Category Archives: troubleshooting

Mails appearing from d1stkfactory

If you have a Debian machine and emails appear to be coming from hostname @d1stkfactory, edit /etc/mailname and set this to your actual FQDN. Another instance where I found it locally is in /etc/exim4/update-exim4.conf.conf, which is almost certainly not read by my installation of Postfix (which does explicitly refer to /etc/mailname in one place).

This appeared on a machine running on DigitalOcean, so I presume “d” refers to DigitalOcean, and “factory” refers to their internal disk image building service. That’s just speculation though.

Ubuntu, touchscreen and dualscreen: HD Touchscreen on the left, laptop on the right

If you read about calibrating touchscreen with X11 and are capable of simple addition and division, you won’t have a problem building the transformation matrix and applying it. I won’t cover the same details on how to set the matrix using xinput set-prop since I just want to write down the resulting matrix and, perhaps, save people some time if they have a setup similar to mine.

To get the name of the device, open Terminal and punch in:


In the output I found that my “Acer T232HL”‘s input component is actually called “Advanced Silicon S.A CoolTouch(TM) System”. I can see all of its properties with:

xinput list-props Advanced Silicon S.A CoolTouch(TM) System

Since I’ve set up the screen to be on the left site, that means top-left corner of my touch area is simply offset by 0,0, and bottom-right is 1920,1080. Considering that the total width of the usable X area is 1920+1280, I get 1920/3600=0.6 as the c0 constant on the above link.

My usable area’s height is max(1080, 800) (the respective y component of the resolutions of the two displays). Considering that touch area’s height is also 1080, then the c2 component does not need to be scaled and should be exactly 1.

I also have absolutely no offsets, so c1 and c3 stay 0.


xinput set-prop "Advanced Silicon S.A CoolTouch(TM) System" --type=float "Coordinate Transformation Matrix" 0.6 0 0 0 1 0 0 0 1
# And if needed, to make the display configured as described above:
xrandr --output DP-0 --auto --left-of LVDS-0

From the times when I was trying to get Linux to run on iPaq H3800 devices using the kernel and distributions published at the now-defunct, I remember the “tslib” which included a touchscreen calibration tool. I wonder if that can and should be used to calibrate the modern multitouch displays.

Update (April 5th 2014): I just dug out package ‘xinput_calibrator’ by random googling, but have not tried it out yet.

Ubuntu 13.10 live CD: Blank screen with EFI

Ubuntu 13.10 fails to start X11 on a Macbook Pro with retina display, and it fails to start X11 on VirtualBox when EFI mode is turned on. Even the failover mode fails. This has been tried with 64-bit version of Ubuntu 13.10. Machines: a 2013 Macbook Pro; and a virtual VirtualBox 4.3.6 machine configured for Ubuntu (64-bit) OS, with EFI turned on.

Ubuntu’s failover configuration tries to use vesa module, which is not available when running under native EFI or UEFI mode.

Let’s fix this by using fbdev module.

  1. Hit ctrl+alt+f1 to switch to console.
  2. Type sudo -i to become root.
  3. Now let’s fix the relevant files:
    cd /etc/X11/
    sed 's/Driver.*"vesa"/Driver "fbdev"/' xorg.conf.failsafe > xorg.conf
  1. Restart X11 et al: service lightdm restart
  2. If necessary, switch to the VT dedicated to X11: hit ctrl+alt+f7

Note that the screen will stay blank for a while longer; give the system some time to proceed.

Good luck!

Few notes on UPC Ireland’s Technicolor TC7200

Based on this thread which I ran into here. These are just notes; if you can learn something from them, do so; but please be careful and fully aware that these are not instructions — merely notes for my own personal use in the future. I do not recommend you follow the notes; quite the opposite.

Despite (according to their reps on Twitter) telnet being unsupported by UPC, you can easily telnet and use username: webstar, password: webstar to log into the console. There isn’t much to do there, sadly. Apparently you may be able to use the set command to control SNMP settings.

Some configuration of hidden features can be done via SNMP. I highly advise you not to do that. This is unsupported by UPC, and you might be unable to restore settings to the previous state.

To switch the device into pure modem, non-routing mode, supposedly you use:

snmpset -v2c -c public i 1

This didn’t work for me immediately. It seems to work immediately after reboot. Also worth noting is the snmpwalk command:

snmpwalk -v2c -c public

Note that the value of “1″ means “modem mode” (also known as “bridge mode”), while “2″ means “ordinary NAT+routing mode”.

Be very careful. Turning on “modem mode” breaks Wi-Fi. You may need to bring up a separate access point for Wi-Fi. You may have trouble restoring the setting. PUBLISHING OF THESE NOTES DOES NOT CONSTITUTE ENDORSEMENT TO ACTUALLY USE THEM.

Also, I was unable to restore the setting to “2″ using SNMP. Hard reset by holding the reset button for 30 seconds worked. Unless you use it strictly as a modem, with another device that performs NAT and IPv6 routing, it isn’t worth switching to NAT mode. So please don’t do this unless you’re fully prepared for breakage of service and possibly annoying UPC (since they obviously don’t want people to play with this).

It’s interesting that UPC does assign a public, fully routable IPv6 /64 prefix. Too bad that it’s not exposed to regular users locked behind a NAT who cannot get direct access to the public Internet, and who have been locked out of it by a firmware that is seemingly arbitrarily restricted compared to the one used in Netherlands. UPDATE: Two sources have told me that they did not receive an IPv6 prefix or address. As I am not keeping my device in bridge mode, and I do not advise readers to do so either (unless they have very good reasons), I cannot and won’t verify this. You can opt to leave a comment on your success, but I want to be clear that neither my text, nor any comments below, represent any advice on my part.

It’s also interesting that the setting seems to have survived a factory reset through the web interface. Factory reset through web interface has, however, restored WiFi functionality, and it seems that WiFi and LAN are getting separate IP addresses. Factory reset by holding the reset button for 30 seconds is the actual hard reset and cleans up the setting for “modem mode”.

About downtime on my blog: lack of RAM and swap! Also, what is “swappiness”

Over the last few days I had a bit of downtime. I have no monitoring set up for the services, and I didn’t have problems on the previous server. But having migrated to DigitalOcean, it turns out that its default configuration does not provide a swap partition, and that 512mb is too little for Apache2 and MySQL (at least with configurations I had on the previous server).

Even after a bit of reconfiguration to tell both Apache2 and MySQL to back off a bit, every few hours Linux would choose MySQL as the “less important” process to kill, due to lack of memory. And MySQL would not automatically restart (because it’s not set up to do so).

So I’ve done some deleting of old hosted files (freeing up a bit of disk space) and have set up a 1gb swapfile (note that the instructions are intended for 256mb servers, hence creating a 512mb swapfile).

In the process, I learned about sys.vm.swappiness, which is a kernel setting that apparently controls when the kernel will decide to swap things to the swap partition or swap file. By default set to 60, as the article instructs I’ve set it to 0 (which makes sense, as I want swap to be used as rarely as possible). IBM also suggests 0 in KVM-based virtual machines which is also what DigitalOcean uses.

This article from 2007 suggests you may even want to increase it in some cases (when you have a lot of inactive jobs waiting to be run), and force kernel to more aggressively find unused memory pages that it can swap to the disk. This AskUbuntu answer has a good explanation on what swappiness means: a setting of 60 means that at 40% usage kernel will attempt to find inactive pages to swap, and a setting of 10 means that at 90% usage kernel will attempt to find inactive pages to swap. Wikipedia also has an article, which sadly does little to explain the actual mechanisms.

A better solution would be to force MySQL and Apache2 to use appropriate amounts of RAM (and abide by some absolute limits, such as 196mb+196mb). But that’s something I’ll play with on another day… there are more important things to work on right now. ;-)

apr-1-config broken under Mavericks

UPDATE October 23 2013 As commenters point out below, simply installing Xcode 5.0.1 and its Command Line Tools is enough. I’ve finally got around to testing out the suggestion provided to me almost two weeks ago, and it worked.

The content below is preserved for posterity. Please just install Command Line Tools and see if that helps.

Is perhaps brew install serf or brew install subversion broken for you on Mavericks? Or generally apr-1-config seems to return spurious results referring to nonexistent locations in /usr/include or to OSX10.9.xctoolchain?

While Apple does not recommend touching any system file or folder as they may and will be overwritten during OS upgrade, consider editing the following lines:

-CPP="/Applications/ -E"
+CPP="/Applications/ -E"

Now that I have serf package installed, all I have left to figure out (or get someone else to figure out!) is subversion. Only then I might have some hope of getting hgsubversion to work again and getting some work done without resorting to Subversion directly.