udev_monitor

Monitor linux udev events and execute actions on detection

Designed to execute actions when USB devices are plugged-in / removed

udev_monitor works with Linux udev and monitors it's events. Upon a specific event for a given device (in VENDOR_ID:PRODUCT_ID format), it will execute an action.

udev_monitor has been used to:

• Re-attach USB devices to virtual machines after they're unplugged - plugged in again
• Run a full USB reset when device is plugged in (fixes some of the USB UPS that identify as Cypress Semiconductor USB to Serial)

Setup

pip install udev_monitor

Quickstart example

This is a realworld example to detect most USB UPS and execute a script upon plug-in.

Run script /usr/local/bin/restart_nut_driver.sh with argument 0665:5161 everytime USB device with vendor id 0665 and product id 5161 is added or removed

udev_monitor --devices 0665:5161 --udev-actions add,remove --filters=usb --action /usr/local/bin/restart_nut_driver.sh

Full usage

--devices           List of comma separated devices to monitor. Example:
                    '0665:5161, 8086:1234'
                    If no devices are given, all devices are monitored.
--udev-actions      List of udev events which should trigger and action
                    Valid actions are: 'add', 'remove', 'change', 'online', 'offline'. Defaults to 'add, change, online'
--filters           List of comma separated udev monitor filters. Filters are applied with OR logic. Example:
                    'usb,tty'
--action            Path to script. Script will get detected device as only argument.
--timeout           Maximum execution time for script
--config            Optional path to config file

Optional configuration file layout

[UDEV_MONITOR]
devices = '0665:5161'
filters = 'usb'
action = '/path/to/script.sh'
udev_events = 'add'
timeout = 3600

Setting monitor up as a service

• copy file scripts/udev_monitor@.service to /etc/systemd/system
• Reload daemons
• Create configuration file in /etc/udev_monitor from example config in scripts/udev_monitor.conf.example
• Launch service

Example:

cp scripts/udev_monitor\@.service to /etc/systemd/system
systemctl daemon-reload

mkdir /etc/udev_monitor
cat << EOF > /etc/udev_monitor/udev_monitor1.conf
devices = '0665:5161'
filters = 'usb'
action = '/path/to/script.sh'
udev_events = 'add'
timeout = 3600
EOF

systemctl enable --now udev_monitor@udev_monitor1.conf

You can launch multiple udev_monitor instances by creating multiple conf files and loading them with:

systemctl enable --now udev_monitor@umy_ups.conf
systemctl enable --now udev_monitor@my_modem.conf
systemctl enable --now udev_monitor@my_harddrive.conf

Further examples

Automatically attach an USB device (4G modem) to a KVM virtual machine with libvirt and udev_monitor

Let's imagine we have a Sierra 4G model that identifies as 1199:9097, and we would like to attach it to VM modem.vm.local

Grab yourself a copy of usb_reset via pip install usb_reset

Create the following script as /usr/local/bin/attach_modem.sh and make it executable with chmod +x /usr/local/bin/attach_modem.sh

#!/usr/bin/env bash

# /usr/local/bin/usb_reset.py --reset-device --device 1199:9071

virsh detach-device sms.badmin.local /root/4G_modem.xml
virsh attach-device sms.badmin.local /root/4G_modem.xml

Create the file /root/4G_modem.xml containing:

    <hostdev mode='subsystem' type='usb' managed='yes'>
      <source>
        <vendor id='0x1199'/>
        <product id='0x9071'/>
      </source>
    </hostdev>

Now we must execute that script everytime the USB 4G modem is plugged-in, so we get to re-attach it to the VM.

In order to do so, let's create the following conf file in /etc/udev_monitor/modem.conf

[UDEV_MONITOR]
devices = 1199:9071
filters = usb
action = /usr/local/bin/attach_modem.sh
udev_events = add
timeout = 300

Now let's create a systemd service by copying udev_monitor@.service from this git repo to /etc/systemd/system

Once this is done, we just can activate the service with systemctl enable --now udev_monitor@modem.conf

Reset a lawless UPS USB

Some of the USB uninterrupted power supplies (smaller devices) have a quite unreliable USB/Serial interface. Sometimes it's needed to restart the usb port for the device to work properly.

In that case, we can use udev_monitor to trigger a usb reset on device plug-in.