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Joshua D. Boyd
Asked: 2020-05-28 14:03:53 +0800 CST

Set sysfs network option before interface is up

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I want to set /sys/class/net/wwan0/qmi/raw_ip, and I don't want to do it by writing a shell script to take wwan0 down set it, then put wwan0 back up as a systemd unit. I'm trying this on Raspbian Stretch, but I doubt the distribution matters much for this.

I tried a bunch of ways of expressing this as a kernel cmdline argument, with no luck (net.qmi.raw_ip=Y, net.qmi_wwan.raw_ip=Y, qmi_wwan.raw_ip=Y, etc).

I tried adding net.wwan0.qmi.raw_ip=1 to /etc/sysctl.conf. That produced this error: [ 23.918756] qmi_wwan 1-1.5:1.3 wwan0: Cannot change a running device
Which means that it didn't do it until wwan0 was already up.

I tried adding denyinterfaces wwan0 to /etc/dhcpcd.conf, but same result.

linux configuration-management sysctl dhcpcd

1 Answers

  1. You can try setting echo Y > /sys/class/net/wwan0/qmi/raw_ip inside your rc.local.

    A more convenient solution is to add the above line to the qmi shell script and finally call this during your ifdown & ifup actions on the interface.

    For more information refer to this guide: https://embeddedpi.com/documentation/3g-4g-modems/raspberry-pi-sierra-wireless-mc7455-modem-raw-ip-qmi-interface-setup

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