问题
I write systemd services that launch with root privileges and de-privilege themselves to a system account (called mxdaemon). These services require access to the physical serial port (/dev/ttyS0) on the PC. Serial port ls -l:
Serial port: crw-rw---- 1 root dialout 4, 64 Jun 13 22:00 /dev/ttyS0
When run as root, the service has no problem communicating via the serial port.
When the service is configured to de-privilege to mxdaemon, I get a permission denied error when attempting to access /dev/ttyS0.
mxdaemon is a member of both the dialout & tty groups:
mxdaemon : mxdaemon dialout tty
Even after logging out and/or rebooting the PC, I still get permission denied for ANY user besides root.
Hours of scouring the Internet suggest that everything is configured correctly.
Any help would be appreciated!
-Rob
@sawdust: Thanks for the reply! Here's the info...
/etc/group : dialout:x:20:mxdaemon,mxadmin
/etc/gshadow : dialout:*::mxdaemon,mxadmin
Thanks for the pointer @sawdust - here's what the command yielded...
ps -o user= -o group= -p 15150
mxdaemon root
So, the user is mxdaemon but it shows being part of the root group?
来源：https://stackoverflow.com/questions/50858443/serial-port-permission-denied-for-non-root-user-with-dialout-group-privileges-ev