How to fix yum errors on CentOS, RHEL or Fedora

Yum is a package management tool for installing, updating and removing rpm packages on RedHat-based systems. When you try to install a package withyum command, you may encounter
errors for various reasons. In this post, I will describe under what situationsyum errors can occur, and explain
how to fix yum errors.

Fix 404 errors

Symptom: When you try to install a package with yum,yum complains that the URLs for repositories are not found, and throws 404 errors, as shown below.

Loaded plugins: fastestmirror
base                                                     | 3.7 kB     00:00
base/primary_db                                          | 4.4 MB     00:09
extras                                                   | 3.5 kB     00:00
http://mirror.steadfast.net/centos/6.4/extras/x86_64/repodata/e0e507c76dc5e5aa66c1f32632b9dc0a9759d97031ab5a028562a7cb7be6e294-primary.sqlite.bz2:
[Errno 14] PYCURL ERROR 22 - "The requested URL returned error: 404
Not Found"
Trying other mirror.
http://mirrors.seas.harvard.edu/centos/6.4/extras/x86_64/repodata/e0e507c76dc5e5aa66c1f32632b9dc0a9759d97031ab5a028562a7cb7be6e294-primary.sqlite.bz2:
[Errno 14] PYCURL ERROR 22 - "The requested URL returned error: 404
Not Found"
Trying other mirror.

You can get these 404 errors when the metadata downloaded by yum has become obsolete.

To repair yum 404 errors, clean yum metadata as follows.

$ sudo yum clean metadata

Or you can clear the whole yum cache:

$ sudo yum clean all

Fix connection failure errors

Symptom: You get "network is unreachable" or "couldn't connect to host" errors while runningyum command.

Loaded plugins: fastestmirror, presto
Loading mirror speeds from cached hostfile
Could not retrieve mirrorlist
http://mirrorlist.centos.org/?release=6&arch=x86_64&repo=os error was
14: PYCURL ERROR 7 - "Failed to connect to
2a02:2498:1:3d:5054:ff:fed3:e91a: Network is unreachable"
Error: Cannot find a valid baseurl for repo: base

http://mirror.nexcess.net/CentOS/6.4/os/x86_64/repodata/repomd.xml:
[Errno 14] PYCURL ERROR 7 - "couldn't connect to host"
Trying other mirror.
http://mirrordenver.fdcservers.net/centos/6.4/os/x86_64/repodata/repomd.xml:
[Errno 14] PYCURL ERROR 7 - "couldn't connect to host"
Trying other mirror.
http://mirrors.cmich.edu/centos/6.4/os/x86_64/repodata/repomd.xml:
[Errno 14] PYCURL ERROR 7 - "couldn't connect to host"
Trying other mirror.

The error means that you cannot properly connect to repository servers for some reason. If you can still ping the servers without any problem, check if your system is behind a proxy. If you are runningyum behind a proxy, but have not specified the
proxy in the yum configuration, you will get connection failure errors like the above.

To configure a proxy in the yum configuration:

$ sudo vi /etc/yum.conf

[main]
proxy=http://proxy.com:8000

Fix metadata checksum errors

Symptom: You get "Metadata file does not match checksum" while runningyum command.

epel/pkgtags                                             | 466 kB     00:14
http://mirror.steadfast.net/epel/6/x86_64/repodata/pkgtags.sqlite.gz: [Errno -1] Metadata file does not match checksum
Trying other mirror.

You can get the metadata checksum errors when the metadata downloaded by yum has become outdated.

To repair yum checksum errors, clean yum metadata:

$ sudo yum clean metadata

Fix yum lock errors

Symptom: When you run yum on Fedora, you get the errors saying that "Another app is currently holding the yum lock."

Loaded plugins: langpacks, presto, refresh-packagekit
Existing lock /var/run/yum.pid: another copy is running as pid 1880.
Another app is currently holding the yum lock; waiting for it to exit...
  The other application is: PackageKit
    Memory : 178 M RSS (586 MB VSZ)
    Started: Tue Jul  9 09:43:17 2013 - 00:12 ago
    State  : Sleeping, pid: 1880

The culprit for this error is PackageKit which is responsible for auto updates on Fedora. ThePackageKit process gets automatically started upon boot, holding the
yum lock.

To fix the error, disable auto update checks on Fedora. In order to do so, click on "Software" on Fedora desktop to open software update preferences.

Then click on "Software Sources" menu like the following.

In the software update preferences, set "Never" for "Check for updates".

Once you reboot your desktop, you will no longer get yum lock errors.