Posts Tagged ‘ubuntu’

Boot Ubuntu from RAID

May 13th, 2016 No comments

I had lately setup RAID 5 (three 2TB disks) with i7 6700 + ASUS H170 MoBo + 32GB DDR4 RAM followed by installing Ubuntu 16.04 x64 on it.  The installation went very well with Kernel 4.4.0-21.  But, upon restart the installation was unable to move ahead as the Kernel was not able to read from the RAID device.

Basically, the issue is that the install kernel didn’t have the RAID drivers embedded within.  Upon digging for few hours, found one solution at , which didn’t work as is.  The following modification worked:

  1. Boot from Live DVD image, which would load the RAID drivers automatically allowing you to see the device correctly.
  2. Now mount the root partition. (say /mnt/root-partition)
  3. Edit /mnt/root-partition/etc/initramfs-tools/modules for adding drivers that should get embedded into Initialization RAM drive file System (initrd).
  4. Add the following list at the end of the modules file.  The list is generated using “lsmod|grep raid” during the live DVD session.
    1. dm_raid
  5. Run “mkinitramfs -r /mnt/root-partition -o /mnt/root-partition/boot/initrd.img-4.4.0-21-generic”
  6. Reboot the machine to see that RAID is being detected.
  7. Install dmraid (apt-get install dmraid), which would again fix the initrd image with necessary stuff.
  8. Now, my machine works smooth.

If nothing worked, get a small HDD to install the OS in it.  While booting the OS, you may load the drivers via /etc/rc.local and dmraid commands to activate the RAID device and mount it for use.

Installing nvidia driver in MSI GE72 6QD

February 11th, 2016 No comments
  1. Uninstall all nvidia drivers.
    GRUB_CMDLINE_LINUX_DEFAULT="quiet splash i915.preliminary_hw_support=1 i915.enable_execlists=0 intel_pstate=disable i915.enable_rc6=0"
  3. Then run sudo update-grub2 to make the change permanent.
  4. Restart your laptop to witness the proper function of video screen, which is using the Intel GPU now.
  5. Now you can change the screen brightness using the Fn+Brightness key. Previous to this change, my screen brightness remained the same always.
  6. Install the latest nvidia driver using apt-get. In my case, I installed 361.18 and my Kernel was 4.2.0-27
  7. Restart now and see nvidia driver in action. I had checked the functionality by running nvidia-settings.


Update:  In 16.04 Xenial release, I get a lot of the following errors

PCIe Bus Error: severity=Corrected type=PhysicalLayer, id=00e0(Receiver ID)
device [8086:a110] error status/mask=0000001/00002000
[ 0] Receiver Error

This problem can be overcome by adding pci=noaer to GRUB_CMDLINE_LINUX_DEFAULT.

Automated Linux GUI Applications using X11::GuiTest

November 3rd, 2015 No comments

Lately, I wanted to extract from application-embedded medical lexicon to construct a database for easy use of the lexicon data.  The application was ancient (1998) and Windows 32bit.  The application does not work in Windows version beyond Windows XP 32bit.  But fortunately, the application was very runnable in Ubuntu 14.04 over Wine layer.  A snapshot of the application is shown below:


There were several restrictions in the application, viz.,  “Select All” does not work, direct copy-paste does not work.  But the traversal of lookup items on the left pane could be fully done using keyboard keys.  So, the process for extracting every item is:

  1. TAB + TAB to go to the left pane containing the lookup items
  2. TAB to move to the right pane.
  3. Ctrl + Shift + End would select the entire text on the right pane.
  4. Ctrl + C copies the selected text to the clipboard
  5. Using “xclip”, it is possible to get the clipboard data into the driver script.
  6. Save the recovered clipboard content to a file.
  7. Move back to the left pane by Shift + TAB.
  8. Down arrow to move to the next item in the list.
  9. Goto Step 2, until exhaustion.

The ideal toolkit for this project is the X11::GuiTest library in Perl ( The same toolkit is available in software repository, which could be installed using sudo apt-get install libx11-guitest-perl.  The codeblock that I’d used in Perl for getting is done is listed below.

# Start the application 

# wait unconditionally for 5 seconds to allow the app to come to front.

# move the cursor to the scroll list
SendKeys('{TAB 2}');

for (my $i = 0; $i < 20; $i++ )
 # move the cursor to the right pane

 # select all

 # perform copy
 # read the data from clipboard and print that in stdout
 my $clipboard = `xclip -selection clipboard -o`;

 if ( $clipboard ne $clipboard_prev ) { print '-'x 80; print "\n$i\t$clipboard\n" };
 $clipboard_prev = $clipboard;
 # move back to scroll list

 # goto next item in the list.


Recovering KNotes Data

October 5th, 2015 No comments

The HTML data of KNotes app is stored at


The data can be copy-pasted across to recover from the previous installation.

RAID Mayhem in Linux Mint 17.1 and Kubuntu 14

March 11th, 2015 No comments

I have a Quad-core machine that has 2+2 1TB disks configured in RAID 1+0 mode (mirror + stripe).  I am having a 64Gb SSD, on which I have the operating systems installed.  Recently, I wanted to install Linux Mint 17.1 on the SSD.  The installation went fine, but after rebooting the RAID device was not visible at all.  To overcome this problem, I had to do “dmraid -ay” to activate the RAID device in my machine.

Ok, now my RAID device is visible.  Went ahead to create /home and /data partitions, followed by updating the same in /etc/fstab for auto-mounting during boot-up.

To my surprise, the reboot failed saying /home is not ready.  Checked into recovery mode by punching in the root password and found that the RAID device has gone missing now.   Ran “dmraid -ay” again to activate the device; following by running “mount -a” make /home and /data partitions come alive.  Exited the recovery mode to complete the full booting.

Did some internet search for how to activate the RAID device on booting automatically.  It was awful that there are no direct methods to do so.   Infact, some people have advised about not rebooting the machine at all..  Funny!

Later, found a workaround, where the /etc/fstab entries were made “noauto”.  And RAID activation happening in /etc/rc.local.


dmraid -ay
mount /home
mount /data


/dev/mapper/pdc_cjcdcdeide6    /home ext4    defaults,noauto     0   2
/dev/mapper/pdc_cjcdcdeide5    /data ext4    defaults,noauto     0   2

Moral: Never install the Operating System on a RAID device, as majority of the distributions don’t recognize them by default.  Interestingly, Fedora 21 recognized RAID during installation itself, but I ended up hating it, when I found “yum update” not working out of the box.

How to make Kate remember last opened files

October 22nd, 2014 No comments

Kate allows document editing to be grouped under separate sessions.  Although there is no direct configuration setting to make Kate auto-open last opened files during startup, the Sessions features come handy.  The workaround is; given that Kate remembers last opened file paths in the File -> Open Recent menu item, you may select files one by one to continue editing.  But, this is so boring.

The procedure is the following:

  1. Open all the files that you want to be remembered by Kate for reopening during next restart of Kate.
  2. Click on Sessions->Save Session As->[give a session name here to save the session]
  3. Close your Kate application.
  4. Open it again, you would see no files reopened automatically, Don’t Panic!
  5. Click on Sessions->Quick Open Session->[session name].
  6. Aha… all the files that you had put into the session will reappear.

Hash Overflow due to 64 bit upcasting

October 28th, 2011 No comments
    Lately, I had to debug the following piece of code, where it caused overflow on the hash bucket design.  The code worked perfectly on a Windows machine while compiled for Win32, but failed to work on a Linux Mint x64 machine.  The code is listed below, which basically calculates hash value of an input 32 bit unsigned number, limiting the hash value to 2^10 (1Meg).

hash = ( fpArray*2654404609 )>>12; // Calculate the hash and limit the value to 2^20 (1 Meg)

   When the input value for fpArray was 1724463449 (0x66C93959), the hash value generated was 1779068547 (0x6A0A6E83), which is more than (0x000FFFFF) to cause the hash bucket overflow.

unsigned hash = fpArray * 2654404609;
hash = hash >> 12;

    When I rewrote the code like the above, the value of hash was 2800236889 (0xA6E83959).  Upon shifting right by 12 yields 638651 (0x0009BEBB), which is the correct and expected hash value.

    Overall, the first snippet of code appears to be correct.  Do you see a problem there?  I couldn’t find the issue, until I recalled the 32bit vs 64bit difference.  If you carefully look at the multiplier 2654404609 (0x9E370001), although appears to be a valid 32 bit number, what is the default assignment of type to this number by the compiler?  If it was assigned 64bits, what would happen to the results?  To validate this, I changed the 2nd snippet as the following.

unsigned long hash = (unsigned long)fpArray * 2654404609;
hash = hash >> 12;
unsigned h2 = (unsigned)hash;

    Now, when the input is the same 1724463449 (0x66C93959), the value of hash becomes 4577423727077636441 (0x3F8646A0A6E83959) and upon right shifting by 12 bits yields 1117535089618563 (0x0003F8646A0A6E83). Followed by downcasting to unsigned yield 1779068547 (0x6A0A6E83). Bingo!

    So, what is happening here? While performing (fpArray * 2654404609), the computation is upcasted to 64bit computation by the 64 bit compiler.  So, what is the solution? Just put a “U” at the end of the constant.

hash = ( fpArray*2654404609U )>>12; // Calculate the hash and limit the value to 2^20 (1 Meg)
const unsigned multipler = 2654404609; // here U suffix is not needed as the constant is explicitly made unsigned
hash = ( fpArray * multiplier ) >> 12;

    Now, the computation will happen with 32 bit numbers to get the expected outputs.

Lessons Learned here:

  1. While using constants, beware of the upcasting and downcasting. So use proper suffixes like U, L, F etc.
  2. Instead of using constants directly in expressions, use them as constant variables.
  3. Be conscious about the compiler type and the assumptions made by the compiler in different build modes.

kDevelop Editing Freezes Problem

August 20th, 2011 No comments
While working with KDevelop 4.2, I was quite disturbed by suddenly freezing of editing window. In the sense, the opening file is uneditable, “find” strings does not work and literally kDevelop becomes unusable. I had to restart kDevelop 4.2 to resume editing the code. I believed that kDevelop is going into Vi mode and was trying to undo that. But that’s not the problem.

When kDevelop loses focus, somehow the editing capability is disabled temporarily. When you switch context a couple of time by Alt-Tab and land is kDevelop again, the editing capability is resumed. I don’t know whether this is a bug, but context-switching has been my breather for now.

PROXIM ORINOCO 802.11 a/b/g/n

June 30th, 2011 No comments

Did you try this page for the driver?

Procedure for setting up proxim driver is given here:-

If you want to try an alternate device, use this list linux compatible devices:-

How to on Wireless networking:-

If there is a windows driver, you can use “ndiswrapper” to setup a Linux module atop the windows driver sys and inf files. Try this as well.