Tuesday, September 1, 2020

Running jackd command line works, but not via systemd because [Cannot allocate memory]

I am working on a personal project with my husband (also a software dev), where he got the video saving piece working with a raspberry pi, python, and picamera.  Audio wasn't working yet, so I decided to take that piece on.

Raspberry Pi 2 Model B
Raspberry Pi USB WiFi Adapter
Raspberry Pi OS 10
Python 3.7.3
systemctl --version => systemd 241 (241)

I'm currently working with JACK audio server and jack_capture to capture audio files with JACK.   The jackd2 package installation included the /etc/security/limits.d/audio.conf.disabled file, which when activated, enables realtime permissions and memlock permissions to the audio group.  You can activate it via the following command or rename the file without the .disabled extension at the end.  Make sure to logout and login again for the audio server to have the configuration recognized - no need to reboot/restart.

dpkg-reconfigure -p high jackd
I installed jackd2 via the following commands:

# audio server
sudo apt -y install jackd2
# modify /etc/security/limits.d/audio.conf to bring realtime priorities to the audio group (which is usually fine for a single user desktop usage)
sudo mv /etc/security/limits.d/audio.conf.disabled /etc/security/limits.d/audio.conf

The audio.conf file configures the following; I verified the default pi user is in the audio group.

@audio   -  rtprio     95
@audio   -  memlock    unlimited

I installed jack_capture via the following commands.  The liblo-tools were necessary for me to remote control jack_capture via UDP port with OSC (Open Sound Control) messages.

# audio capture
sudo apt -y install liblo-tools
sudo apt -y install jack-capture

Starting jackd with python via command line worked great!  When I started the python script as a service with systemd this error kept occurring:

Cannot lock down 13589280 byte memory area (Cannot allocate memory)

Why?!  I read through numerous jackd configuration articles.  Running command line was fine.  Checking "ulimit -l" was unlimited (as the audio.conf file told the machine to do).

I stumbled upon this and this article (looked very old but it still applied for my problem!) that pointed me in the right direction that "When using the RPM or Debian packages on systems that use systemd, system limits must be specified via systemd."  Essentially running jackd with systemd ignores the audio.conf file, so you must set it manually with systemd.

# The four settings under Service is for jackd support
# LimitRTPRIO and LimitMEMLOCK must be set in systemd service file, because when run as a service
# etc security limits.d audio.conf is not honored.  MEMLOCK unlimited is infinity in systemd


  • The LimitMEMLOCK is set to "infinity" for the systemd service, but in the audio.conf was set to "unlimited". 
  • The two environment variables DISPLAY and JACK_NO_AUDIO_RESERVATION were set to get rid of these two errors I had previous to the "Cannot allocate memory error".
To bypass device reservation via session bus, set JACK_NO_AUDIO_RESERVATION=1 
Failed to connect to session bus for device reservation Unable to autolaunch a dbus-daemon without a $DISPLAY for X11

These additional articles were helpful:

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