How can I have launchd execute a script when a certain kind of usb device is connected?

Question

MrLinear OP

Created Sep ’18

Replies 6

Boosts 0

Views 3.7k

Participants 4

I need launchd to execute a script when a certain kind of usb device is connected. Specifically, an iOS device.

is this possible? If so, what should the launchd plist look like?

Answered by DTS Engineer in 332600022

Any idea on what I am doing wrong?

Failing to understand the

launchd

executable model )-:

I like to say that

launchd

is level triggered? It will keep the job running as long as the conditions expressed in the job’s property list are true. Consider the classic networking scenario:

The job declares that it wants to listen on a specific port.
Starting with the job stopped…
Someone connects to the port.
```
launchd
```
starts the job.
The job accepts the connection from the socket and runs it.
The job keeps doing this until it exits for some reason (typically an idle exit or a memory pressure exit).

Imagine, however, if the job crashes before accepting the connection (this it, at the start of step 5). The connection is still pending on the socket, and thus

launchd

starts the job again. And it will keep doing this until the job handles all the connections.

This is a good thing in general.

In your case the conditions for starting the job are the presence of a particular USB peripheral. That peripheral doesn’t go away when you finish talking to it, and thus

launchd

keeps you running.

What you’re supposed to do here is as follows:

When you’re launched, use
```
xpc_set_event_stream_handler
```
to listen for match events coming in from the system.
When you get one, use the
```
IOMatchLaunchServiceID
```
property to find the corresponding I/O Registry entry.
Run that entry.
It seems like in your case you don’t actually want to do anything with the entry, so this step boils down to:
- Log the entry.
- Ignore it.
On the other hand, if you also want to log disconnects running the entry is a little more complex.
Either opt in to memory pressure exits (
```
EnablePressuredExit
```
), or implement an idle exit, or just let your job run continuously.

Share and Enjoy
—
Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware

let myEmail = "eskimo" + "1" + "@apple.com"

Boost

Answer 1

KMT OP

Sep ’18

Which version(s) macOS does your app support?

0

Answer 2

DTS Engineer OP

Apple

Sep ’18

You should look to the

LaunchEvents

>

com.apple.iokit.matching

property. You can use that tell

launchd

to start your job when a specific I/O Kit service is discovered. See the

launchd.plist

and

xpc_set_event_stream_handler

man pages for details.

Share and Enjoy
—
Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware

let myEmail = "eskimo" + "1" + "@apple.com"

0

Answer 3

MrLinear OP

Sep ’18

I tried the following plist, but it is not working as expected.

After I bootstrap the job, I can connect a device and my test_connect.py script will be executed and connect_log.log will be appended to.

However, Launchd keeps spawning the job every 10 seconds. Even if I disconnect the device, launchd will spawn it every 10 seconds and connect_log.log will be appended to.

Any idea on what I am doing wrong?

idProduct: 4776 = 0x12a8

idVendor: 1452 = 0x05ac

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">

<dict>

<key>Label</key>

<string>org.myorg.device_connect</string>

<key>RunAtLoad</key>

<key>KeepAlive</key>

<key>WorkingDirectory</key>

<string>/Users/ericg/Desktop/test_connect</string>

<key>ProgramArguments</key>

<array>

<string>/usr/local/Cellar/python/3.7.0/Frameworks/Python.framework/Versions/3.7/Resources/Python.app/Contents/MacOS/Python</string>

<string>/Users/ericg/Desktop/test_connect/test_connect.py</string>

</array>

<key>LaunchEvents</key>

<dict>

<key>com.apple.iokit.matching</key>

<dict>

<key>com.apple.device-attach</key>

<dict>

<key>idProduct</key>

<key>idVendor</key>

<key>IOProviderClass</key>

<string>IOUSBDevice</string>

<key>IOMatchLaunchStream</key>

<true/>

</dict>

</plist>

The test_connect.py script looks like:

import os

import datetime

SCRIPT_PATH = os.path.dirname( __file__ )

logfile = os.path.join( SCRIPT_PATH, "connect_log.log" )

currentTime = datetime.datetime.now().strftime("%I:%M%p on %B %d, %Y")

with open( logfile, "a" ) as fp:

fp.write( currentTime + "\n" )

0

Answer 4

DTS Engineer OP

Apple

Sep ’18

Accepted Answer

Any idea on what I am doing wrong?

Failing to understand the

launchd

executable model )-:

I like to say that

launchd

is level triggered? It will keep the job running as long as the conditions expressed in the job’s property list are true. Consider the classic networking scenario:

The job declares that it wants to listen on a specific port.
Starting with the job stopped…
Someone connects to the port.
```
launchd
```
starts the job.
The job accepts the connection from the socket and runs it.
The job keeps doing this until it exits for some reason (typically an idle exit or a memory pressure exit).

Imagine, however, if the job crashes before accepting the connection (this it, at the start of step 5). The connection is still pending on the socket, and thus

launchd

starts the job again. And it will keep doing this until the job handles all the connections.

This is a good thing in general.

In your case the conditions for starting the job are the presence of a particular USB peripheral. That peripheral doesn’t go away when you finish talking to it, and thus

launchd

keeps you running.

What you’re supposed to do here is as follows:

When you’re launched, use
```
xpc_set_event_stream_handler
```
to listen for match events coming in from the system.
When you get one, use the
```
IOMatchLaunchServiceID
```
property to find the corresponding I/O Registry entry.
Run that entry.
It seems like in your case you don’t actually want to do anything with the entry, so this step boils down to:
- Log the entry.
- Ignore it.
On the other hand, if you also want to log disconnects running the entry is a little more complex.
Either opt in to memory pressure exits (
```
EnablePressuredExit
```
), or implement an idle exit, or just let your job run continuously.

Share and Enjoy
—
Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware

let myEmail = "eskimo" + "1" + "@apple.com"

0

Answer 5

MrLinear OP

Sep ’18

Thanks. With that understanding, I believe I have the problem solved.

I found this handy little python package:

https://github.com/prezesp/py-iokit-matching-handler

which consumes the com.apple.iokit.matching event and ignores it.

With this package available, I can simply add

from PyIOKitMatchingHandler import IOKitMatchingHandler

# Consume an event

handler = IOKitMatchingHandler()

handler.handle()

and my script is called only once as it should be.

I don't care about detecting disconnects, only connects.

0

Answer 6

lsrggr OP

May ’23

You may consider Stecker also. It is a free utility that triggers shortcuts on device attachment and detachment.

0