Sometimes a GUI is not the best way to control a computer's volume. Usually if you care about the volume of your computer, you're probably nearby but perhaps would rather be using a remote or other shortcut way of changing the volume. The specific use case that prompted this blog post was binding the volume up and volume down keys on my keyboard to the global volume control (as opposed to separately binding them in each application).
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 short version is that the problem was solved by restarting PulseAudio:
$ killall -9 pulseaudio
The Xbox 360 controller has become the defacto standard controller in PC gaming in recent years, likely due to both the popularity of the Xbox and the fact that the controller can easily be used with a computer. One downside of this is that some games assume you have one. If the game supports it and is running through Steam, then Steam's controller settings will let you use any controller, but that doesn't work for all games, and you might not be using Steam. The game that prompted this blog post actually does have Steam controller support promised in the future, but it's in early access and they are busy developing other parts of the game.1
xboxdrv#The solution is xboxdrv, the userspace
Xbox controller driver. In addition to supporting actual Xbox
controllers, it can also simulate Xbox controllers based on inputs from
other devices like a PlayStation controller or some less
common controller.
On a modern computer there are often many input devices,
$ ls /dev/input/event* | wc -l
28
They are just identified by numbers, so it can be difficult to choose the
right one and trial-and-error can get tiresome with so many. There is some
help from the by-id and by-path listings:
$ ls -go --time-style=+ /dev/input/by-id/
...
lrwxrwxrwx 1 10 usb-045e_0291-if06-event-joystick -> ../event26
lrwxrwxrwx 1 6 usb-045e_0291-if06-joystick -> ../js6
lrwxrwxrwx 1 10 usb-0b43_0003-event-if00 -> ../event20
lrwxrwxrwx 1 10 usb-0b43_0003-event-joystick -> ../event19
lrwxrwxrwx 1 6 usb-0b43_0003-joystick -> ../js1
lrwxrwxrwx 1 9 usb-BTC_USB_Multimedia_Keyboard-event-if01 -> ../event2
lrwxrwxrwx 1 9 usb-BTC_USB_Multimedia_Keyboard-event-kbd -> ../event1
...
$ ls -go --time-style=+ /dev/input/by-path/
...
lrwxrwxrwx 1 9 pci-0000:00:1a.2-usb-0:2:1.0-event-kbd -> ../event1
lrwxrwxrwx 1 9 pci-0000:00:1a.2-usb-0:2:1.1-event -> ../event2
...
lrwxrwxrwx 1 10 pci-0000:00:1d.0-usb-0:1:1.6-event-joystick -> ../event26
lrwxrwxrwx 1 6 pci-0000:00:1d.0-usb-0:1:1.6-joystick -> ../js6
lrwxrwxrwx 1 10 pci-0000:00:1d.0-usb-0:2:1.0-event -> ../event20
lrwxrwxrwx 1 10 pci-0000:00:1d.0-usb-0:2:1.0-event-joystick -> ../event19
...
But, for the most part, those names aren't very helpful, especially since many joystick devices support 2 or 4 joysticks connected to the same device.
identify_evdev.py#Enter identify_evdev.py:
$ identify_evdev.py
/dev/input/event22
Where /dev/input/event22 is the device of the joystick I touched after
running identify_evdev.py.
Linux has a tendency to give very unhelpful error messages when it is
unable to create a file. I previously blogged about a few
different reasons Linux might report a disk is full, but all of the
reasons included the disk actually not having space for more files. Yet
another reason to get similar errors is if the partition is
mounted readonly (ro):
$ mount | grep -F /usr
/dev/sdc2 on /usr type ext4 (ro,nodev,noatime,data=ordered)
mount without any options lists all of the mounted
partitions along with their mount options.
Many programs will show a helpful error message:
$ touch test
touch: cannot touch ‘test’: Read-only file system
But some others won't:
rtorrent: Could not lock session directory: "./session/", held by "<error>".
That error is normally caused by
./session/rtorrent.lock not being writable due to being held by
another process, but in this case it's not writable due to the
filesystem being readonly. rtorrent doesn't distinguish the two.
For that reason, when running into weird behavior from a program on Linux, it's a good idea to check that the directories the program might try to write to are actually writable.
I was having trouble with a USB joystick adapter
(an EMS Playstation controller adapter, to be specific). When
I plugged it in, it wouldn't work and checking dmesg
showed the same error getting generated over and over again (at least
once per second):
$ dmesg
...
[81700.968873] usbhid 6-1:1.0: can't add hid device: -71
[81700.968885] usbhid: probe of 6-1:1.0 failed with error -71
[81700.968986] usb usb6-port1: disabled by hub (EMI?), re-enabling...
[81700.968991] usb 6-1: USB disconnect, device number 53
[81701.208025] usb 6-1: new low-speed USB device number 54 using uhci_hcd
[81701.384866] usb 6-1: string descriptor 0 read error: -32
...
I decided the sensible thing to do was to reload the driver:
$ sudo modprobe -r usbhid # Bad idea, don't run this
PulseAudio is what most modern Linux distributions use as a sound server, the part of the sound subsystem that sits between applications and the sound driver supporting features like allowing multiple applications to output sound simultaneously. PulseAudio adds various features not present in other Linux sound servers like per-application volume controls and easily outputting to different audio devices (for instance, using HDMI audio instead of the normal audio jack).
PulseAudio can be controlled using pavucontrol,
which is a GUI audio mixer. It shows a volume meter and control for every
application producing sound as well as an option to choose which audio
device it is outputting to. It additionally lists all of the hardware
input and output devices, as you would expect from an audio mixer.
If PulseAudio is not working properly, you can restart it by running
$ killall -9 pulseaudio
No, really, that's what Debian's PulseAudio page says to do.
When I initially installed PulseAudio, it didn't have my sound cards listed and just had the default null outuput, making it not very useful. Running that command to restart it fixed it.
PulseAudio seems to mute my sound card all by itself. Currently, I just
go into pavucontrol and unmute it.
Normally with X, it's easy to run an application on a remote computer just by using X forwarding:
local:~$ ssh -X host
host:~$ echo $DISPLAY
localhost:20.0
host:~$ xterm
The xterm will appear on your local computer.
But if you want to continue working with that application on a different remote computer (or once you are physically in front of the computer it is running on), then you're out of luck.
For an application running in the terminal, you can start it inside
a GNU Screen (or tmux) session which you can
detach and then attach to again on another ssh connection.
xpra (X Persistent Remote Applications
) lets you
move graphical applications from one computer to another in addition
to fixing other problems with X forwarding.
If you instead use xpra for the forwarding, then you can detach
and reattach to the session at will.
Today I was borrowing a board game from the lending library at Emerald City Comicon and it was missing its dice. We could have gotten some physical dice somewhere, but instead we decided to use the materials we had on hand. The people I was playing with agreed that we did not want to drain our phone batteries by using a dice app on our phones, but I had a laptop with me. So I wrote a dice app for the shell:
while true
do
reset
seq 1 6 | shuf -n1
seq 1 6 | shuf -n1
read
done
This rolls two six-sided dice every time you hit enter and
clears the screen before showing the result using reset.
Trying to install the python-numpy package in
Debian Unstable ("Sid") I got the following error on the
liblapack3 package (seen also in this bug):
$ sudo apt-get install -f
Reading package lists... Done
Building dependency tree
Reading state information... Done
0 upgraded, 0 newly installed, 0 to remove and 36 not upgraded.
4 not fully installed or removed.
After this operation, 0 B of additional disk space will be used.
Setting up liblapack3 (3.5.0-4) ...
update-alternatives: error: alternative liblapack.so.3gf can't be slave of liblapack.so.3: it is a master alternative
dpkg: error processing package liblapack3 (--configure):
subprocess installed post-installation script returned error exit status 2
dpkg: dependency problems prevent configuration of python-numpy:
python-numpy depends on liblapack3 | liblapack.so.3; however:
Package liblapack3 is not configured yet.
Package liblapack.so.3 is not installed.
Package lapack3 which provides liblapack.so.3 is not installed.
Package atlas3-base which provides liblapack.so.3 is not installed.
Package liblapack3 which provides liblapack.so.3 is not configured yet.
Package libatlas3-base which provides liblapack.so.3 is not installed.
Run the following command to fix the error:
$ sudo update-alternatives --remove-all liblapack.so.3gf
And then rerun the install:
$ sudo apt-get install -f