A more general question

i don’t really know where to ask this question and i don’t see any answer in documentation i have read so far. i am assuming a root process can become a member of a container after the container exists. if a process creates an unnamed pipe (2 fds) and then forks a child process, with each process then closing one of the pipe fds to have a pipe going between them … maybe 2 such pipes (1 in each direction) … can one of these processes join the existing contain resulting communication between (a process in) the container and (a process in) the host (a maybe another container) without having networking set up (such as no bridge and/or no interfaces in the container)?

Yes, you can absolutely spawn a process outside a container, setup a PIPE or any other fd, then fork() and attach the child to the container, keeping the fd open to the host.

thanks. that seems like a choice in setting up an image in a container in certain cases when a bind mounted tree is awkward, such as LFS.

Useful post. Thanks for the Information.