A Weird Imagination

Timezones and scheduling tasks with at

The problem

My system for automatically posting future-dated blog posts mysteriously stopped working recently. The posts would appear if I manually published the blog, but not with the automatic scheduling mechanism.

The solution

In schedule_publish.sh, I changed the line

echo "$0" | at -q g $time

to

if [ "$(date -d "$time PST" +'%s')" -ge "$now" ]
then
    echo "$0" | at -q g -t "$(date +'%Y%m%d%H%M' -d "$time PST")"
fi

(where "PST" is the timezone of this blog; adjust as appropriate for your blog). $now is initialized with

now="$(date +'%s')"

before the call to make publish to avoid a race condition.

The details

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PulseAudio headphone jack troubles

Posted in

The problem

Since I got a new motherboard (and therefore new audio hardware as I'm using the basic one built into the motherboard) sometimes after I unplugged my headphones, my speakers would not output any sound.

pavucontrol showed the only available output as "Built-in Audio Digital Stereo" with a port of "S/PDIF", which does not describe any audio device I had ever used. If I plugged my headphones back in, they would work fine, and usually after unplugging and plugging back in my headphones enough times, my computer would eventually acknowledge that my speakers were connected by showing the expected "Built-in Audio Analog Stereo" with a port of "Line Out".

The solution

In /usr/share/pulseaudio/alsa-mixer/paths/analog-output-lineout.conf change

[Jack Front Headphone]
state.plugged = no
state.unplugged = unknown

to

[Jack Front Headphone]
state.plugged = no
state.unplugged = yes       # changed from unknown

This forces PulseAudio to consider there to be speakers plugged into the "Line Out" port, so it may cause strange behavior if that is not the case.

To apply the change, run

pulseaudio --kill
pulseaudio --start

to restart PulseAudio.

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Nvidia GLX not working

The problem

I recently replaced my old Nvidia graphics card with a newer one. Upon booting up, I ran glxgears to test that 3D graphics were working properly and got an error like

X Error of failed request:  BadWindow (invalid Window parameter)
 Major opcode of failed request:  155 (NV-GLX)
 Minor opcode of failed request:  4 ()
 Resource id in failed request:  0x1200003
 Serial number of failed request:  34
 Current serial number in output stream:  34

The solution

Either delete /etc/X11/xorg.conf or edit it and remove (or comment out) the "Files" section; that is, the lines

Section "Files"
    ...
EndSection

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Application bypassing PulseAudio

Posted in

The problem

Recently I ran a game1 and instead of the expected music, got distorted noise. At first I thought there was something physically wrong with my speakers or the connection to them, but running any other program resulted in normal sound, albeit mixed with the distorted sound of the game. Even more strangely, changing the volume in the game changed the volume of the distorted noise, implying the game was in fact generating the right thing but it was being misinterpreted, so the culprit was neither the game nor the sound driver but somewhere in between them.

As I had recently set up PulseAudio2, I suspected it was to blame. I opened up pavucontrol to find the game omitted from the list of applications producing sound, which suggested the problem was caused by the game trying to use some way to produce sound that PulseAudio was not capturing.

The solution

The short version is that the problem was solved by restarting PulseAudio:

$ killall -9 pulseaudio

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SDL screensaver hangs on exit

The problem

I was modifying a screensaver written using SDL and noticed that sometimes there were many instances of it left running, even after unlocking the screen. Another bug was causing the screensaver to use 100% CPU, resulting in it using up all of my processing power just for a simple screensaver.

The solution

Make the program exit immediately when it receives a SIGTERM signal by including the function

void exitImmediately(int sig) {
    abort();
}

and making the SIGTERM signal handler call it:

signal(SIGTERM, exitImmediately);

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