/dev/rtc not readable with CAP_SYS_RESOURCE capability
 

I need to run the ntpd without root privileges, which should be possible via libcap support which is available for the ntpd.

But I have a private ntpd reference clock driver for the realtime clock (/dev/rtc) as a reference source. When reading the RTC clock time under non-root account, the open("/dev/rtc",O_RDONLY) fails with error 13: Permission denied. I have read here http://linux.die.net/man/4/rtc that the capability permission of CAP_SYS_RESOURCE should allow that. But it doesn't. My ntpd process permissions are "cap_net_bind_service,cap_sys_resource,cap_sys_time+ei".

Is there any way to read the /dev/rtc under non-root account?