Sync clock with Google

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If the Linux VM was running at the time the host OS (Windows) hibernated then the clock in the guest VM will be left at the time of hibernation. If NTP is configured then the clock should resync gradually but most systems do not apply a big chunk of time correction by default.

If the Linux VM was configured with a VPN that implements a system-wide configuration then the DNS resolution might be unable to resolve the NTP server since the DNS of the VPN session will be unavailable. The alternate and work-around presented hinges on two things:

  • The guest VM has internet access at the time it was resumed.
  • The google.com domain name is already resolved and cached.

   sync-clock() {
     echo Current time before sync: `date`
     echo Current time after sync : `sudo date -s "$(wget -qSO- --max-redirect=0 google.com 2>&1 \ 
       | grep Date: | cut -d' ' -f5-8)Z"`
    }

The work-around uses the time in the google headers to provide an anchor for the correction.  This is provided as a bash function to provide user feedback if a correction was done.

Snippet execution

Fix for crashing gnome-control-center

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The GNOME control center in my Manjaro system crashed while I was tweaking the details of the mouse settings. After it crashed, I was unable to bring it up again even after a reboot.

The solution was to reset the configuration files for it using the following command:

$ dconf reset -f /org/gnome/control-center/

After that, the control center UI is up and running again. Based on the search hits, visiting the details pane can sometimes caused the state that results to a segmentation fault whenever the control center initializes.

We welcome our new overlords

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I heard in a Technology training that “It is hard to comprehend that there will come a time that Artificial Intelligence (AI) will get smarter than us humans but it may still be about 50 more years.”

I find that preposterous. AI by definition isnt going to be smarter than human intelligence. It doesnt need to be. Humans on the other hand will just grow dumber. Technology helps.

Docker image cleanup

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Running docker frequently can lead to mysteriously disappearing space. I kid, its not mysterious. Each image builds a layer which in turn eats up space. Logical but PITA!

Put this in your .bashrc or run it as cron on your docker host to clean up.


docker rm -v $(docker ps -a -q -f status=exited)
docker rmi $(docker images -f “dangling=true” -q)

or do it in one alias (use at your own discretion)


alias docker_janitor='docker rm -v $(docker ps -a -q -f status=exited);docker rmi $(docker images -f “dangling=true” -q)'

sounds too easy..

ciao!

Ubuntu 15.04 hanging boot-up issue

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Last weekend I reinstalled my Linux system (and not because I want to rename it as Pyg!) which is a very bad decision as it is the same time that my pitiful internet connection fails to transmit any data beyond a few bytes. The new install to Ubuntu 15.04 (Vivid Verve) gave me the confidence to start using btrfs which is being touted as the next generation file system for linux systems. Bad move and very short-sighted on my part. 🙁

The btrfs is supposed to provide enhancements to ext4 file system since it (btrfs) is built from the ground up but with the useful features already present in ext4. The ext4 filesystem is basically being viewed as an aging hack on a hack since it builds on ext3 which is a tack-on improvement for ext2. Btrfs might be delivering on some of its promised features but those who use it should still be wary of it as it is still not considered as ready for “production” or real-world use[1]. I wish I knew this before I chose it as the filesystem for my home directory. 🙁

For those that will have the misfortune of encountering it, the gist of my predicament follows (which is based on how I remember it):

  • I upgraded my system using dist-upgrade.
  • I encountered a severe freeze which left me with no choice but to reach for the power button.
  • System bootup hangs. The last entry goes something like this:
  • A start job is running for /home… (10s /no limit)

  • Eventually the bootup hangs and it drops the control to an emergency shell.

It was unnerving for me since a reinstall means I would need to re-download the upgrade packages on my #@$@#$ Smart LTE connection. The light-bulb moment for me was that /home is the only partition in the sequence that is using btrfs. The working theory is something borked during the forced shutdown which should have been handled by the journalling features. Thanks to an alternate albeit slow alternative connection, I was able to google enough to do the following:

  • Boot the machine and press F12 after the BIOS/UEFI prompt.
  • Selected the menu option for Ubuntu Advance options.
  • Selected the option for “(recovery)”
  • Selected the “drop to root shell” option.
  • Remounted the root system in r/w mode. I dont think this is needed but this is what I have done and it won’t hurt anyhow.
  • # mount -o remount,rw /

  • Did a btrfs file system check on the home partition
  • # btrfsck /dev/sda4

  • When nothing popped out, I went for the repair option.
  • # btrfsck --repair /dev/sda4

The repair option is always accompanied by a cautionary warning as it can delete information so having a proper backup is recommended. In my situation that is like adding salt to the injury. When I ran the repair option it reported that the cache and super generation areas do not match and that it cleared the space cache. After doing so I ran another btrfsck on the partition and rebooted the system which thankfully landed me on a working system with no (identified) data loss.

The moral of the story is to select btrfs only for the filesystems that you can afford to lose data; or have a good backup scheme. Using it for /tmp is going to be an overkill but to each to his own. Now Im thinking if I want to convert my home partition back to ext4. 😀

ciao!

[1] https://www.wikivs.com/wiki/Btrfs_vs_ext4

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