Wednesday, February 15, 2017

Disabling auto-window maximizing

I use Mate on Ubuntu and I don't run compiz.  This fix is specific to Mate without compiz.

Sometime in the recent previous Ubuntu versions, Unity (and other things that depend on the gnome libs, I guess) implemented window auto-maximizing when their upper edge touches the top of the screen (or the bottom of the top panel).  This may also affect the left and right edges of the screen, but it was always only a problem for me with the top edge.

To fix this in Mate:

System >  Preferences > Look and Feel > Mate Tweak

select Windows

and uncheck enable window snapping.

Thursday, September 15, 2016

OOM during rsync with USB drives

I had a (maybe/probably) dying external USB drive. It's part of a non-RAID LVM so I needed to grab everything off it before it died. I mounted a second external USB drive and started an rsync job to copy everything from the failing drive to the new one. After copying around 250GB the rsync would fail with an oom. 

Subsequent attempts would fail the same way but much more quickly. Running rsync with ionice -c 3 doesn't help (suggested in an ubuntuforums post), I wasn't using any of the options that would make recursiveness non-incremental. 

 I tried quite a few things (including --delete-during so that successive rsync attempts would have fewer files to keep track of) but finally found the solution. 

While rsync is running in one screen window, in a separate screen window I run: 

while true
  echo 3 > /proc/sys/vm/drop_caches
  sleep 2

There may be interaction between the USB drivers (perhaps timing/slowness?) and the memory used by the buffer caches. Perhaps when rsync needs memory the kernel isn't able to free it fast enough and the oom killer steps in before the memory becomes available to give to rsync? 

In any case, with this drop_caches loop, rsync is now running happily for hours. I expect it'll actually finish. I don't mind the loss of caching. It's only for very large copies from USB drives and the copies are reading everything sequentially.

There won't be much of a benefit to caching. Perhaps I could use just "1" though instead of "3", so that we'd keep inodes and dentries in the cache. But the limiting factor here is really USB transfer rate and the transfer rate while dropping caches is just the same as the rate when not dropping caches (before oom).

Sunday, July 31, 2016

Building a mainline kernel for the odroid

Shuah Khan has a howto on building a 4.x mainline kernel for the odroid XU4.  That was very helpful when I built the mainline kernel for my odroid XU3.  I've also got an odroid U3 that I'll be upgrading soon.

I wrote a little shell script to let me do most things automatically (because I needed to rebuild the kernel a few times, adding features that I needed).

Mainly I needed ecryptfs support, iptables modules and some cgroups options for unprivileged lxc containers.  Also a little modification to set the default cpufreq governor to ondemand instead of performance.  I'll update this post at some point to document which additional options I enabled to get all of those things.

I've seen a few more minor patches elsewhere that I'll want to test out.  In particular I'll look for the Mali GPU driver config fix to set it to either not run at all or to run at its lowest energy level (because I don't use that at all, these odroids run headless).

A list of things that I've needed to enable (I'm adding items as I find missing items and rebuild the kernel iteratively :-):

ecryptfs support


tun device for openvpn


IO accounting stuff for iotop


netfilter/iptables modules

  • most things in IP: Netfilter Configuration
  • most things in IPv6: Netfilter Configuration
  • most things in Core Netfilter Configuration

user namespaces for unprivileged lxc


  • I forget if anything else was disabled in namespaces support, I just enabled everything under there.

veth support for lxc



# optionally, make menuconfig and set options.
# particularly for the cgroups stuff for unprivileged lxc and ecryptfs

make menuconfig

#make exynos_defconfig

make prepare modules_prepare
time make -j 8 LOCALVERSON="-tiger" bzImage modules dtbs

cp arch/arm/boot/dts/exynos5422-odroidxu3.dtb /media/boot/exynos5422-odroidxu3_next.dtb
cp arch/arm/boot/zImage /media/boot/zImage_next

make modules_install

apt-get install -y live-boot

cp .config /boot/config-`cat include/config/kernel.release`
update-initramfs -c -k `cat include/config/kernel.release`
mkimage -A arm -O linux -T ramdisk -C none -a 0 -e 0 -n uInitrd -d /boot/initrd.img-`cat include/config/kernel.release` /boot/uInitrd-`cat include/config/kernel.release`
cp /boot/uInitrd-`cat include/config/kernel.release` /media/boot/
cat include/config/kernel.release

echo "edit /media/boot/boot.ini"
echo "comment out the current setenv bootcmd and replace it with"

echo "setenv bootcmd \"fatload mmc 0:1 0x40008000 zImage_next; fatload mmc 0:1 0x42000000 uInitrd-`cat include/config/kernel.release`; fatload mmc 0:1 0x44000000 exynos5422-odroidxu3_next.dtb; bootz 0x40008000 0x42000000 0x44000000\""

Wednesday, May 18, 2016

x11vnc xauth

I've had problems lately starting x11vnc (to connect to :0.0) when I'm starting it over ssh.  I don't want x11vnc running all the time, so I don't start it when I'm at work.  But when I need it I'm *not* on the desktop in question, instead I'm remote.

I found the solution at ubuntuforums:

I do run screen on the remote desktop (my work desktop), and I generally start screen when X is already up, so *that* has the correct $XAUTHORITY entries.  So I can just connect to the running screen instance and do:


That will have something (from the ubuntuforums link above):


and, from ssh, I can use that:

x11vnc -display :0 -auth /var/run/gdm/auth-for-fred-s0G6r1/database

I should probably just have .bashrc detect if there's a $XAUTHORITY variable and if there is, echo it out to a file that I can then just source :-).

Friday, April 15, 2016

btrfs COW breaks Virtualbox

btrfs copy on write breaks VirtualBox so that starting a VM will often not complete due to spurious disk errors.

I'm trying out the chattr fix that turns off COW.

I've just done this:

cd ~/VirtualBox\ VMs

for f in `find . -name '*.vdi'`
  touch $T
  chattr =C $T
  dd if=$F of=$T bs=1M
  rm $F
  mv $T $F

Here's hoping it all works :-).  It's faster than mkfs.ext4 and restore from backup :-).

Tuesday, March 01, 2016

Lightning floating timezone warning

For the longest time (because I'm lazy), everytime thunderbird+lightning would start it would show three dialog box warnings about Unknown timezones being treated as the "floating" timezone.

This is easily fixed (in the sense that the warnings don't show anymore, and, given the nature of the fix, likely in the sense that timezone handling is now correct).

  1. Edit | Preferences | Advanced | Config Editor
  2. Click on the "I'll be careful" button.
  3. search for calendar.icaljs boolean value
  4. Set the value to true.