Details About Red Hat YUM

Yum is the Red Hat package manager that is able to query for information about available packages, fetch packages from repositories, install and uninstall them, and update an entire system to the latest available version. Yum performs automatic dependency resolution on packages you are updating, installing, or removing, and thus is able to automatically determine, fetch, and install all available dependent packages.

Yum can be configured with new, additional repositories, or package sources, and also provides many plug-ins which enhance and extend its capabilities. Yum is able to perform many of the same tasks thatRPM can; additionally, many of the command line options are similar. Yum enables easy and simple package management on a single machine or on groups of them.

Yum also enables you to easily set up your own repositories of RPM packages for download and installation on other machines.

Checking For Updates

To see which installed packages on your system have updates available, use the following command:

yum check-update

Updating Packages

You can choose to update a single package, multiple packages, or all packages at once. If any dependencies of the package (or packages) you update have updates available themselves, then they are updated too.

Updating a Single Package

To update a single package, run the following command as root:

yum update package_name

Updating All Packages and Their Dependencies

To update all packages and their dependencies, simply enter yum update (without any arguments):

yum update

Searching Packages

You can search all RPM package names, descriptions and summaries by using the following command:

yum search term…

 Listing Packages

yum list and related commands provide information about packages, package groups, and repositories.

All of Yum's list commands allow you to filter the results by appending one or more glob expressions as arguments. Glob expressions are normal strings of characters which contain one or more of the wildcard characters * (which expands to match any character multiple times) and ? (which expands to match any one character).

yum list glob_expression…

yum list all

Lists all installed and available packages.

yum list installed

Lists all packages installed on your system. The rightmost column in the output lists the repository from which the package was retrieved.

yum grouplist

Lists all package groups.

yum repolist

Lists the repository ID, name, and number of packages it provides for each enabled repository.

Displaying Package Information

To display information about one or more packages (glob expressions are valid here as well), use the following command:

yum info package_name…

Installing Packages

Yum allows you to install both a single package and multiple packages, as well as a package group of your choice.

Installing Individual Packages

To install a single package and all of its non-installed dependencies, enter a command in the following form:

yum install package_name

You can also install multiple packages simultaneously by appending their names as arguments:

yum install package_name package_name…

Installing a Package Group

A package group is similar to a package: it is not useful by itself, but installing one pulls a group of dependent packages that serve a common purpose. A package group has a name and a groupid. The yum grouplist -v command lists the names of all package groups, and, next to each of them, their groupid in parentheses. The groupid is always the term in the last pair of parentheses, such as kde-desktopin the following example:

~]# yum -v grouplist kde\*

You can install a package group by passing its full group name (without the groupid part) to groupinstall:

yum groupinstall group_name

You can also install by groupid:

yum groupinstall groupid

You can even pass the groupid (or quoted name) to the install command if you prepend it with an @-symbol (which tells yum that you want to perform a groupinstall):

yum install @group

For example, the following are alternative but equivalent ways of installing the KDE Desktop group:

~]# yum groupinstall "KDE Desktop"

~]# yum groupinstall kde-desktop

~]# yum install @kde-desktop

Removing Packages

Similarly to package installation, Yum allows you to uninstall (remove in RPM and Yum terminology) both individual packages and a package group.

Removing Individual Packages

To uninstall a particular package, as well as any packages that depend on it, run the following command as root:

yum remove package_name…

As when you install multiple packages, you can remove several at once by adding more package names to the command. For example, to remove totem, rhythmbox, and sound-juicer, type the following at a shell prompt:

~]# yum remove totem rhythmbox sound-juicer

Similar to install, remove can take these arguments:

•            package names
•           glob expressions
•           file lists
•           package provides

Setting [repository] Options

The [repository] sections, where repository is a unique repository ID such as my_personal_repo (spaces are not permitted), allow you to define individual Yum repositories.

The following is a bare-minimum example of the form a [repository] section takes:

[repository]

name=repository_name

baseurl=repository_url

Every [repository] section must contain the following directives:

name=repository_name

…where repository_name is a human-readable string describing the repository.

baseurl=repository_url

…where repository_url is a URL to the directory where the repodata directory of a repository is located:

o  If the repository is available over HTTP, use: http://path/to/repo

o  If the repository is available over FTP, use: ftp://path/to/repo

o  If the repository is local to the machine, use: file:///path/to/local/repo

o  If a specific online repository requires basic HTTP authentication, you can specify your username and password by prepending it to the URL as username:password@link. For example, if a repository on http://www.example.com/repo/ requires a username of “user” and a password of “password”, then the baseurl link could be specified ashttp://user:password@www.example.com/repo/.

Usually this URL is an HTTP link, such as:

baseurl=http://path/to/repo/releases/$releasever/server/$basearch/os/

Note that Yum always expands the $releasever, $arch, and $basearch variables in URLs. For more information about Yum variables,

Another useful [repository] directive is the following:

enabled=value

…where value is one of:

0 — Do not include this repository as a package source when performing updates and installs. This is an easy way of quickly turning repositories on and off, which is useful when you desire a single package from a repository that you do not want to enable for updates or installs.

1 — Include this repository as a package source.

Turning repositories on and off can also be performed by passing either the --enablerepo=repo_name or --disablerepo=repo_name option to yum, or through the Add/Remove Softwarewindow of the PackageKit utility.

Yum provides secure package management by enabling GPG (Gnu Privacy Guard; also known as GnuPG) signature verification on GPG-signed packages to be turned on for all package repositories (i.e. package sources), or for individual repositories. When signature verification is enabled, Yum will refuse to install any packages not GPG-signed with the correct key for that repository. This means that you can trust that the RPM packages you download and install on your system are from a trusted source, such as Red Hat, and were not modified during transfer.