Servlet requires nonprivileged access. Tomcat was added to gpio group and udev rules applied. But after kernel update to Linux pihive1 6.1.61+ #1696 Thu Nov 2 16:33:31 GMT 2023 armv6l GNU/Linux on
Raspberry Pi Details:
Type: Pi Zero-W, Revision: 01, Memory: 512MB, Maker: Sony
* Device tree is enabled.
*--> Raspberry Pi Zero W Rev 1.1
* This Raspberry Pi supports user-level GPIO access.
servlet reports exception:
Nov 17 14:17:57 pihive1 tomcat9[484]: java.lang.RuntimeException: Unable to open GPIO direction interface for pin [22]: Permission denied
Nov 17 14:17:57 pihive1 tomcat9[484]: at com.pi4j.wiringpi.GpioUtil.export(Native Method)
Nov 17 14:17:57 pihive1 tomcat9[484]: at com.pi4j.io.gpio.WiringPiGpioProviderBase.export(WiringPiGpioProviderBase.java:108)
Adapting /etc/udev/rules.d/99-com.rule by adding /dev/gpiomem
$ diff backup-99-com.rules /etc/udev/rules.d/99-com.rules
10c10,11
< chown -R root:gpio /sys$devpath && chmod -R 770 /sys$devpath\
---
> chown -R root:gpio /sys$devpath && chmod -R 770 /sys$devpath;\
> chown root:gpio /dev/gpiomem && chmod g+rw /dev/gpiomem\
solved the problem, but assumption was that pi4j uses same deprecated sysfs approach as python gpio lib. Did I miss something?
Note: the "first try fails" - topic mentioned in Raspberry pi GPIO sysfs, fopen: Permission denied persists but is acceptable.