Monthly Archives: September 2017

Shifting laptops in Ubuntu

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My laptop HDD was failing and getting worse. Time to get a new machine and shift. Here is the highly simplified, sanitised version of how I got everything working.

Install latest Ubuntu (finally shifted from 32 to 64 bit). Use https://etcher.io/ to make live USB – it Just Works™. Was given the option of retaining Windows 10 so gave it 84GB/2TB and kept rolling.

Sorted out Nvidia as per Ubuntu 16.04LTS extended display not working (see also https://www.youtube.com/watch?v=_36yNWw_07g)

  1. Run sudo apt-get purge nvidia-*
  2. Run sudo add-apt-repository ppa:graphics-drivers/ppa
  3. Run sudo apt-get update
  4. Run sudo apt-get install nvidia-364 (Check what’s the latest version… in my case nvidia-375 was the latest in the repos)

Reboot. Success?

Set up launcher etc so not sticky and icons the right size. Remove unneeded ones etc.

sudo apt install chromium-browser dh-make gftp gimp git idle3 imagemagick inkscape keepass2 mysql-server openjdk-9-jdk python3-matplotlib python3-nose python3-numpy python3-requests python-pil python-wxgtk3.0 python-wxversion p7zip-full scribus shotwell shutter sqlitebrowser synaptic thunderbird vim virtualbox virtualbox-guest-additions-iso vlc wine64-development hardinfo

I got SQLYog working. It was fun finding the icon. Run using wine sqlyog.exe etc rather than trying to double click exes.

For MySQL I copied everything over and sorted out permissions. The innodb tables wouldn’t run (tables apparently did not exist) but I didn’t actually need them given they were local copies of remote tables. So I just transferred databases over using SQLYog.

For my cron jobs I ran crontab -e on source laptop and stored results then ran same command on new machine and pasted them. How cool is that :-).

Installed newest version of eclipse. As always, some faffing around to get desktop file sorted out etc. E.g.

sudo ln -s /home/g/eclipse/java-oxygen/eclipse/eclipse /usr/bin/eclipse

Install pydev.

Brought across lots of documents of course, and .gftp, .idlerc, .matplotlib, .openshot, .shh. Plus Music, Videos, Pictures (including photos)

Added thunderbird and firefox to startup.

Changed LibreOffice icon style to Galaxy under Tools>Options>LibreOffice>View>Icon style.

Then run some backups.

WiFi changes – printer stops working

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My parents-in-law changed over their WiFi and their router. So the wireless printer stopped working. The solution was simple – we just needed to connect the printer to the new WiFi using the latest ssid and key (password).

Being a Canon MG7160 the first step was to swipe left or right on the printer touchscreen at WLAN, then Wireless LAN Setup > Standard Setup > and the ssid. Enter passphrase. Now the printer can connect to the WiFi and you can print to it over the WiFi.

ImageMagick cache resources exhausted resolved

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My sofastatistics application relies on ImageMagick to convert PDFs to PNGs. The sort of command run under the hood was:

convert -density 1200 -borderColor "#ff0000" -border 1x1 -fuzz 1% -trim "/home/g/projects/sofastats_proj/storage/img_processing/pdf2img_testing/KEEPME/raw_pdf.pdf" "/home/g/projects/sofastats_proj/storage/img_processing/pdf2img_testing/density_1200_fuzz_on_#ff0000.png"

Recently, commands like this stopped working properly on my development machine. They wouldn’t handle high resolutions (600dpi seemed to be the limit for the images I was handling) and it took a very long time to complete.

I finally worked out what was going on by running the same tests on different machines.

Seemingly modest differences in CPU specs can create massive differences in the time required to convert PDFs to PNGs. What takes 4 seconds on an i7 can take 71 seconds on an i5. And creating a 1200 dpi image might take 0.5 minutes on an i7 and 18.5 minutes on an i5. So the slowdown was because I had shifted from a fast desktop to a (more convenient but slower) laptop.

The second issue was the error message about cache resources exhausted. This happened on a range of fast and slow machines and the amount of RAM seemed irrelevant. Interestingly, the problem only occurred on Ubuntu 17.04 and not 16.10. The reason was the policy.xml settings in /etc/ImageMagick-6/. It seems the following was set too low:

<policy domain="resource" name="disk" value="1GiB">
I changed it to:
<policy domain="resource" name="disk" value="10GiB"/>
and it would successfully create high-resolution PNGs even if it took a long time.

Hmmm – now I change the disk setting back and I am still able to make the higher-resolution images, even after rebooting. WAT?!

One other note – settings in policy.xml cannot be loosened through arguments supplied to the convert program via the CLI – they can only be tightened. It looks like these changes are all about security concerns with the intention of preventing malicious resource starvation.

Some references: