Placeholder for OCI changes
The create command is documented in the
spec
as requiring two positional arguments: <container-id> <path-to-bundle>.
However, runc (the reference implementation of the spec) accepts only a single
positional argument (<container-id>) and instead uses either the current
working directory as the bundle or accepts it through the -b/bundle flag.
See here.
The spec does not describe how container STDIO should be handled. runc passes
the STDIO file descriptors for the runc create invocation to the container
process. Programs that invoke runc (like containerd) configure STDIO for runc create and provide input/collect output for the container through those
descriptors.
The spec includes a terminal field, but does not describe how a runtime should
expose the terminal. runc expects an AF_UNIX socket to be provided as a
command-line argument in the --console-socket field; runc's init process is
responsible for allocating a pty and sending the control device's file
descriptor over the provided socket.
runc opens the socket file as part of runc create, then passes that socket
file as an extra file descriptor when starting the init process, indicating the
fd number with the _LIBCONTAINER_CONSOLE environment variable. The init
process creates the pty (console.NewPty), sends the control fd number to the
socket (utils.SendFd), and uses dup3(2) to override the standard I/O file
descriptors (0, 1, and 2) for the container process.
A runc client like containerd-shim-runc-v2 is responsible for creating the
socket passed as --console-socket (with pkg/process/init.go:Create),
receiving the control device (with socket.ReceiveMaster), then copying bytes
to and from the device.
runc's implementation of the start command exits immediately after starting the container's process. This does not appear to be specified in the spec.