Hotplug -- Legacy
 | See the Hotplug article for information on the current approach. The “hotplug2” daemon was removed in 2013 (r36987) and replaced with procd. |
Hotplug2 was a trivial replacement of some of the UDev functionality in a tiny pack, intended for Linux early userspace: Init RAM FS and InitRD. Hotplug executes scripts located in the respective hotplug directory: /etc/hotplug.d/ on certain events, like when an interface goes up or down or when a button gets pressed.
It can be very useful with PPPoE-connection or in an unstable network. Hotplug has been available since OpenWrt 'Kamikaze' 7.06 and was removed in 2013, prior to the release of “Attitude Adjustment”.
It is also used by hardware.button
What is hotplug?
Best answer to this question is found on Chris Lumens's website.
How it works
Every time an interface goes up or down, all scripts in the /etc/hotplug.d/iface/ directory are executed, in alphabetical order. According to an informal convention a numeric prefix is added to each script name to set the correct order of running. That's why the scripts there are named like this:
/etc/hotplug.d/iface/<nn>-<scriptname> e.g.: 10-routes, 20-firewall
Kernel module: button-hotplug
Configuration
Modify /etc/hotplug2.rules to enable Hotplug execute your script(s) in /etc/hotplug.d/<type>. <type> is a kind of hotplug device; such as usb. In /etc/hotplug2.rules, remove '^' before <type> which can be net, input, button, usb etc.
$include /etc/hotplug2-common.rules
SUBSYSTEM ~~ (^net$|^input$|^button$|^usb$|^ieee1394$|^block$|^atm$|^zaptel$|^tty$) {
exec /sbin/hotplug-call %SUBSYSTEM%
}
DEVICENAME == watchdog {
exec /sbin/watchdog -t 5 /dev/watchdog
next-event
}
Simply place your script(s) into the respective hotplug subdirectory. Script looks like this:
There are three main environment variables that are passed to each iface hotplug-script:
| Variable name | Description |
|---|---|
| ACTION | Either “ifup” or “ifdown” |
| INTERFACE | Name of the interface which went up or down (e.g. “wan” or “ppp0”) |
| DEVICE | Physical device name which interface went up or down (e.g. “eth0.1” or “br-lan”) |
Examples
Save the example script at /etc/hotplug.d/iface/99-my-action.
#!/bin/sh
[ “$ACTION” = ifup ] && {
logger -t button-hotplug Device: $DEVICE / Action: $ACTION
} |
Every time an interface goes up then the if/fi statement will be executed.
→ hardware.button makes ample use of hotplug.
Niii has posted this quick example for a USB WiFi device hotplug event to trigger an init.d network restart wlan0 script.
For determine RTL8188SU_PRODID variable, use “lsusb -v”:
idVendor 0x0bda Realtek Semiconductor Corp. idProduct 0x8171 RTL8188SU 802.11n WLAN Adapter bcdDevice 2.00
/etc/hotplug.d/usb/20-rtl8188su
#!/bin/sh
BINARY=“/sbin/wifi up”
RTL8188SU_PRODID=“bda/8171/200”
if [ “${PRODUCT}” = “${RTL8188SU_PRODID}” ]; then
if [ “${ACTION}” = “add” ]; then
${BINARY}
fi
fi |
/etc/hotplug.d/usb/20-cp210x
An other script to create a symlink instead of renaming the device.
I test if DEVICE_NAME is empty because when I plug usb device I retrieve two add event, and the first come before created device, so symlink fails.
#!/bin/sh
CP210_PRODID=“10c4/ea60/100”
SYMLINK=“my_link”
if [ “${PRODUCT}” = “${CP210_PRODID}” ];
then if [ “${ACTION}” = “add” ];
then
DEVICE_NAME=$(ls /sys/$DEVPATH | grep tty)
if [ -z ${DEVICE_NAME} ];
then logger -t Hotplug Warning DEVICE_NAME is empty
exit
fi
logger -t Hotplug Device name of cp210 is $DEVICE_NAME
ln -s /dev/$DEVICE_NAME /dev/${SYMLINK}
logger -t Hotplug Symlink from /dev/$DEVICE_NAME to /dev/${SYMLINK} created
fi
fi
if [ “${PRODUCT}” = “${CP210_PRODID}” ];
then if [ “${ACTION}” = “remove” ];
then
rm /dev/${SYMLINK}
logger -t Hotplug Symlink /dev/${SYMLINK} removed
fi
fi |
Script that detects if plugged usb device is bluetooth or not.
#!/bin/sh
BT_PRODID=“a12/1/”
BT_PRODID_HOT=`echo $PRODUCT | cut -c 1-6`
#logger -t HOTPLUG “PRODUCT ID is” $BT_PRODID_HOT
if [ “$BT_PRODID_HOT” = “$BT_PRODID” ]; then
if [ “$ACTION” = “add” ]; then
logger -t HOTPLUG “bluetooth device has been plugged in!”
if [ “$BSBTID_NEW” = “$BSBTID_OLD” ]; then
logger -t HOTPLUG “bluetooth device hasn't changed”
else
logger -t HOTPLUG “bluetooth device has changed”
fi
fi
if [ “$ACTION” = “remove” ]; then
logger -t HOTPLUG “bluetooth device has been removed!”
fi
else
logger -t HOTPLUG “USB device is not bluetooth”
fi |
Auto start mjpg-streamer when an usb camera is plugged in.
Firstly, remove '^' before 'input' in /etc/hotplug2.rules to enable Hotplug execute script(s) in /etc/hotplug.d/input.
Secondly, add /etc/hotplug.d/input/30-mjpg-streamer
case "$ACTION" in
add)
# start process
/etc/init.d/mjpg-streamer start
;;
remove)
# stop process
/etc/init.d/mjpg-streamer stop
;;
esac
Coldplug
If you had notice the udev and eudev were removed in the openwrt 18.0.* release, don't be afraid because you still can make the things works.
Using hotplug scripts as coldplug
You just need to pay atention at the ACTION env var, at the boot are executed 'bind' actions.
So, just add this option to hotplug run accordinly. In my case I used this:
Take a look into file /etc/hotplug.d/usb/22-symlinks
#!/bin/sh
# Description: Action executed on boot (bind) and with the system on the fly
if [ "$ACTION" = 'bind' ] ; then
case "${PRODUCT}" in
1bc7*) # Telit HE910 3g modules product id prefix
DEVICE_NAME=$(ls /sys/$DEVPATH | grep tty)
DEVICE_TTY=$(ls /sys/$DEVPATH/tty/)
# Module Telit HE910-* connected to minipciexpress slot MAIN
if [ ${DEVICENAME} = '1-1.3:1.0' ] ; then
ln -s /dev/$DEVICE_TTY /dev/ttyMODULO1_DIAL
logger -t Hotplug Symlink from /dev/$DEVICE_TTY to /dev/ttyMODULO1_DIAL created
elif [ ${DEVICENAME} = '1-1.3:1.6' ] ; then
ln -s /dev/$DEVICE_TTY /dev/ttyMODULO1_DATA
logger -t Hotplug Symlink from /dev/$DEVICE_TTY to /dev/ttyMODULO1_DATA created
# Module Telit HE910-* connected to minipciexpress slot SECONDARY
elif [ ${DEVICENAME} = '1-1.2:1.0' ] ; then
ln -s /dev/$DEVICE_TTY /dev/ttyMODULO2_DIAL
logger -t Hotplug Symlink from /dev/$DEVICE_TTY to /dev/ttyMODULO2_DIAL created
elif [ ${DEVICENAME} = '1-1.2:1.6' ] ; then
ln -s /dev/$DEVICE_TTY /dev/ttyMODULO2_DATA
logger -t Hotplug Symlink from /dev/$DEVICE_TTY to /dev/ttyMODULO2_DATA created
fi
;;
esac
fi
# Action to remove the symlinks
if [ "$ACTION" = 'remove' ] ; then
case "${PRODUCT}" in
1bc7*) # Telit HE910 3g modules product id prefix
# Module Telit HE910-* connected to minipciexpress slot MAIN
if [ ${DEVICENAME} = '1-1.3:1.0' ] ; then
rm /dev/ttyMODULO1_DIAL
logger -t Hotplug Symlink /dev/ttyMODULO1_DIAL removed
elif [ ${DEVICENAME} = '1-1.3:1.6' ] ; then
rm /dev/ttyMODULO1_DATA
logger -t Hotplug Symlink /dev/ttyMODULO1_DATA removed
# Module Telit HE910-* connected to minipciexpress slot SECONDARY
elif [ ${DEVICENAME} = '1-1.2:1.0' ] ; then
rm /dev/ttyMODULO2_DIAL
logger -t Hotplug Symlink /dev/ttyMODULO2_DIAL removed
elif [ ${DEVICENAME} = '1-1.2:1.6' ] ; then
rm /dev/ttyMODULO2_DATA
logger -t Hotplug Symlink /dev/ttyMODULO2_DATA removed
fi
;;
esac
fi
Logs generated by Coldplug script below
root@OpenWrt:~#logread | grep Hotplug Fri Sep 21 15:31:00 2018 user.notice Hotplug: Symlink from /dev/ttyACM0 to /dev/ttyMODULO2_DIAL created Fri Sep 21 15:31:06 2018 user.notice Hotplug: Symlink from /dev/ttyACM3 to /dev/ttyMODULO2_DATA created Fri Sep 21 15:31:39 2018 user.notice Hotplug: Symlink from /dev/ttyACM6 to /dev/ttyMODULO1_DIAL created Fri Sep 21 15:31:46 2018 user.notice Hotplug: Symlink from /dev/ttyACM9 to /dev/ttyMODULO1_DATA created Fri Sep 21 15:32:03 2018 user.notice Hotplug: Symlink /dev/ttyMODULO1_DIAL removed Fri Sep 21 15:32:10 2018 user.notice Hotplug: Symlink /dev/ttyMODULO1_DATA removed Fri Sep 21 15:33:17 2018 user.notice Hotplug: Symlink /dev/ttyMODULO2_DIAL removed Fri Sep 21 15:33:24 2018 user.notice Hotplug: Symlink /dev/ttyMODULO2_DATA removed root@OpenWrt:~#
Troubleshoot
If you wish to troubleshoot hotplug of some type of device this can be done via simple debug script. For example to troubleshoot adding and removing of any type of usb devices, simply create this /etc/hotplug.d/usb/10-usb_debug script with all variables:
#!/bin/sh logger -t DEBUG "hotplug usb: action='$ACTION' devicename='$DEVICENAME' devname='$DEVNAME' devpath='$DEVPATH' product='$PRODUCT' type='$TYPE' interface='$INTERFACE'"
or this one with only essential ones used:
#!/bin/sh logger -t DEBUG "hotplug usb: action='$ACTION' product='$PRODUCT' type='$TYPE' interface='$INTERFACE'"
So with debuging enabled here is how it looks like when you plug two different usb bluetooth dongles:
action='add' product='a12/1/1915' type='224/1/1' interface='' action='add' product='a12/1/1915' type='224/1/1' interface='224/1/1' action='add' product='a12/1/1915' type='224/1/1' interface='224/1/1' action='add' product='a12/1/1915' type='224/1/1' interface='254/1/0' action='remove' product='a12/1/1915' type='224/1/1' interface='224/1/1' action='remove' product='a12/1/1915' type='224/1/1' interface='224/1/1' action='remove' product='a12/1/1915' type='224/1/1' interface='254/1/0' action='remove' product='a12/1/1915' type='224/1/1' interface='' action='add' product='a12/1/134' type='224/1/1' interface='' action='add' product='a12/1/134' type='224/1/1' interface='224/1/1' action='add' product='a12/1/134' type='224/1/1' interface='224/1/1'
So my using some (maybe flawed) logic we can deduce that match bluetooth is possible if we use product='a12/1*'