Serial Port/UART cannot be used

[GhostGambler]

I want to use the UART functionality to communicate with the VM (in this example Linux) from macOS.

As configuration I used --uart2 0x2f8 3 and --uartmode2 file /tmp/serial_port2.

The Linux guest says everything is fine:

$ dmesg | grep tty
[    0.000000] Command line: BOOT_IMAGE=/boot/vmlinuz-4.15.0-23-generic root=LABEL=cloudimg-rootfs ro console=tty1 console=ttyS0
[    0.000000] Kernel command line: BOOT_IMAGE=/boot/vmlinuz-4.15.0-23-generic root=LABEL=cloudimg-rootfs ro console=tty1 console=ttyS0
[    0.004000] console [tty1] enabled
[    0.004000] console [ttyS0] enabled
[    1.535605] 00:02: ttyS0 at I/O 0x3f8 (irq = 4, base_baud = 115200) is a 16550A
[    1.721594] 00:03: ttyS1 at I/O 0x2f8 (irq = 3, base_baud = 115200) is a 16550A

The file /tmp/serial_port2 is created on the macOS file system, but when I want to access it with cat or screen, nothing happens. The commands just exit immediately:

$ screen /tmp/serial_port2 115200
[screen is terminating]
$ cat serial_port2 
$ 

If I run the command as root, screen starts and shows the message

Cannot exec 'serial_port2': No such file or directory  

If I instead use --uartmode2 tcpserver 8081, I can use nc 127.0.0.1 8081 and I receive data from the VM as expected.

I also created another VM with uartmode=client, but they also cannot communicate with each other.

Is this function not working, or am I doing something wrong?

[GhostGambler]

machine log

[janitor]

What do you expect to happen? file means output is written to an ordinary file. Have you read the manual?

[janitor]

You can also check #11011 for one way this can be done with screen.

[GhostGambler]

Oh, sorry, I did not mean file but server. I copied the wrong part of the configuration. (File works too.)

Btw. I just realized, that nc -U /tmp/serial_port2 works. But I still don't understand, why screen and cat do not work?

[GhostGambler]

Replying to janitor:

You can also check #11011 for one way this can be done with screen.

Ah, the other ticket helps I guess. I will take a closer look. Thanks!

[janitor]

Replying to GhostGambler:

Oh, sorry, I did not mean file but server. I copied the wrong part of the configuration. (File works too.)

Btw. I just realized, that nc -U /tmp/serial_port2 works. But I still don't understand, why screen and cat do not work?

screen doesn't support that kind of usage. Check "Window Types" section of the screen man page.