Mdadm Must Be Configured on Partition

Refer to my previous post Missing mdadm array after reboot, I would like to add on the reason why auto-scan does not work once system rebooted - it requires the RAID to be configured on a partition instead of the disks!

This is going to have problem:

mdadm --create --level=6 --raid-devices=5 /dev/md0 /dev/sd[b-f]

 and this would be correct, please take note of the digit at the end of line:

mdadm --create --level=6 --raid-devices=5 /dev/md0 /dev/sd[b-f]1

It means you must format all the disks with at least one partition, and building the RAID using the partition.

I  hope this would be helpful for novice users who trying to get the RAID run properly.

Problem Updating Repo List in Ubuntu 12.10

The sources list has been changed to old-releases. To replace the sources list easily, use the following command:

sudo sed -i -e 's/archive.ubuntu.com\|security.ubuntu.com/old-releases.ubuntu.com/g' /etc/apt/sources.list

If you have choose another mirror then your sources list might contain us.archive.ubuntu.com, then the above changes would still be invalid. You would need to remove the us. from it. Using the command below will help remove it:

sudo sed -i -e 's/us.old-releases.ubuntu.com/old-releases.ubuntu.com/g' /etc/apt/sources.list

Houdini Start-Up Crashed on Render Node

AFAIK, Houdini could not start its main application (GUI) without OpenGL enabled graphics card. Hence if you are trying to start it in a render node with ASPEED on-board graphics, it is impossible. All you can do is to run the render using CLI.

As for user encounters the same issue, if you are using Nvidia graphics card, you would need to switch the XORG graphics driver to Nvidia proprietary driver. You can do it at:

Menu > Settings > Software and Update > Additional Drivers

Sometimes the latest driver may not work well. So you may have to tried different version to get it work.

Tips: To get a clearer picture of why Houdini failed to start, instead of running it from software menu, you can run it from terminal. The error message will be more readable than the crashed dump file.

Missing mdadm array after reboot

It is heart-attack when you reboot your linux storage server and realized mdadm array gone missing!

• RAID volume not showing in gnome-disks.*
• gparted reports empty partition on all the RAID disks

sudo mdadm --examine --scan -v shows:

mdadm: looking for devices for /dev/md0
mdadm: Cannot assemble mbr metadata on /dev/sda
mdadm: Cannot assemble mbr metadata on /dev/sdb
mdadm: Cannot assemble mbr metadata on /dev/sdc
mdadm: Cannot assemble mbr metadata on /dev/sdd
mdadm: Cannot assemble mbr metadata on /dev/sde

sudo mdadm --examine /dev/sd*  or mdadm --query /dev/sd* shows:

mdadm: No md superblock detected on /dev/sd*

sudo mdadm --assemble /dev/sd[b-f] shows:

mdadm: device /dev/sdb exists but is not an md array.
mdadm: No arrays found in config file or automatically

If you go into /etc/mdadm/mdadm.conf (Debian / Ubuntu) or /etc/mdadm.conf (Fedora), you would realize there is no ARRAY being defined. In some system the mdadm.conf simply does not exist.

No matter how hard you try, the mdadm array just won't show up. There are numerous suggestion on the web, being the most common is to add an auto examine during boot in the mdadm.conf:

 sudo mdadm --examine --scan --config=mdadm.conf >> /etc/mdadm/mdadm.conf

However the above simply does not work for me. I have also try adding the ARRAY manually by doing the following, in which the UUID is the first hdd used for the array (to show the UUID, use blkid. Strange enough I could not get the UUID of my GPT hdd in Ubuntu, and only can get by using Fedora):

ARRAY /dev/md0 metadata=1.2 UUID="0db0c336:f56bd888:2f9e92e4:c1d64c09" >> /etc/mdadm/mdadm.conf

It does not work as well. I have no other solution except try to re-create the array again. Be very careful of this step, I'm more daring to take this step because I already backup my data one day before I lost the array. When you re-create the array, BE SURE to use --assume-clean and make sure the parameter set is EXACTLY the same as what you used to create it the first time. In my case, it is very simple and straightforward:

mdadm --create --assume-clean --level=6 --raid-devices=5 /dev/md0 /dev/sd[b-f]

The RAID array is being created and immediately I got all my data back!! It is advisable to backup your data now and once the backup is done, do a data scrubbing to ensure it is running well.

I hope you will be as lucky as I do, to have all the data back without losing great memory and important works.


External link that I used as reference:

• A very useful read: https://raid.wiki.kernel.org/index.php/RAID_Recovery
• https://hiringsolved.com/blog/goodbye-big-data-mdadm-no-recognizeable-superblock/
• http://ubuntuforums.org/archive/index.php/t-2090527.html
• http://kevin.deldycke.com/2007/03/how-to-recover-a-raid-array-after-having-zero-ized-superblocks/ (be very careful with this, I would not suggest zero out the superblock unless you know what it does)
• http://ubuntuforums.org/showthread.php?t=1950154
• http://superuser.com/questions/603481/how-do-i-reactivate-my-mdadm-raid5-array
• Changing UUID of a mdadm partition: https://itooktheredpill.irgendwo.org/2010/change-uuid-of-a-mdadm-partition/
• This is not useful in my case, but maybe helpful for others: http://askubuntu.com/questions/247981/software-raid-mdadm-re-find-my-array

* If it is shown, then you are lucky because it simply changes its name from /dev/md0 to something like /dev/md127. You can still use it by changing the mounting command to the new array name.

Never sign up VPS from this company

Recently I have sign up a VPS from a company call WideVPS, and it is really the worst hosting company that I have ever encounter. For those of you who like an affordable hosting, please be careful with the company:

1. The VPS is activated after a few hours of waiting. (they claimed it is instant activation)
2. Support ticket tooks 4 hours to response. (they claimed 1-hour response)
3. Ticket was closed even the issue has not been resolved. I created a Windows VPS for testing before moving to linux, during the sign up I have key-in a password for the VPS. When it is finally up after 4-hours, the password I entered is not working!! I then open a ticket and email, it tooks 2 days and never resolved! All I get is.... I will send you the info in next email. Then? I receive no email at all.
4. Submitted a PayPal dispute, but they never response to the dispute. (so you can see they are not serious in the business at all)

And this morning I receive their invoice asking me to renew the hosting, but until today I'm not able to use the VPS at all!

Guys and Gals, be careful. I'm glad if you have good experience with them. But if you are still considering, just make sure you contact them before sign up and then judge yourself. I hope you will then not wasting money like I did.

Ubuntu Boot to Blank Screen with Blinking Underscore (Cursor)

Today I was installing the Ubuntu 14.04.02 LTS into a server using a USB thumbdrive. Everything went smooth, as usual the setup asked to remove the USB thumbdrive before continue to Reboot.

After reboot, it hangs on a black screen with blinking underscore / cursor. Waited for 15 mins, nothing happen. If you encounter the same error like I do, it is possibly caused by:

1. a corrupted GRUB
2. the setup simply installed the GRUB onto the USB thumbdrive accidentally. (I suspect it is because I have chosen to umount the thumbdrive during the setup)
3. graphics driver not supported (it sounds a bit weird to me, if the setup could run well in GUI, why should a reboot not?)

For the first two reasons, a simple solution is to repair the GRUB. Here's the complete guide for Ubuntu users. For my case, because I knew the GRUB is in the thumbdrive, so I simply plug it in and choose my HDD as first boot device, it then boot into Ubuntu successfully, then I run the following command in terminal:

sudo add-apt-repository ppa:yannubuntu/boot-repair
sudo apt-get update
sudo apt-get install -y boot-repair && boot-repair

and then follow what is being instructed by the boot-repair. The only steps that caused a confusion is which disk or partition to select as GRUB install location. A rule of thumbs is don't select the partition, select the disk.

For 3rd reason - graphics driver broken. I personally do not try it, but someone from online said it can be fix by inserting the -nomodeset in between ro quiet splash. And I do believe you realize one thing now... if you could see the GRUB and able to insert the -nomodeset, well, then it is most likely your problem is more challenging, good luck hunting it down!

XFCE4 Desktop Not Showing

Sometimes when you login the desktop wallpaper, icons are all missing. It is due to the xfdesktop not loaded properly. To fix it, simple type xfdesktop in terminal, there will have some message appeared but can be safely ignore.

[Fedora] Fix Yum Update crashed at the middle of updat

If the problem you having is duplicates packages, simply refer to the following info to attempt the fix:

sudo yum check all                # tells you of any problems
sudo package-cleanup --problems   # lists all known package problems
sudo package-cleanup --dupes      # lists duplicate packages
sudo package-cleanup --cleandupes # actually cleans up duplicates
sudo yum check all                # run again to check for remaining problems
sudo yum-complete-transaction --cleanup-only

Thanks to https://destefano.wordpress.com/2013/08/13/yum-update-fail/#comment-2714