Via a serial connection, and either a pair of modems or a "null modem" cable, one system can act as a terminal for another system. This is variously known as "call out" or "dial up". This package contains tools for emulating a real terminal on another system via a "call out" serial port when the "null modem" case applies.
Call-out is done with ttycallout@device services, configured to use those devices.
Such a call-out service is a very simple service, which can be managed just like other ordinary services, started and stopped and enabled and disabled in the usual way.
The service runs console-terminal-emulator to provide terminal emulation, attached to the "call out" serial device /dev/device and presenting itself as the /run/dev/device user-space virtual terminal.
This is just another user-space virtual terminal that can be realized and multiplexed like any others.
So (for example) one could run a bank of such ttycallout@cuauN services under a multiplexor and an input method; configure them with specific dedicated HIDs and framebuffers; and use individualized keyboard maps and fonts.
These services are suitable for serial ports connected via "null modem" cables; they have no modem command functionality.
It is assumed that the cable is always connected, and the speed/parity/bits are pre-configured by the machines at both ends of the connection.
Since console-terminal-emulator provides a fixed known terminal emulation, the system at the other end of the connection must be told the appropriate TERM environment variable for the terminal type.
run scripts look like
The run script for such services is basically this (using ttycallout@cuau1 as an example):
#!/bin/nosh setenv TTY /dev/cuau1 setsid open-controlling-terminal --revoke setuidgid --primary-group user-vt-realizer -- user-vt-emulator console-terminal-emulator /run/dev/cuau1
The services are ttycallout@cuau0 through to ttycallout@cuauf, matching the operating system's real terminal devices /dev/cuau0 to /dev/cuauf.
These should not be run at the same time as the matching getty@ttyu0 through to getty@ttyuf service(s).
The services are ttycallout@tty00 through to ttycallout@tty07 and ttycallout@ttyU0 through to ttycallout@ttyU3, matching the operating system's real terminal devices /dev/tty00 to /dev/tty07 and /dev/ttyU0 to /dev/ttyU3.
These should not be run at the same time as the matching getty@tty00 through to getty@tty07 and getty@ttyU0 through to getty@ttyU3 service(s).
The services are ttycallout@ttyS0 through to ttycallout@ttyS3, matching the operating system's real terminal devices /dev/ttyS0 to /dev/ttyS3.
These should not be run at the same time as the matching agetty@ttyS0/mgetty@ttyS0 through to agetty@ttyS3/mgetty@ttyS3 service(s).