Re: [arch-general] udev rules 2 times exec script

   If the command shares any resources, and name “autobackup” suggests 
it does, it should include some mechanism that prevents concurrent 
execution if another instance is already running. Otherwise, even if a 
single match happens, multiple instances of the script may be executed. 
For USB devices that may be a tiny power interruption during insertion, 
causing it to be detected, removed, detected again:

insertion - - - removal - - - insertion - - - - - - -
   |-- script ---------------------------------------> \_ two instances
                                 |-- script ---------> /  of the code

It should be either of those:
   |-- script ------------------------------------------------->
                                 |--- BAIL OUT! -|
or
   |-- script --------------------------------- end|
                                 |-- WAIT .......... script --->

> SUBSYSTEM=="block", ACTION=="add", ATTRS{idVendor}=="058f",
> ATTRS{idProduct}=="6387", SYMLINK+="external%n",
> RUN+="/usr/local/bin/autobackup.sh"
> 
> This works well, buth exec 2 times the script...
> 
> Jun 12 13:53:09 archlaptop autobackup.sh: BEGIN SCRIPT
> Jun 12 13:53:13 archlaptop autobackup.sh: BEGIN SCRIPT
   Because there are two matches for that pattern:
  - //devices/platform/…/target0:0:0/0:0:0:0/block/sda
  - //devices/platform/…/target0:0:0/0:0:0:0/block/sda/sda1
Both of them have SUBSYSTEM=="block", ACTION=="add", 
ATTRS{idVendor}=="058f" and ATTRS{idProduct}=="6387".

> If add ENV{DEVTYPE}=="usb_device" and change the
> SUBSYSTEM=="usb_device" , when plug usb, udev does nothing ...
   Because there is nothing that matches SUBSYSTEM=="usb_device".