No I did not see any DENIED entries.
But I did notice this on the linux command line, which may interfere with the usage of the serial port (other then console). Utilities like getty running on ttyS0.
Not sure yet ?
Jan 24 15:53:38 localhost kernel: Kernel command line: 8250.nr_uarts=1 cma=256M bcm2708_fb.fbwidth=1824 bcm2708_fb.fbheight=984 bcm2708_fb.fbswap=1 vc_mem.mem_base=0x3ec00000 vc_mem.mem_size=0x40000000 dwc_otg.lpm_enable=0 console=ttyS0,115200 elevator=deadline rng_core.default_quality=700 vt.handoff=2 quiet splash root=/dev/disk/by-label/writable net.ifnames=0 init=/lib/systemd/systemd ro panic=-1 fixrtc snap_core=core18_1654.snap snap_kernel=pi-kernel_69.snap
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Jan 24 15:53:38 localhost kernel: Serial: 8250/16550 driver, 1 ports, IRQ sharing enabled
Jan 24 15:53:38 localhost kernel: console [ttyS0] disabled
Jan 24 15:53:38 localhost kernel: 3f215040.serial: ttyS0 at MMIO 0x0 (irq = 166, base_baud = 31250000) is a 16550
Jan 24 15:53:38 localhost kernel: console [ttyS0] enabled
Jan 24 15:53:39 localhost systemd[1]: Found device /dev/ttyS0.
Jan 24 16:02:44 localhost sudo[844]: amodster : TTY=pts/0 ; PWD=/home/amodster ; USER=root ; COMMAND=/home/amodster/myserial.py
Jan 24 16:02:44 localhost sudo[844]: pam_unix(sudo:session): session opened for user root by amodster(uid=0)
Jan 24 16:02:45 localhost sudo[844]: pam_unix(sudo:session): session closed for user root
Jan 24 16:02:45 localhost systemd[1]: Started Serial Getty on ttyS0.
Jan 24 16:02:45 localhost systemd[1]: serial-console-conf@ttyS0.service: Service has no hold-off time, scheduling restart.
Jan 24 16:02:45 localhost systemd[1]: serial-console-conf@ttyS0.service: Scheduled restart job, restart counter is at 1.
Jan 24 16:02:45 localhost systemd[1]: Stopped Ubuntu Core Firstboot Configuration ttyS0.
Jan 24 16:02:45 localhost systemd[1]: Started Ubuntu Core Firstboot Configuration ttyS0.
Jan 24 16:02:45 localhost systemd[1]: Stopping Serial Getty on ttyS0…
Jan 24 16:02:45 localhost systemd[1]: Stopped Serial Getty on ttyS0.
Note: systemd tries to stop Getty, but it does not clean up in time.
Is there a way to stop this service ?
amodster@localhost:~$ systemctl status serial-console-conf@ttyS0.service
● serial-console-conf@ttyS0.service - Ubuntu Core Firstboot Configuration ttyS0
Loaded: loaded (/lib/systemd/system/serial-console-conf@.service; static; vendor preset: enabled)
Active: active (running) since Sat 2020-01-25 04:26:36 UTC; 50min ago
Process: 1378 ExecStopPost=/bin/systemctl start serial-getty@ttyS0 (code=exited, status=0/SUCCESS)
Process: 1380 ExecStartPre=/bin/systemctl stop serial-getty@ttyS0 (code=exited, status=0/SUCCESS)
Main PID: 1382 (console-conf-wr)
Tasks: 1 (limit: 1588)
CGroup: /system.slice/system-serial\x2dconsole\x2dconf.slice/serial-console-conf@ttyS0.service
└─1382 /bin/bash /usr/share/subiquity/console-conf-wrapper --serial
amodster@localhost:~$ systemctl status serial-getty@ttyS0
● serial-getty@ttyS0.service - Serial Getty on ttyS0
Loaded: loaded (/lib/systemd/system/serial-getty@.service; indirect; vendor preset: enabled)
Drop-In: /lib/systemd/system/serial-getty@.service.d
└─console-conf-serial.conf
Active: inactive (dead) since Sat 2020-01-25 04:26:36 UTC; 51min ago
Docs: man:agetty(8)
man:systemd-getty-generator(8)
http://0pointer.de/blog/projects/serial-console.html
Process: 1381 ExecStart=/sbin/agetty -o -p – \u --keep-baud 115200,38400,9600 ttyS0 $TERM (code=killed, signal=TERM)
Process: 1379 ExecStartPre=/bin/systemctl start serial-console-conf@ttyS0.service (code=exited, status=0/SUCCESS)
Main PID: 1381 (code=killed, signal=TERM)