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.

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

How to extend screen to second monitor in Linux / Fedora?

Here's the command that could extend the screen to second monitor, in case Linux does not do the job automatically:

xrandr --output VGA1 --mode 1920x1080 --output eDP1 --mode 1366x768 --left-of VGA1

Where you need to replace the screen size manually. By running xrandr in terminal, you could get the screen size range for each display output.

Beside --left-of, there are other options such as --above, --below, --right-of

[Alt] key problem when remote desktop Windows via Remmina

If you are using Xfce 4 and encounter the following problems using [Alt] key inside Microsoft Windows remote desktop session:

• [Alt] key does not work as per expected
• clicking [Alt] + mouse middle button move you away from your remote desktop session

then you should try this simple and straight forward trick before going too technical.

• Go Settings > Settings Manager > Window Manager Tweaks > Accessibility > "Key used to grab and move windows" > set it to "None"

Voila! Now it should works like charm. Otherwise... you might have to Google around and read about re-map key, etc.. Good luck!

Remmina - Unable to connect RDP Server

Have you ever encountered sudden failure to RDP to your Windows desktop using Remmina? There are two known reasons to me:

1. your RDP plugin for Reminna is missing. In Fedora, type sudo yum install remmina-plugins-rdp, or Ubuntu sudo apt-get install remmina-plugin-rdp. You may require to reboot after install in order to load the RDP plugin. Sometimes Import simply won't work.
2. your remote desktop's fingerprint has changed. It is impossible to reset the fingerprint within Remmina's interface. What you can do is fire up terminal, go to ~/.freerdp/ and delete known_hosts.

Now try again and voila! Your remote desktop is back!

[Fedora] Omit GUI and boot with or into command line

Before you start, you need to know what is runlevel.

runlevel is a number that indicates which mode the computer to boot into. For instance, runlevel 5 is graphical mode, where runlevel 3 is text-only mode. Runlevel 1 is single-user mode, commonly used for troubleshooting.

And GRUB (GRand Unified Bootloader), a bootloader which allow you to choose which OS to boot into during computer start up. Here's a screenshot of GRUB.

Now, there are two options:

1. boot with command line, means omit the filling up Fedora logo and show the boot progress by command line
2. boot into command line, means completely omit booting into GUI and end up in command line

What you need to do is at the GRUB screen, select your Fedora OS name and press "e".
Then find rhgb in the line start with linuxefi /vmlinuz. On the right side of rhgb should be word "quiet".

For option 1: Remove the rhgb from the line and press CTRL+X or F10. This should show the command lines as boot progress instead of the Fedora logo. Useful for identifying what has failed during boot progress. The system will still end up in GUI afterwards.

Sample = ... rhgb quiet ... 

For option 2: Here's why you have to understand the runlevel. You achieve this by simply add a runlevel number "3" after the word "quiet" (space in between two words) and press CTRL+X or F10. This should boot the system into CLI instead of GUI.

 Sample = ... rhgb quiet 3 ...

Note:

• rhgb = RedHat Graphical Boot

How to solve chmod doesn't work on mounted folder

When chmod does not have any effect on mounted folder, it could be wrong filesystem flag being used:

• try umount the folder first
• if you mount folder is a HDD, check its filesystem type by fdisk -l
• if it is a NTFS, use the following in fstab :
•  /dev/sda1    /mnt/folder    ntfs-3g    rwx,uid=xe4,iocharset=utf8,umask=000    0    0
•  then mount -a

Then the chmod should work now.

[Fedora] Laptop Broadcom Wireless not working?

The downside of Fedora compared to Ubuntu on my laptop is the Broadcom BCM4312 wireless device doesn't install automatically, that mean I'm unable to turn on my wireless for net browsing.

Luckily, how-to instruction is well documented in FedoraForum.org:
http://forums.fedoraforum.org/showthread.php?t=239922

How to Fix Multi-boot, Fedora Gone after Install Ubuntu

Updated 30 Jan 2013 11.25pm:
A much more user-friendly method with GUI. Click here to see how.

---

I was installing multi boot environment on my laptop, it will be consist of:

1. Windows 7 Pro
2. Fedora 18
3. Ubuntu 12.10

Fedora & Ubuntu both use Grub2 to multi boot, installing Fedora after Windows work fine, but once Ubuntu was installed only Windows 7 can be seen from the list, Fedora was gone. How do we fix that inside Ubuntu?

There are various fix on internet which can be concluded below:

1. update-grub: you might have to install grub first before you able to run this command
2. grub-customizer: this is very handy GUI to manipulate the Grub. It supports Grub2 and it is real intuitive to add new OS onto the Grub menu list.
3. manual configuration by typing entries: intermediate/advanced user might appreciate this but definitely not for novice user. There are too many things to learn before one can eventually get it run correctly.

The first two methods are the most straightforward method, but it might not work as expected sometimes. My version of getting this solve is pretty simple, despite it required to work with method no. 3.

* To edit grub.conf user is required to open Nautilus with sudo privilege. Make sure you have run sudo nautilus & in terminal to be able to open and edit the configuration file in text editor.

1. First thing you have to know where the Grub configuration file is stored. It is located under /boot/grub/grub.conf. Open it with a text editor.
2. Then you have to know where is your Fedora /boot located. We don't need terminal as we love GUI. Go to Dash Home > Disks.
3. If you follow Fedora installation guide you can easily identify the /boot, which is 25x MB in size. There are two in my Disks Manager, but the already mounted one is for Ubuntu. So the other one is Fedora for sure.
   
   
4. Mount the Fedora /boot by select the partition and press the play button. 
5. Open the /boot/grub2/grub.conf with text editor.
6.  Locate the following and COPY the whole content except for the ###BEGIN....### & ### END....###:

7.  ### BEGIN /etc/grub.d/10_linux ###  
    menuentry 'Fedora' --class fedora --class gnu-linux --class gnu --class os
   . 
   .
   . *this dots mean there are a lot of content in the middle but being skipped
   . for ease of reading purpose
         }  
    }  
    ### END /etc/grub.d/10_linux ###  

8. After that, switch to your Ubuntu's grub.conf, and paste into ### BEGIN /etc/grub.d/40_custom ###, see screenshot below:
   
   
9. Save the Ubuntu's grub.conf and reboot.

Voila! My Fedora 18 is now shown on the Grub boot menu.

[Fedora 17] How to disable xscreensaver?

Under LXDE, I have disabled screen saver in KDE System Settings, but why I couldn't get rid of the "xscreensaver"?

It  is because the xscreensaver is not control by the setting in KDE system, but it is control by going to Application Menu > Preference > Screensaver.

Choose Disable Screensaver from the drop down menu. Bingo!

[Fedora] Mounting a network shared folder under LXDE X11 Desktop

Switching from Xfce to LXDE has made me unable to access my network shared folder. The reason is using Nautilus in Xfce will automatically mount the network folder. But in LXDE, the network folder is not mounted by default, and I need to mount it using command line.

The bad thing is as a novice user, command line doesn't work as smooth. Luckily there is a tools namely "Gigolo" to simplify the procedure. It is located under Application Menu > System Tools > Gigolo. In some case it does not come with LXDE installation, then one would need to manually install it, yum install gigolo.x86_64.

Open up Gigolo we can see a connect button, press it and set the following:

• Service type = Windows Share
• Server = your server hostname / IP address
• Share = the shared folder you would like to mount
• Domain = this can be left blank
• Username = username to access the server

Once enter / connect is pressed, there could be a pop up dialog (single line field) asking for password. For some reason entering password doesn't get rid of this dialog. Simply close it, then there will be another dialog box pop up, this time with two text field - Domain & Password. Simply ignore the Domain field and key in password. Voila! The network folder is now mounted.

[Fedora] How to disable C6 Media Repo

There are two methods being discussed online:

• yum --disablerepo=c6-media
• yum-config-manager --disable c6-media (this one work for me)