leemes's questions

On a fresh Lubuntu 13.04 installation, I installed Qt5 from the official ubuntu repositories. But this installation of Qt5 can't find the QtQuick module. What am I missing?

qmlscene test.qml

test.qml:

import QtQuick 2.0

Rectangle {
}

Output:

file:///home/.../test.qml:1 module "QtQuick" is not installed

I already double-checked that the following relevant packages are installed:

$ dpkg --get-selections | grep libqt5
libqt53d5:amd64                 install
libqt5clucene5:amd64                install
libqt5concurrent5:amd64             install
libqt5core5:amd64               install
libqt5dbus5:amd64               install
libqt5declarative5:amd64            install
libqt5designer5:amd64               install
libqt5designercomponents5:amd64         install
libqt5gui5:amd64                install
libqt5help5:amd64               install
libqt5location5:amd64               install
libqt5network5:amd64                install
libqt5opengl5:amd64             install
libqt5opengl5-dev               install
libqt5printsupport5:amd64           install
libqt5qml5:amd64                install
libqt5quick5:amd64              install
libqt5quickparticles5:amd64         install
libqt5quicktest5:amd64              install
libqt5script5:amd64             install
libqt5sensors5:amd64                install
libqt5sql5:amd64                install
libqt5sql5-mysql:amd64              install
libqt5sql5-sqlite:amd64             install
libqt5svg5:amd64                install
libqt5test5:amd64               install
libqt5v8-5:amd64                install
libqt5webkit5:amd64             install
libqt5widgets5:amd64                install
libqt5xml5:amd64                install

I'm using 11.04 (I know that support has been dropped) 32bit on my Desktop machine.

I never had performance problems with Adobe Flash on Ubuntu. But since today, all flash videos in browsers are insanely jerky so that I can't enjoy watching them. CPU usage is at about 20%.

I really don't know what happened. The only thing changed since it worked last time was that I plugged my TV as a second monitor on my graphics card and mirrored the screen. I have an Nvidia GTX 560Ti and use the driver version 173.

I tried both Firefox and Chromium, with both flashplayer-installer and adobe-flashplugin - none of them worked. https://www.adobe.com/software/flash/about/ tells me that I have flash version 11.2.202.243. It's strange that they say that 11.2.202.251 should be available, but I think this is an update issue of my outdated Ubuntu version (11.04).

If I could at least find out what the bottleneck is... CPU usage is very low as already said, it also isn't a buffering issue (HTML5 plays very well by the way). I don't know how to get the GPU usage, however, the Nvidia GUI reports no increasing temperature.

Do you have any idea what is causing this issue?

I have (had?) a RAID5 with 3 devices. One of them died, and after some days I experienced that the RAID stopped at all. However, I could restart it without experiencing any problems, but it stopped again after a few hours, I restarted it and it stopped again after some moments and so on. Since one month, the RAID can't start anymore. (Within the last month, I didn't do anything with the RAID as I hadn't time for it.)

I don't know if this is a hardware failure (of the drives) or "just" a defective contact of the power cable, since I had problems with this one year ago. I'm currently hoping for "just" a defective contact. The RAID holds mainly data of which I have a backup, however, the backup doesn't hold changes made within a month or so.

I found this blog post about recovering from a RAID5 with two failed disks. It describes a similar problem that I (hope to) have: The drives (or, at least one of the two failed ones) isn't really defective but only has been detached from the computer. Their approach is to re-create a RAID5 using all but the first failed device.

In my case, I have three disks, one of them is dead. So I have only two left: /dev/sda1 and /dev/sdc1, while the latter is the one which has been "detached" (at least, I hope it is not dead). So I hope to get the most important information from examining this device:

sudo mdadm --examine /dev/sdc1

          Magic : a92b4efc
        Version : 0.90.00
           UUID : 83cb326b:8da61825:203b04db:473acb55 (local to host sebastian)
  Creation Time : Wed Jul 28 03:52:54 2010
     Raid Level : raid5
  Used Dev Size : 732571904 (698.64 GiB 750.15 GB)
     Array Size : 1465143808 (1397.27 GiB 1500.31 GB)
   Raid Devices : 3
  Total Devices : 2
Preferred Minor : 127

    Update Time : Tue Oct 23 19:19:10 2012
          State : clean
Internal Bitmap : present
 Active Devices : 2
Working Devices : 2
 Failed Devices : 1
  Spare Devices : 0
       Checksum : eaa3f133 - correct
         Events : 523908

         Layout : left-symmetric
     Chunk Size : 64K

      Number   Major   Minor   RaidDevice State
this     1       8       33        1      active sync   /dev/sdc1

   0     0       8        1        0      active sync   /dev/sda1
   1     1       8       33        1      active sync   /dev/sdc1
   2     2       0        0        2      faulty removed

So it was October 23rd when the RAID stopped working at all.

Now I want to recover using the two devices with the command

sudo mdadm --verbose --create /dev/md127 --chunk=64 --level=5 --raid-devices=3 /dev/sda1 /dev/sdc1 missing

I hope someone can tell me if this is the correct command to use. I'm very nervous... It is telling me to confirm the following data about the drives to use to re-create the array:

mdadm: layout defaults to left-symmetric
mdadm: layout defaults to left-symmetric
mdadm: layout defaults to left-symmetric
mdadm: /dev/sda1 appears to contain an ext2fs file system
    size=1465143808K  mtime=Tue Oct 23 14:39:49 2012
mdadm: /dev/sda1 appears to be part of a raid array:
    level=raid5 devices=3 ctime=Wed Jul 28 03:52:54 2010
mdadm: layout defaults to left-symmetric
mdadm: /dev/sdc1 appears to be part of a raid array:
    level=raid5 devices=3 ctime=Wed Jul 28 03:52:54 2010
mdadm: size set to 732570816K
Continue creating array? 

Additional info: I once created the array with 3 * 750GB drives, so the file system is 1.5TB (ext2). In particular, I wonder if the line telling that /dev/sda1 contains a 1.5TB ext2 file system is correct, because in the blog post linked above, their output doesn't show such a line...

I also wonder if I should zero the superblock on any device first...

Are there any checks I can do to confirm that this will most probably not kill something totally for which there exists a chance to recover from?

I have an Intel GMA 950 chipset in my netbook. I want to learn how to write OpenGL shader programs with this fantastic tutorial and therefore need OpenGL 3.3. Sadly, my graphics card only supports OpenGL 1.4.

I think that MESA can emulate OpenGL in software, so I'm wondering if it can emulate OpenGL 3.3 without any hardware accelleration (performance is not a problem, since this is only for learning and testing puroses, even excluding profiling).

Is there any possibility to do this?

I want to configure a dial up network connection via bluetooth to my phone in order to access the internet.

I use Lubuntu 12.04 (Ubuntu with LXDE) which has the Network Manager Applet and Blueman applet installed. I guess these are the same tools than on an Ubuntu installation, hence I ask my question on this site.

My phone is a Sony Ericsson W810i, my laptop is a Lenovo S10-2, my mobile phone provider is o2 Germany.

I scanned for my mobile phone using the Blueman applet. I connected the dial-up network via the context menu -> Serial Ports -> Dial-up Networking. A notification bubble says that the connection is available on the interface named ppp0.

ipconfig is telling something different: There is no ppp0 or something similar. I only see my eth0 (wired ethernet), eth1 (wifi) and lo interfaces. Of course, I can't ping google.com as the interface really seems to be not present at all.

When the dial-up network is being connected, my mobile phone says that it connects to the internet. Afterwards, I see the active connection on the phone's screen. When successfully connecting with the phone using another computer, it behaves exactly the same, so I guess that the phone isn't the problem.

I don't know if I configured the Dial-Up correctly. I use the phone number *99# which is very common on most mobile ISPs. I use the APN which my ISP is telling me to use. (I can't find the number on their support page, so I just use the default value *99#.) My mobile ISP is o2 Germany.

There are How-Tos out there which use the Network Manager Applet to setup a bluetooth dial-up connection, but I can't see any bluetooth devices in the context menu as on the screenshots in those How-Tos.

Do you have any suggestions what might be wrong / what I should try?

EDIT:

When choosing "Network Access Point" in the device's context menu instead of Serial Ports -> Dial-Up Networking, an interface bnep0 appears. However, neither an IPv4 address is assigned for that interface (but IPv6), nor the phone connects to the internet. Am I missing something? Can I connect to the internet after setting up this network connection?

I want to create an alias for cd - which should be just a dash (-). I tried without success:

alias -='cd -'     # bash: alias: -=: Invalid option
alias \-='cd -'    # bash: alias: -=: Invalid option
alias '-'='cd -'   # bash: alias: -=: Invalid option
alias '\-'='cd -'  # bash: alias: `\-': Invalid alias name.

The former three are the same (only different input, but bash turns all of them into the same command alias with a single argument -=cd -), so it's no surprise the error message is the same. I'd guess that if the argument starts with a dash, it's parsed as a flag rather than the alias name.

Is it even possible to use - as an alias name?

I have a home server sometimes running at a high CPU usage rate of about 50 to 70 percents.

In htop, my favorite process manager, I can sort the processes by CPU usage, but often there isn't any process consuming more than 0 % CPU. On the other side, htop displays the whole CPU usage of the system which is about 50 percents, as said before.

I guess that there is an easy explanation for this, but I don't know it.

Maybe there are some hidden processes? But even running it as root doesn't show more processes.

EDIT:

I looked into top, which is showing (at least) two more processes:

  230 root      20   0     0    0    0 R 37.4  0.0 107:06.59 md127_raid5                                          
20403 root      35  15     0    0    0 D  9.6  0.0   2:45.78 md127_resync   

So my mdadm raid is currently resyncing, which has been confirmed when I displayed /proc/mdstat. (See first comment.)

So this turns the question in: "Why doesn't htop display the same processes than top?"

I was looking into htop and the only process having > 0.0% CPU (apart from htop itself) was /usr/lib/udisks/udisks-daemon.

So the questions are: What is this service? Do I need it? (Or when do I need it?) Why is it accessing the drives?

I have installed ubuntu 12.04 on my Thinkpad Edge (UEFI) using an USB-Stick. I guess it has been botted using EFI since a GRUB menu appeared with the options to boot a live system, install, or check the disk.

When I boot my laptop, grub only shows its command line prompt "grub>".

After manually running grub-install /dev/sda + update-grub within a chrooted environment it boots grub in recovery mode saying "File not found."

The disk is partitioned as follows:

/dev/sda1:    ntfs,  1.5GB, SYSTEM DRV
/dev/sda2:    ntfs,  150GB, Windows7 OS
/dev/sda3:    extended
  /dev/sda6:  ext4,  140GB, Ubuntu 12.04
  /dev/sda5:  ntfs, 10.7GB, Lenovo Recovery
/dev/sda4:    ntfs, 16.8GB, a custom additional partition

I guessed that the partition labelled "SYSTEM DRV" may be the EFI partition, but then I read that the EFI partition is of type FAT32. I don't have any FAT32 partition here!

So I can't follow any How-Tos explaining how to install Grub2 with EFI support. They all want me to mount my EFI partition at /boot/efi. I also can't just create an EFI partition since in most How-Tos they say that it should be the first partition (at least it has to be a primary partition), but as you see I already have a partition 1.

Isn't it possible to just use the normal Grub2 tool on EFI hardware?

If not, will creating an EFI partition solve the problem? Can I use partition 4 for that?

My BootInfo as created by using this article can be found here: http://paste.ubuntu.com/1011739/. Note that is being made from a Ubuntu Live USB drive which was at /dev/sdb, so you should ignore this drive.

UPDATE:

As EFI doesn't seem to be the problem here, I reinstalled (non-EFI-)grub using boot-repair.

New BootInfo can be found here: http://paste.ubuntu.com/1012223/.

Problem is now, that BIOS doesn't boot but gives the error:

Operating system not found.

UPDATE 2 (SOLUTION):

When you read this question when having the same issue (Operating system not found.), you might miss the forest for the trees when reading the answers, so I repeat the solution here:

The problem in my case was, that I accidently changed the boot flag of the drive to /dev/sda6, which is a logical partition. BIOS searches for boot flags on a hard drive it wants to boot from, but only looks in primary partitions. If it can't find a boot flag, it skips the hard drive. If it doesn't find any drive or media to boot from, you see the error "Operating system not found."

I use Ubuntu 12.04 on a home server. There are 5 hard drives: one SSD with the OS and 4 HDDs (Samsung HD204UI) configured as a RAID5 using mdadm.

I don't need the RAID very often (say, about once per day in average); it contains multimedia data and some backups, so I decided to put the drives to standby most of the time.

I configured the drives to automatically spin-down after 20 minutes using hdparm, here /dev/sda as an example:

hdparm -S 240 /dev/sda

The output of the command confirmed this:

/dev/sdb:
 setting standby to 240 (20 minutes)

But the problem is that the drive spins down after about 5 seconds (instead 20 minutes) after the last access, and

hdparm -C /dev/sdb

displays:

/dev/sdb:
 drive state is:  standby

Why doesn't the drive wait the 20 minutes as configured? Does it have something to do with the RAID setup? (I don't think so...)

This very short timeout is problematic since it is a RAID5 and when I access a file, it is spread block-wise around the four drives. Since drive 1 isn't needed when drive 2 is read, it went asleep when it will be used the next time (after drive 3 has been read from). So the drives keep spinning up and down the whole time resulting in a throughput near zero.

For the people being concerned about the life of my drives: It will be no problem that the drives are spinned up and down once a day in average since I prefer saving energy and heat over health of the drives (I use RAID5 and the content isn't very important).