Documentation of usage for serial devices on synology disk stations (#…

…118)

* Documentation of usage for serial devices on synology disk stations

README.md

@@ -23,6 +23,42 @@ The second log `openHAB-start-stop.log` will be generated by starting and stoppi
 
 Installation und Prerequisite Install Java Documentation: [Official openHAB Usage Manual](http://docs.openhab.org/installation/synology.html)
 
+For usage of serial devices you need to check if openhab2 user has the appropriate rights to access the device in /dev and to create lock files in /run/lock
+To do so the installer tries to add the openhab2 user to the groups dialout and uucp. But these groups are not present on all synology diskstations.
+/run/lock for instance is created as this on a ds214play:
+drwxr-xr-x 5 root        root             160 Dec  9 20:11 lock
+and /dev/ttyUSB0 is per default also created for root only:
+crw------- 1 root root 188,  0 Dec  4 12:55 /dev/ttyUSB0
+The result in nrjavaserial / RXTX to access this port would be a no port found exception.
+
+To correct this you need three steps (login as admin on diskstations ssh login):
+a) create a group and assign openhab2 user to it
+ sudo synogroup --add uucp openhab2
+
+b) setup udev rule so that access rights in /dev/ are permanent and reload udev rules
+
+example for pl2303 usb to serial converter:
+ sudo echo 'SUBSYSTEM=="tty", ATTRS{idVendor}=="067b", ATTRS{idProduct}=="2303", GROUP="uucp", MODE="0660"' >>/usr/lib/udev/rules.d/50-yourrules
+
+example for general ttyUSB rule:
+ sudo echo 'KERNEL=="ttyUSB*", ACTION=="add", MODE="0660", GROUP="uucp"' >>/usr/lib/udev/rules.d/50-yourrules
+
+reload rules now:
+ sudo udevadm control --reload
+
+c) enable access for openhab2 user for lock file creation
+
+chmod 0775 /run/lock
+chown root.uucp /run/lock
+
+edit /etc/init/root-file-system.conf to persist this change.
+ sudo vi /etc/init/root-file-system.conf
+change line
+        /bin/mkdir -p /run/lock || true
+to
+        /bin/mkdir -m 0775 -p /run/lock || true
+        chown root.uucp /run/lock || true
+
 ## Forum
 
 Official community: [![Github Releases](https://img.shields.io/badge/openhab-forum-orange.svg)](https://community.openhab.org/t/synology-diskstation/1446)