Difference between the Terminals and Standard IO in runc and youki

Overview

youki's handling of process.terminal and stdio differs from runc in several ways. This is an umbrella issue to track the gaps.

Issues

• process.terminal field is ignored (#3522): youki does not read process.terminal from the OCI spec. PTY setup is driven solely by whether --console-socket is passed. runc validates the combination of terminal / detach / console-socket before starting the container.

• terminal=true + foreground (no --console-socket): no I/O bridge: When running a container with a TTY in foreground without a console socket, runc bridges the PTY master to the host stdio. youki has no equivalent — there is a // TODO: Handling when there isn't console-socket. comment acknowledging this gap. As a result, container output is not visible and host input is not forwarded.

• terminal=false + foreground: no explicit pipe setup: runc uses setupProcessPipes to connect the container's stdin/stdout/stderr to the host via explicit pipes. youki relies on implicit fd inheritance through fork, which accidentally works in simple cases but does not support I/O redirection via the API.

References

• runc checkTerminal / tty.go: https://github.com/opencontainers/runc/blob/main/tty.go
• runc setupProcessPipes: https://github.com/opencontainers/runc/blob/main/libcontainer/process_linux.go
• OCI Runtime Spec process.terminal: https://github.com/opencontainers/runtime-spec/blob/main/config.md#process