udev/udevadm - dynamic dev symbolic link and proper access rights

Introduction

Thanks to the literature research of M.Traxler and the inventors of udev/udevadm it is possible to assign automatically (fixed) symbolic links for USB devices connected to the system pointing the current /dev entry point.

How To

Prerequisites

you have to have admin rights.

How to

• edit/create /etc/udev/rules.d/99-serial-permissions.rules
  
  • add the follwing line for general includes
    SUBSYSTEMS=="usb", ATTRS{idVendor}=="0403", SYMLINK+="$env{ID_SERIAL}", GROUP="users", MODE="0666"
    creates for every connected device of vendor id 0403 a symbolic link /dev/ to the connected device
    
  • for special devices those lines can be added in addition
    SUBSYSTEMS=="usb", ATTRS{idVendor}=="0403", ENV{ID_SERIAL}=="FTDI_FT232R_USB_UART_A100dQ2B", SYMLINK+="hadcon2", GROUP="users", MODE="0666"
SUBSYSTEMS=="usb", ATTRS{idVendor}=="0403", ENV{ID_SERIAL}=="FTDI_FT232R_USB_UART_A600801P", SYMLINK+="olimex", GROUP="users", MODE="0666"
    
  • for special devices (e.g. HadCon2) those lines can be added in addition
    • SUBSYSTEMS=="usb", ATTRS{idVendor}=="0403", ENV{ID_SERIAL}=="FTDI_FT232R_USB_UART_A100*", RUN+="/usr/bin/stty -F /dev/$kernel -opost -onlcr -isig -icanon -iexten -echo -echoe -echok -echoctl -echoke 115200 "
      
    • SUBSYSTEMS=="usb", ATTRS{idVendor}=="0403", ENV{ID_SERIAL}=="FTDI_FT232R_USB_UART_A801*", RUN+="/usr/bin/stty -F /dev/$kernel -opost -onlcr -isig -icanon -iexten -echo -echoe -echok -echoctl -echoke 115200 "
      
• to find out the IDs of connected systems
  udevadm info --export-db| grep FTDI| grep ID_SERIAL
  
  
• Finally reload rules and trigger a reconnect:
  
  udevadm control --reload-rules
udevadm trigger

Links

"Writing udev rules"

http://reactivated.net/writing_udev_rules.html

udev

https://wiki.ubuntuusers.de/udev/

"Tutorial on how to write basic udev rules in Linux"

https://linuxconfig.org/tutorial-on-how-to-write-basic-udev-rules-in-linux

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-- PeterZumbruch - 2019-03-22

This topic: Epics > WebHome > DevelopersCorner > TippsUsbDevDynamicDevSymLinkAndProperAccessRights
Topic revision: 2020-11-09, PeterZumbruch

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