1. Introduction

The RPM Package Management system comprises low-level and high-level tools. While we might not be able to work without the former, the latter are non-critical and can vary. For instance, we can have yum, dnf, or even custom solutions. In particular, the yum (Yellowdog Update Modified) command is a high-level package manager, now often just a symbolic link to dnf (Dandified YUM), its successor. Still, as the main way to manage the software in a Linux environment, caution should be exercised when manipulating the package installation system.

In this tutorial, we discuss ways to safely reinstall yum and its successor – dnf. First, we go over the original yum uninstall, download, and install. After that, we cover the same procedure for Dandified YUM (dnf).

We tested the code in this tutorial on CentOS 7 with GNU Bash 4.2.46 and YUM (Yellowdog Updater Modified) 3.4.3, as well as CentOS Stream 9 with GNU Bash 5.1.8 and DNF (DaNdiFied YUM) 4.14.0. It should work in most POSIX-compliant environments unless otherwise specified.

2. Reinstall Original Yellowdog Update Modified YUM

The original yum package manager is now of limited use. In fact, only older versions of most distributions still use the original YUM:

Actually, it’s not recommended to use the original YUM on newer distributions due to its flaws:

  • minimal API documentation
  • very slow dependency resolutions
  • excessive memory consumption
  • stops on unresponsive repositories
  • leaves unnecessary packages even if no package depends on them
  • protects kernel packages
  • overall poor performance

Still, we might need to install, remove, or reinstall the original yum when using an older Linux operating system (OS).

2.1. Verify Original YUM Installation

Since package managers usually ship with the distribution, let’s assume we already have the original yum installed:

$ yum list installed yum
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
 * base: centos.uni-sofia.bg
 * extras: centos.uni-sofia.bg
 * updates: centos.uni-sofia.bg
Installed Packages
yum.noarch            3.4.3-168.el7.centos            @anaconda

In this case, yum itself, with its list option, shows us that we seem to have version 3.4.3-168 installed. While this query returns a package and version, it doesn’t perform a check for the consistency of the installation.

However, we can verify a package via the low-level rpm command and its –verify or -V flag:

$ rpm --verify yum

No output should mean the package installation is as expected. Still, we could experience issues that necessitate a reinstall.

2.2. Acquire Original YUM Package

Before making changes to the current installation, it’s good to have the packages that we may later need handy.

As long as we don’t have critical problems, we can employ yum to find and download its own installation RPM.

First, we install the yum-utils package:

$ yum install yum-utils

After that, we leverage the yumdownloader utility to get the RPM file of yum:

$ yumdownloader yum
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
 * base: centos.uni-sofia.bg
 * extras: centos.uni-sofia.bg
 * updates: centos.uni-sofia.bg
yum-3.4.3-168.el7.centos.noarch.rpm       | 1.2 MB   00:00

On the other hand, we might not be able to access a current high-level package manager due to a corrupt installation. While we could check under the /var/cache/yum path for the yum package installation RPM, it most probably won’t be there since that cache is cleaned fairly often.

Because of this, it’s usually best to search for the correct package from the original distribution repository site. For example, the packages for CentOS 7 are at http://mirror.centos.org/centos/7/os/x86_64/Packages. So, we can employ curl and grep to query for the package:

$ curl --silent http://mirror.centos.org/centos/7/os/x86_64/Packages/ | grep 'yum-3.4.3'
[...]<a href="yum-3.4.3-168.el7.centos.noarch.rpm">yum-3.4.3-168.el7.centos.noarch.rpm</a>[...]

Because we know the package version and the naming format, we located the http://mirror.centos.org/centos/7/os/x86_64/Packages/yum-3.4.3-168.el7.centos.noarch.rpm package directly. Unlike with DNF YUM, it’s relatively hard to get the wrong version of the original YUM since its development is halted and distribution repositories already have only one version – the latest. Still, caution is advised.

Next, let’s download and save it locally with its –remote-name (-O):

$ curl --silent http://mirror.centos.org/centos/7/os/x86_64/Packages/yum-3.4.3-168.el7.centos.noarch.rpm --remote-name

Now, we have the original yum RPM package. We can proceed by removing our installation and performing a reinstall.

2.3. Uninstall Original YUM

Sometimes, we might want to remove even the package manager from a system. In fact, many reasons can lead to this:

  • change package manager
  • upgrade package manager, i.e., with dnf
  • corruption of the package manager installation
  • security
  • creating static OS images

When it comes to the original yum, we usually only need to employ the lower-level RPM management:

$ rpm --erase yum
error: Failed dependencies:
        yum >= 3.0 is needed by (installed) yum-plugin-fastestmirror-1.1.31-54.el7_8.noarch

In this case, we use the –erase or -e option of rpm to remove the package. However, we get an error at the dependency check, which states yum-plugin-fastestmirror as a dependency of yum.

To get a full list of packages dependent on yum and yum-plugin-fastestmirror, we can use the –query or -q option with the –whatrequires flag of rpm:

$ rpm --query --whatrequires yum
$ rpm --query --whatrequires yum-plugin-fastestmirror

Now, we know that these two packages are interdependent, so we can remove yum with the –nodeps flag to ignore any dependency conflicts:

$ which yum
$ rpm --erase --nodeps yum
$ which yum
/usr/bin/which: no yum in (/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin)

No output should mean we were successful. At this point, the yum command is no longer available.

2.4. Install or Reinstall Original YUM

After downloading the relevant version of the original YUM and uninstalling our current one, we can once again employ rpm but this time to re[–install] the package [–verbose]ly:

$ rpm --verbose --install yum-3.4.3-168.el7.centos.noarch.rpm
################################# [100%]
Updating / installing...
################################# [100%]

Alternatively, we can perform an –upgrade, although we’re pointing to the same version we had before:

$ rpm --verbose --upgrade yum-3.4.3-168.el7.centos.noarch.rpm

At this point, we should again be able to use yum:

$ which yum
$ yum --version
Installed: yum-3.4.3-168.el7.centos.noarch at 2023-06-06 06:56

Notably, we don’t need to handle any dependencies, despite performing an offline RPM installation. That might not have been the case had we not downloaded the same version of yum we already removed.

Critically, any custom directories, configuration changes, and similar would have to be applied anew.

3. Reinstall DNF Dandified YUM

In contrast to the original YUM, dnf is usually the default on more recent Linux distributions:

  • CentOS after and including version 8
  • Fedora after and including version 22
  • Oracle Linux after and including version 8
  • RedHat Linux after and including version 8

Importantly, the yum command still exists on such systems but only as a link to /usr/bin/dnf:

$ ls -l $(which yum)
lrwxrwxrwx. 1 root root 5 Sep 22  2022 /usr/bin/yum -> dnf-3

Moreover, the DNF package manager has several features:

  • well-documented API
  • very fast libsolv dependency resolution
  • much lower memory consumption
  • continues even after encountering unresponsive repositories
  • cleans up unnecessary packages that no other package depends on
  • allows any kernel package modifications

Despite these advantages, we might want to remove or reinstall dnf. Let’s see how.

3.1. Verify DNF YUM Installation

Again, we assume dnf YUM is already present:

$ dnf list installed dnf
Installed Packages
dnf.noarch                4.14.0-1.el9                @anaconda

In this case, the list option of dnf claims dnf version 4.14.0-1 is installed.

Further, since it’s at the base of RPM distributions, we can again employ rpm to –verify (-V) the installation:

$ DNFPATH=$(which dnf)
$ mv $DNFPATH .
$ rpm --verify dnf
missing     /usr/bin/dnf
$ mv dnf $DNFPATH
$ rpm --verify dnf

Apart from our forced one, there seem to be no issues in this environment. So, let’s get the installation RPM for our version.

3.2. Acquire DNF YUM Package

The dnf YUM package manager also has an RPM cache at /var/cache/dnf.

Since we probably won’t find the dnf package there, we turn to the original CentOS Stream 9 distribution repository at https://mirror.stream.centos.org/9-stream/BaseOS/x86_64/os/Packages/ :

$ curl --silent https://mirror.stream.centos.org/9-stream/BaseOS/x86_64/os/Packages/ | grep 'dnf-4.14.0-1'
[...]<a href=dnf-4.14.0-1.el9.noarch.rpm">dnf-4.14.0-1.el9.noarch.rpm</a>[...]
[...]<a href="python3-dnf-4.14.0-1.el9.noarch.rpm">python3-dnf-4.14.0-1.el9.noarch.rpm</a>[...]

In this case, we need the specific version of DNF YUM we had installed. Otherwise, we might need to download two other packages as well:

Let’s download dnf-4.14.0-1.el9.noarch.rpm, since that’s the exact version we removed:

$ curl --silent https://mirror.stream.centos.org/9-stream/BaseOS/x86_64/os/Packages/dnf-4.14.0-1.el9.noarch.rpm --remote-name

At this point, we have the DNF YUM package. Time to install it.

3.3. Uninstall DNF YUM

To remove dnf YUM, we use rpm with its –erase or -e option:

$ rpm --erase dnf
error: Failed dependencies:
        dnf = 4.14.0-1.el9 is needed by (installed) yum-4.14.0-1.el9.noarch
        dnf >= 4.11.0 is needed by (installed) yum-utils-4.3.0-7.el9.noarch

As expected, the dependency check fails, since both the yum and yum-utils packages rely on the dnf package.

Let’s confirm this with an rpm –query like before:

$ rpm --query --whatrequires dnf
$ rpm --query --whatrequires yum
no package requires yum
$ rpm --query --whatrequires yum-utils
no package requires yum

This time, we don’t have interdependencies. Thus, we directly –erase the dnf package with –nodeps:

$ which dnf
$ rpm --erase --nodeps dnf
Removed "/etc/systemd/system/timers.target.wants/dnf-makecache.timer".
$ which dnf
/usr/bin/which: no dnf in (/root/.local/bin:/root/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin)

In this output, we see side effects in the form of a cache-clearing timer removal. Of course, the dnf command is now gone.

3.4. Install or Reinstall DNF YUM

Like before, we leverage rpm to –install the dnf YUM package we just downloaded:

$ rpm --verbose --install dnf-4.14.0-1.el9.noarch.rpm
Verifying packages...
Preparing packages...
Created symlink /etc/systemd/system/timers.target.wants/dnf-makecache.timer → /usr/lib/systemd/system/dnf-makecache.timer.

Like with the original yum, we can perform an –upgrade to the same version:

$ rpm --verbose --upgrade dnf-4.14.0-1.el9.noarch.rpm

Finally, we have a working dnf command:

$ which dnf
$ dnf --version
  Installed: dnf-0:4.14.0-1.el9.noarch at Wed 06 Jun 2023 00:06:56 AM GMT

These short steps apply when we have the exact version of the dnf YUM package that we had previously. Changing a version requires more steps. and packages.

3.5. Change DNF YUM Version

Importantly, selecting a different version of the DNF YUM package from the one that was last installed might necessitate installing, removing, downloading, and reinstalling the respective dnf-data and python3-dnf packages:

$ rpm --erase --nodeps dnf-data
$ rpm --erase --nodeps dnf
$ rpm --erase --nodeps python3-dnf
$ curl --silent https://mirror.stream.centos.org/9-stream/BaseOS/x86_64/os/Packages/dnf-4.14.0-6.el9.noarch.rpm --remote-name
$ curl --silent https://mirror.stream.centos.org/9-stream/BaseOS/x86_64/os/Packages/python3-dnf-4.14.0-6.el9.noarch.rpm --remote-name
$ curl --silent https://mirror.stream.centos.org/9-stream/BaseOS/x86_64/os/Packages/dnf-data-4.14.0-6.el9.noarch.rpm --remote-name
$ rpm --install --verbose \
  dnf-data-4.14.0-6.el9.noarch.rpm \
  python3-dnf-4.14.0-6.el9.noarch.rpm \

This way, we can replace our installation with any version. Still, like with the original YUM, we need to reapply any custom changes manually.

4. YUM Debugging

In general, we might not want to reinstall YUM or DNF YUM as a whole. In such cases, we can try several steps that deal with the cache and metadata of the packaging system:

Remove packages from the cache:

$ yum clean packages

Remove metadata:

$ yum clean metadata

Remove database cache:

$ yum clean dbcache

General cleanup:

$ yum clean all

At this point, let’s try an update:

$ yum update

If the update fails, the RPM database at /var/lib/rpm might have been corrupted. In that case, as a last resort, we might try to rebuild the RPM database with –rebuilddb after deleting all db files from /var/lib/rpm:

$ rm --force /var/lib/rpm/*db.*
$ rpm --verbose --rebuilddb
$ yum update

In case the update fails again, a reinstall may be needed to resolve deeper issues.

5. Summary

In this article, we delved deep into the original and DNF YUM versions, as well as how to install, uninstall, and debug them.

In conclusion, although the original yum and dnf have many differences, their reinstallation process is fairly similar.

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