Kernel parameters aside (console=ttyUSB0 console=tty0), I am trying to get a login console working on a USB-to-serial adapter.

systemctl enable serial-getty@ttyUSB0.service systemctl start serial-getty@ttyUSB0.service

This works without issue on Debian 8. However when running the same on CentOS 7, my logs are filled with:

May 16 12:44:58 localhost.localdomain systemd[1]: Starting Serial Getty on ttyUSB0… May 16 12:44:58 localhost.localdomain agetty[1842]: /dev/ttyUSB0: cannot open as standard input: Permission denied May 16 12:45:08 localhost.localdomain systemd[1]:
serial-getty@ttyUSB0.service holdoff time over, scheduling restart. May 16 12:45:08 localhost.localdomain systemd[1]: Started Serial Getty on ttyUSB0. May 16 12:45:08 localhost.localdomain systemd[1]: Starting Serial Getty on ttyUSB0… May 16 12:45:08 localhost.localdomain agetty[1845]: /dev/ttyUSB0: cannot open as standard input: Permission denied May 16 12:45:18 localhost.localdomain systemd[1]:
serial-getty@ttyUSB0.service holdoff time over, scheduling restart. May 16 12:45:18 localhost.localdomain systemd[1]: Started Serial Getty on ttyUSB0. May 16 12:45:18 localhost.localdomain systemd[1]: Starting Serial Getty on ttyUSB0… May 16 12:45:18 localhost.localdomain agetty[1850]: /dev/ttyUSB0: cannot open as standard input: Permission denied May 16 12:45:29 localhost.localdomain systemd[1]:
serial-getty@ttyUSB0.service holdoff time over, scheduling restart. May 16 12:45:29 localhost.localdomain systemd[1]: Started Serial Getty on ttyUSB0. May 16 12:45:29 localhost.localdomain systemd[1]: Starting Serial Getty on ttyUSB0… May 16 12:45:29 localhost.localdomain agetty[1853]: /dev/ttyUSB0: cannot open as standard input: Permission denied May 16 12:45:39 localhost.localdomain systemd[1]:
serial-getty@ttyUSB0.service holdoff time over, scheduling restart. May 16 12:45:39 localhost.localdomain systemd[1]: Started Serial Getty on ttyUSB0.

I thought this might be a permissions issue. But comparing the permission on the debian box to the CentOS box yeilds the same results. When no one is logged in on the serial line on both machines, the permissions on the device node are as follows:

crw–w—-. 1 root tty 188, 0 May 16 13:49 /dev/ttyUSB0
(root:tty 0640)

Any ideas as to what is blocking the serial login on the CentOS 7 box?