Tag: yum

Running VMs? Delete wireless packages!

A best practice for system configuration is to remove any unneeded software. It’s sometimes difficult to know exactly what is needed and what isn’t, but CentOS 7 minimal and CentOS 8 minimal both install a number of packages related to wireless networking. If you’re running a server or a VM there’s almost never a need for these to be present.

To identify packages, I used yum search (substitute dnf for yum on CentOS 8):

yum search wireless

I used the same command a redirected the output to a file:

yum search wireless >wireless_packages

To get just the package names and convert it to a space-separated list, I used grep, cut, and paste:

grep -v Summary wireless_packages | cut -d. -f1 | paste -d' ' -s

You can remove them with the following command:

sudo yum remove iw iwl6000-firmware crda iwl100-firmware iwl1000-firmware iwl3945-firmware iwl4965-firmware iwl5000-firmware iwl5150-firmware iwl105-firmware iwl135-firmware iwl3160-firmware iwl6000g2a-firmware iwl6000g2b-firmware iwl6050-firmware iwl2000-firmware iwl2030-firmware iwl7260-firmware

iw and crda were not installed, so were ignored. The rest were removed.

This may seem trivial, but it frees up some disk space (~100MB) and it means that these packages won’t need to be updated in the future. Getting notifications from your monitoring systems or vulnerability management systems about updates or security updates to unused and unnecessary packages should be avoided.

yum Error: requested datatype primary not available

I ran into a new-to-me yum error earlier today:

$ yum --quiet check-updates
Error: requested datatype primary not available

Following the tips on Unix & Linux StackExchange: Error: requested datatype primary not available, I:

  • ran yum clean all
  • disabled repositories one at a time to identify the repo that was causing the error

In my case, it turned out to be the extras repo. The following did not produce any errors:

$ yum --quiet --disablerepo=extras check-updates

What is wrong with the extras repo? It is defined in /etc/yum.repos.d/CentOS-Base.repo, so I took a look at what was there:

[extras]
name=CentOS-$releasever - Extras
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=extras&infra=$infra
#baseurl=http://mirror.centos.org/centos/$releasever/extras/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7

None of that looked unusual (or had changed recently), so back to Google.

I tried excluding the specific mirror that was listed for the extras repo (http://mirrors.unifiedlayer.com/centos/7.4.1708/extras/x86_64/) by adding unifiedlayer.com to the exclude line in /etc/yum/pluginconf.d/fastestmirror.conf, as described in yum and fastestmirror plugin. Although yum appeared to pick a different mirror it still gave me the same error.

It turns out, the mirror in question was “poisoned” (rerouted) by my DNS servers, as it had been identified (possibly erroneously) as malicious. As such, the domain still resolved but the path to the CentOS repository did not exist.

I didn’t think that excluding the domain in fastestmirror.conf was having the intended effect, and yum was still trying to contact the bad mirror. I took the following steps, which resolved the error, although I can’t say I entirely understand why:

$ sudo yum makecache

This still produced the error.

I removed the bad entry from:

/var/cache/yum/x86_64/7/extras/mirrorlist.txt

Then I ran makecache again:

$ sudo yum makecache

No error this time! I tried running check-update:

$ yum check-update

No error!

Shouldn’t yum clean all have eliminated the bad cache value in /var/cache/yum/x86_64/7/extras/mirrorlist.txt?

Cache invalidation, one of the hard problems. At least I have steps to take if I run into this problem again.