The 3270 is the classic 'green-screen' console of the mainframes (see the IBM 3270 Wikipedia article).
The 3270 data stream is not implemented within QEMU; the device only provides TN3270 (a telnet extension; see RFC 854 and RFC 1576) and leaves the heavy lifting to an external 3270 terminal emulator (such as x3270
) to make a single 3270 device available to a guest. Note that this supports basic features only.
To provide a 3270 device to a guest, create a x-terminal3270
linked to a tn3270
chardev. The guest will see a 3270 channel device. In order to actually be able to use it, attach the x3270
emulator to the chardev.
- Make sure that 3270 support is enabled in the guest's Linux kernel. You need
CONFIG_TN3270
and at least one ofCONFIG_TN3270_TTY
(for additional ttys) orCONFIG_TN3270_CONSOLE
(for a 3270 console). Add a
tn3270
chardev and ax-terminal3270
to the QEMU command line:-chardev socket,id=ch0,host=0.0.0.0,port=2300,wait=off,server=on,tn3270=on -device x-terminal3270,chardev=ch0,devno=fe.0.000a,id=terminal0
- Start the guest. In the guest, use
chccwdev -e 0.0.000a
to enable the device. On the host, start the
x3270
emulator:x3270 <host>:2300
In the guest, locate the 3270 device node under
/dev/3270/
(say,tty1
) and start a getty on it:systemctl start serial-getty@3270-tty1.service
This should get you an additional tty for logging into the guest.
- If you want to use the 3270 device as the Linux kernel console instead of an additional tty, you can also append
conmode=3270 condev=000a
to the guest's kernel command line. The kernel then should use the 3270 as console after the next boot.
3270 support is very basic. In particular:
- Only one 3270 device is supported.
- It has only been tested with Linux guests and the x3270 emulator.
- TLS/SSL is not supported.
- Resizing on reattach is not supported.
- Multiple commands in one inbound buffer (for example, when the reset key is pressed while the network is slow) are not supported.