, this shows a list of all software that is installed on the machine. Use grep on this command to find out specific package names. To perform queries on RPM packages, you just need the name and not the version information.
After finding the package about which you want to have more information, you can start with some generic queries to find out what is in the package. In the following examples, I assume that you are using RPM queries on the nmap RPM package. To start, type rpm -qi nmap to get a description of the package. This will perform a query of a package that is already installed on your system, and it will query the package database to get more details about it.
The next step is to use rpm -ql nmap, which shows a list of all files that are in the package. On some packages, the result can be a really long list of filenames that is not particularly useful. To get more specific information, use rpm -qd nmap, which shows all documentation available for the package, or rpm -qc nmap, which shows all configuration files in the package.
Using RPM queries can really help in finding out more useful information about packages. The only thing that you need to know is the RPM package name that a specific file belongs to. To find this, use rpm -qf, followed by the specific filename you are looking for. Use, for instance, rpm -qf /bin/ls to find the name of the RPM package the ls command comes from. In upcoming Exercise 9-4, you’ll see how useful it can be to use RPM queries in this way.
Querying RPM Package Files
RPM queries by default are used on the RPM database, and what you are querying are installed RPM packages. It sometimes makes sense to query an RPM package file before actually installing it. To do this, you need to add the -p option to the query, because without the -p option, you will be querying the database, not the package file. Also, when querying a package file, you need to refer to the complete filename, including the version number and all other information that you do not have to use when querying the RPM database. As an example, the rpm -qp --scripts httpd-2.4.6-19.el7.centos.x86_64.rpm command queries the specific RPM file to see whether it contains scripts.
A query option that needs special attention is --scripts, which queries an RPM package or package file to see which scripts it contains (if any). This option is especially important when combined with the -p option, to find out whether a package file that you are going to install includes any scripts.
When you install RPM packages, you do so as root. Before installing an RPM package from an unknown source, you need to make sure that it does not include any rogue scripts. If you do not, you risk installing malware on your computer without even knowing it.
Table 9-5 describes the most important RPM querying options.
Table 9-5 Common RPM Query Commands
Command |
Use |
|---|---|
rpm -qf |
Uses a filename as its argument to find the specific RPM package a file belongs to. |
rpm -ql |
Uses the RPM database to provide a list of files in the RPM package. |
rpm -qi |
Uses the RPM database to provide package information (equivalent to yum info). |
rpm -qd |
Uses the RPM database to show all documentation that is available in the package. |
rpm -qc |
Uses the RPM database to show all configuration files that are available in the package. |
rpm -q --scripts |
Uses the RPM database to show scripts that are used in the package. This is particularly useful if combined with the -p option. |
rpm -qp <pkg> |
The -p option is used with all the previously listed options to query individual RPM package files instead of the RPM package database. Using this option before installation helps you find out what is actually in the package before it is installed. |
rpm -qR |
Shows dependencies for a specific package. |
rpm -V |
Shows which parts of a specific package have been changed since installation. |
rpm -Va |
Verifies all installed packages and shows which parts of the package have been changed since installation. This is an easy and convenient way to do a package integrity check. |
rpm -qa |
Lists all packages that are installed on this server. |
Using repoquery
While rpm -qp provides useful tools to query packages before installation, there is a slight problem with this command: It works only on RPM package files, and it cannot query files directly from the repositories. If you want to query packages from the repositories before they have been installed, you need repoquery. This binary is not installed by default, so make sure to install the yum-utils RPM package to use it.
The repoquery command is pretty similar to the rpm -q command and uses many similar options. There is just one significant option missing: --script. A simple solution is to make sure that you are using trusted repositories only, to prevent installing software that contains dangerous script code.
If you need to thoroughly analyze what an RPM package is doing when it is installed, you can download it to your machine, which allows you to use the rpm -qp --scripts command on the package. To download a package from the repository to the local directory, you can use the yumdownloader command, which comes from the yum-utils package.
Now that you have learned all about RPM querying options, you can practice these newly acquired skills in Exercise 9-4 to get more information about software that is installed on your RHEL system.
Exercise 9-4 Using RPM Queries
Type which dnsmasq. This command gives the complete path name of the dnsmasq command.
Type rpm -qf $(which dnsmasq). This will do an RPM file query on the result of the which dnsmasq command; you learn more about this technique in Chapter 19, “An Introduction to Bash Shell Scripting.”
Now that you know that the dnsmasq binary comes from the dnsmasq package, use rpm -qi dnsmasq to show more information about the package.
The information that is shown with rpm -qi is useful, but it does not give the details that are needed to start working with the software in the package. Use rpm -ql dnsmasq to show a list of all files in the package.
Use rpm -qd dnsmasq to show the available documentation. Notice that this command reveals that there is a man page, but there is also a doc.html file and a setup.html file in the /usr/share/doc/dnsmasq-version directory. Open these files with your browser to get more information about the use of dnsmasq.
Type rpm -qc dnsmasq to see which configuration files are used by dnsmasq.
After installation, it does not make much sense, but it is always good to know which scripts are executed when a package is installed. Use rpm -q --scripts dnsmasq to show the script code that can be executed from this RPM.
Tip
Working with RPM queries is an extremely valuable skill on the RHCSA exam. If you know how to handle queries, you can find all relevant configuration files and the documentation.
Summary
In this chapter, you learned how to work with software on Red Hat Enterprise Linux. You learned how to use yum to manage software packages coming from repositories. You also learned how to use the rpm command to perform queries on the packages on your system. Make sure that you master these essential skills well; they are key to getting things done on Red Hat Enterprise Linux.
Exam Preparation Tasks
As mentioned in the section “How to Use This Book” in the Introduction, you have several choices for exam preparation: the end-of-chapter labs; the memory tables in Appendix B; Chapter 26, “Final Preparation”; and the practice exams.
Review All Key Topics
Review the most important topics in the chapter, noted with the Key Topic icon in the outer margin of the page. Table 9-6 lists a reference of these key topics and the page number on which each is found.
Table 9-6 Key Topics for Chapter 9
Key Topic Element |
Description |
Page |
|---|---|---|
Paragraph |
Description of how to create a repository |
|
Common yum tasks |
||
List |
RPM package name components |
|
Common RPM query commands |
Complete Tables and Lists from Memory
Print a copy of Appendix B, “Memory Tables” (found on the companion website), or at least the section for this chapter, and complete the tables and lists from memory. Appendix C, “Memory Tables Answer Key,” includes completed tables and lists to check your work.
Define Key Terms
Define the following key terms from this chapter and check your answers in the glossary:
Review Questions
The questions that follow are meant to help you test your knowledge of concepts and terminology and the breadth of your knowledge. You can find the answers to these questions in Appendix A.
1. You have a directory containing a collection of RPM packages and want to make that directory a repository. Which command enables you to do that?
2. What needs to be in the repository file to point to a repository on http://server.example.com/repo?
3. You have just configured a new repository to be used on your RHEL computer. Which command enables you to verify that the repository is indeed available?
4. Which command enables you to search the RPM package containing the file useradd?
5. Which two commands do you need to use to show the name of the yum group that contains security tools and shows what is in that group?
6. Which command do you use to ensure that all PHP-related packages are going to be installed using the older version 5.1, without actually installing anything yet?
7. You want to make sure that an RPM package that you have downloaded does not contain any dangerous script code. Which command enables you to do so?
8. Which command reveals all documentation in an RPM package?
9. Which command shows the RPM package a file comes from?
10. Which command enables you to query software from the repository?
End-of-Chapter Labs
In these end-of-chapter labs, you use some of the essential RHEL package management skills. All assignments can be done on one server.
Lab 9.1
1. Copy some RPM files from the installation disk to the /myrepo directory. Make this directory a repository and make sure that your server is using this repository.
2. List the repositories currently in use on your server.
3. Search for the package that contains the cache-only DNS name server. Do not install it yet.
4. Perform an extensive query of the package so that you know before you install it which files it contains, which dependencies it has, and where to find the documentation and configuration.
5. Check whether the RPM package contains any scripts. You may download it, but you may not install it yet; you want to know which scripts are in a package before actually installing it, right?
6. Install the package you have found in step 3.
7. Undo the installation.
Lab 9.2
1. Find out which application streams are available for the Perl module.
2. Install Perl from the latest application stream version, using the most minimal installation option.
3. Downgrade, such that the previous version of the Perl application will be used from now on.
4. Ensure that all dependent packages on your system are downgraded as well.