HOWTO: Repair a broken Ext4 Superblock in Ubuntu

This saved my behind today. Mkfs -n shows you your backup superblock locations. I was able to rebuild my root filesystem thanks to this! – View the original to see all the commands.

Linux Expresso

This has happened to me a few times, and it’s not a nice problem to find yourself in. You computer won’t boot, all your filesystem checks tell you you’ve a bad superblock, but you cant seem to find how to fix it. Well, here goes🙂

This guide is for ext4 , though I’ll explain how other filesystems can be cured along the way. The easiest way to carry all this out, seeing as your computer probably won’t boot at this stage, is to download and burn a copy of Parted Magic. Boot from that, and you’ll access to a number of useful tools.

First, figure out what partition we’re dealing with.

The above will list all the partitions on all the drives in your computer. To recover a lost partition, your going to need Testdisk. Testdisk is included in Parted Magic, and there’s a great guide on…

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Unrelated to flying and IT.. but I can’t not post about it.

For those of you that don’t know, I am also in a band. If any of you like Foofighters, Queens of the Stone Age, Biffy Clyro or any other modern rocky music you should like us.

Our name is Wolfetone

We have just finished recording an album and have put one of the tracks up here: Wolfetone – Tanks

More relevant posts coming soon! I have started contracting at a bank in the last month so there should be some more technical posts on their way. I’ve also been to the red bull air race here in the UK. Pics coming soon!

Thanks for taking the time to check us out!


Packet loss and TCP retransmits from a linux host?

These sorts of errors can be caused by almost anything.. but if you’ve exhausted most options perhaps it could be your TCP buffer size on your Linux host. This is often overlooked.

The below link shows you how to modify the default kernel parameters to allow higher throughput. This is usually only needed in exceptional circumstances where traffic flow is usually very large. (Again, don’t do this in production without testing it. I am not responsible for any changes you make to your systems.)

VMware VDP – Limit number of concurrent backups

We recently had a little issue with one of our vmware 5.5 clusters. – Backups started running and our lowly nexcenta iSCSI SAN appliance couldn’t handle the extra I/O.

By default, vDP (vSphere Data Protection) will run up to eight concurrent backups at a time, if you have 8 or more VM backups specified in the same job. There is no way to change this in the vmware web gui or vSphere client.
There is however, an unsupported workaround: 

  • SSH to your VDP appliance
  • cd /usr/local/avamarclient/etc/
  • ./

You will be presented with an interactive prompt. Hit return on the first prompt. You are then asked how many “proxies” you want to use. The default is 8 proxies. Choose a lower number to suit your requirements, such as 4 perhaps. Hit return and that’s it. No more than 4 backups will run at one time. Woop!

DISCLAIMER: This is not supported by vmware. You are editing the number of ‘proxies’ that vdp uses to run backup jobs. Apply these settings at your own risk.

Thanks to for this information. I can confirm it worked for me.

Configuring Bind DNS on Centos 6

Great guide here thanks to the guys at
I used this to get bind 9 up and running in our office, to replace tinydns that was implemented a while ago.

One thing this guide doesn’t mention is that your zone files in /var/lib/named MUST be readable by the ‘named’ user. If you copy an example file as root and try to use it, it won’t be in the right group, and the named daemon can’t read it. This will prevent named from answering any lookups.