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Mark Lee
Asked: 2020-05-31 07:52:14 +0800 CST

How do I automatically run modprobe v4l2loopback on boot?

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I'm using OBS Studio and would like to have a virtual video output saved permanently so that it can be run when the application is launched.

This command creates the virtual output:

sudo modprobe v4l2loopback video_nr=10 card_label="OBS Video Source" exclusive_caps=1

But I must run the command in console on each boot. How can I make this permanent? The plugin that utilizes the output in OBS Studio is configured to auto start but /dev/video10 is not available after a reboot of the system.

$ modinfo v4l2loopback | grep -i parm
parm:           debug:debugging level (higher values == more verbose) (int)
parm:           max_buffers:how many buffers should be allocated (int)
parm:           max_openers:how many users can open loopback device (int)
parm:           devices:how many devices should be created (int)
parm:           video_nr:video device numbers (-1=auto, 0=/dev/video0, etc.) (array of int)
parm:           card_label:card labels for every device (array of charp)
parm:           exclusive_caps:whether to announce OUTPUT/CAPTURE capabilities exclusively or not (array of bool)
parm:           max_width:maximum frame width (int)
parm:           max_height:maximum frame height (int)
modprobe obs-studio 20.04

2 Answers

  1. Best Answer

    Normally kernel modules can be added to /etc/modules for loading at boot time.

    Add this to /etc/modules...

    v4l2loopback video_nr=10 card_label="OBS Video Source" exclusive_caps=1

    However, I don't know if you can pass parameters there. So here's another way to do it.

    Add this to /etc/modules...

    v4l2loopback

    Create /etc/modprobe.d/v4l2loopback.conf

    options v4l2loopback video_nr=10 card_label="OBS Video Source" exclusive_caps=1

    Then...

    sudo update-initramfs -c -k $(uname -r)

reboot

    Confirm module loading with...

    lsmod | grep -i v4l2loopback
    • 9

  2. Easy way to do it un Ubuntu 20.04 and others:

    $ sudo echo "v4l2loopback" > /etc/modules-load.d/v4l2loopback.conf 
$ sudo echo "options v4l2loopback video_nr=10 card_label=\"OBS Video Source\" exclusive_caps=1" > /etc/modprobe.d/v4l2loopback.conf

    You can restart to check it works!

    NOTICE

    Be aware of a bug on v4l2loopback-dkms 0.12.3-1ubuntu0.1

    More info on this stackoverflow post.

    EDIT - Using tee

    As pointed by renyhp, it's better to use the tee command:

    $ sudo echo "v4l2loopback" | tee /etc/modules-load.d/v4l2loopback.conf 
$ sudo echo "options v4l2loopback video_nr=10 card_label=\"OBS Video Source\" exclusive_caps=1" | tee /etc/modprobe.d/v4l2loopback.conf

    EDIT - Update modules

    As commented, it seems that in some systems after rebooting some problems can be experienced. To avoid that, it's always a good idea to update the modules:

    sudo update-initramfs -c -k $(uname -r)
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