reverse engineering things that predecessors left without any documentation and throwing them out the window because devops

Below python oneliner will show you YUM variables typically defined in /etc/yum.conf and used by YUM/RPM. Very cool.

The above YUM variables are further described at this Red Hat Knowledge Base article.

I have noticed the below error when one day i was starting up my KVM virtual machines to play around with Docker Swarm.

There wasn’t much information on google or forums and most talked about symlinks that weren’t there. Most folks recommended reinstalling seabios and seabios-bin. But unfortunately, reinstalling these packages did not provide the necessary files.

Upon further inspection of the package versions, I noticed that seabios-1.8.2-1.el7 does not provide /usr/share/seabios/bios-256k.bin. Now seabios-bin-1.7.5-11.el7 does provide that file.

Make sure that you are installing seabios-1.7.5-11.el7 and seabios-bin-1.7.5-11.el7. Check that you do not have /etc/yum.repos.d/CentOS-Xen.repo enabled. These packages should be pulled from


Sometimes on your RHEL-like system you may encounter the following error:

This may happen when you’re hosting your own YUM package repository and the group metadata in the repository is missing. This error is easily fixable on the YUM repo with createrepo command.

Log onto your repository server and go to your repo directory that contains “repodata” directory. Then run “createrepo -g”:

This will create the groups listing for your repository.

If you do not have the repodata/comps.xml file, try looking at the mirror that you’re mirroring from. It should have this file. Sometimes it may not be copied correctly, especially if you use reposync command to sync your repos.

Check the createrepo manpages for more goodness.

This one bugged me for a while. Whenever I would reboot my CentOS 7 server with Xen kernel, my console/framebuffer resolution would be terribly low. Since we live in 2016 and have huge monitors, there is no reason to use 800×600 for your screen resolution. Yes, it’s nice to keep your text editing to 79 columns, but these days we just do more than edit text in terminals (see tmux).

Anyway, to set a new console resolution in CentOS 7 with Xen kernel (on a dom0 of course), head over to /etc/default/grub.

If you are using Xen kernel, your grub config will will look like this:

Edit the file so it looks like this:

In this case we added the following lines:

Generate the new grub config file in /boot:

You should see something like this:

Now what we’ve done is remove the console handling stuff (I don’t use a serial console on my home hypervisor, but in a datacenter? Yes please!) and added the GRUB_GFXMODE and GRUB_GFXPAYLOAD settings. After rebooting the machine, you should see everything in a higher, crisper resolution on your monitor.

I’m writing this as a set of notes for future Arch Linux installations. I decided to revisit Arch Linux after hearing that their ncurses menu-based installer was long gone and how they have started using install scripts. I came upon this while reading the systemd vs SysV initialization method debate that everyone is raging about. I haven’t installed Arch in years as my current machines still happily run on the old installs which are up to date since Arch is a rolling release distribution. I figured now would be a good time to check it out (along with a growing interest in tiling window managers such as i3 or ratpoison).

Anyhoo, I installed Arch Linux from the latest ISO using the new method along with a help of numerous Arch wikis. I mixed the install a little bit with my way of setting up Linux computers and added LVM. One thing I must say is that installing Arch Linux has become a little bit harder than previous menu-based installation. I’m not saying it’s not doable, but it’s definitely a bit more complex or at least daunting for a newbie than just following some menus. It does help to know how Linux already works but this installation method should teach you a bit if you don’t know.
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Just a small, helpful tidbit:

If you ever see the following in your tcpdump while resolving SNMP issues (when isn’t SNMP having issues?):

It basically means that your iptables is blocking SNMP. This one has bit me on multiple occasions on boxes that were running iptables but should not have been. Either disable it or open up the port:

On RH-based distros:


Of course, don’t go disabling iptables, when you can simple open up the port :). I would also recommend using SNMPv3 whenever possible since it allows for encryption and authentications.



This is something I’ve noticed a few times lately on Red Hat Enterprise Linux 5 and I figured I’d post for future reference.

When mounting an nfs mount on a clean build of RHEL5, eg:

[code]sudo mount nfsserver:/home /nfsimports/nfsserver/home[/code]

You might notice that the client hangs. ¬†Running ‘tail -f /var/log/messages’ on the server reveals that the authentication completes, eg:

[code]Sep  9 13:55:31 nfsserver mountd[4549]: authenticated mount request from nfsclient:port for /home (/home)[/code]

If you see that, make sure to start portmap on the client, eg:

[code]sudo /etc/init.d/portmap start[/code]

Not starting portmap causes NFS mount to hang thus never completing its operation. ¬†Portmap is used for RPC calls and more information can be found here. This is a little gotcha that got me a few times while working with RHEL5. Most likely somebody will run into this problem as well as portmap isn’t set to run by default on base RHEL5 install.

Getting Acrobat Reader (or acroread) to work on the latest Ubuntu release was a royal PITA.  Previously it was installable through the Medibuntu repository, but unfortunately on Lucid it would come up with an error complaining of uninstallable libldap2 dependencies.

[bash]The following packages have unmet dependencies:
acroread: Depends: libldap2 but it is not installable
E: Broken packages[/bash]

Thankfully, I was able to install it by enabling the “partner” canonical repository in System > Software Sources.¬† Once then I was able to succesfully run:

[bash]sudo apt-get install acroread acroread-plugins[/bash]

Hopefully this small tidbit will help out those searching for some fixes on this issue as  I saw tons of posts on-line without an available fix.  I personally have found Acrobat much faster on Linux than on Windows and I could not stand some of the open source PDF viewers that came with Ubuntu (no offense to the programmers :)).  I like some of the extra features of Acrobat as well.