Run a udev rule for a USB flash drive when the computer is started with the device inserted

Question

I want my Ubuntu 15.04 x64 server system to execute a script whenever a certain flash drive is inserted. So I created a custom rule file with the following content

ACTION=="add",SUBSYSTEM=="usb",ATTR{idVendor}=="my-vendor",ATTR{idProduct}=="my-id",RUN+="/var/scripts/my-script.sh"

The script executed whenever the flash drive is inserted, but I have two problems with it:

1) The script is apparently not executed when the computer is (re-)started with the drive already inserted. Is there any way to execute the script after startup if the flash drive is already connected?

2) The script wants to mount the device, but If I try to mount the device like

mount LABEL=mylabel /some/path

or

mount UUID=my-uuid /some/path

The source cannot be found. Currently I inserted a

sleep 5s

into my script, but this does not seem like a reliable solution. Is there any (failure tolerant) way to wait for the system to be sufficiently initialized?

For testing purposes, the script only contained

#!/bin/sh
date >> /tmp/test.log

Answer 1

Rules for add actions are executed during system startup if the device is present. This is done by running udevadm info --action=add on a SysVinit system, and internally on an Upstart or Systemd system. However this happens very early in the boot process, at a time when the root filesystem is still mounted read-only and filesystems from /etc/fstab are not mounted yet. I'm not sure if /run is already available at that point. That may well be too early for what your script needs to do.

The quick-and-dirty but portable way to run your script during startup would be to run it from /etc/rc.local, conditionally on the device being present.

if [ -e /dev/disk/by-id/… ]; then
  /var/scripts/my-script.sh
fi

Beware that there's a possible race condition if the device is inserted during startup: the script will be executed as soon as the device detected, and then again from /etc/rc.local.

A cleaner solution would be to define a systemd unit and declare the dependencies that you need in your script. You still need to beware of the potential race condition.