Archive for the ‘Linux’ Category

Using GNOME 3 (GNOME shell) with a VNC client

Monday, April 13th, 2015

Sometimes I have a need to access a running GNOME 3 desktop from another client running GNOME 3, using VNC. This can be tricky since GNOME 3 is heavily dependent on the use of the “Super” (Windows) key and even when you are using the remote machine’s desktop, pressing the Super key results in the local GNOME overview being brought up. Similarly for Alt-Tab, you end up switching local applications rather than applications on the remote desktop.

After a bit of searching I found a question about remapping the Super key on The question is what to remap it to (I didn’t want to disable it altogether).

Sharing the best solution I found, I found the following sufficient to get a usable remote desktop:

  • Remap the “Super” key on the remote desktop to the “Menu” key (if the local client has that key) – gsettings set org.gnome.mutter overlay-key “Menu”
  • Using the GNOME 3 keyboard settings, in Shortcuts -> Mapping -> Navigation, change “Switch Windows” from Alt+Tab to Ctrl+Tab.

This doesn’t solve everything, perhaps due to the way keyboard combinations are handled with VNC e.g. the menu bar can’t be brought up by <Menu>+M, but it’s good enough.

In this case the local machine was running Fedora 20 and the remote machine RHEL7.

I/O performance of self-built low-power Linux home NAS

Friday, August 29th, 2014

So, my article about building a low power Linux home NAS got quite a lot of attention, and several commenters wanted information about the performance.

I/O performance was something that I was curious about it when I built it, especially if using encrypted disks (LUKS) with such a low-power machine, so I did some very basic tests and the results are below. All tests are done with a large (3.5GB) file/data, intentionally larger than the memory. They involve writing to an ext4 filesystem (default configuration with RHEL6) sitting over a RAID0 MD array. Disks are 2 x Seagate SpinPoint M8/ST1000LM024 1TB 2.5″.

I’ve got to emphasise that these are quick and dirty initial results to give an idea; I’ve not analysed them deeply and there might be methodological flaws (e.g. I didn’t force caching off)

Sequential read/write (dd)

Non-encrypted Encrypted (LUKS)
Block size (bytes) Read (MB/s) Write (MB/s) Read (MB/s) Write (MB/s)
4096 43.9 21.7 1.4 11.1
8192 52.7 38.2 20.3 15.3
65536 51.6 45.0 26.5 21.1
131072 51.1 45.5 27.1 22.0