commandserver: use selectors2 Previously, commandserver was using select.select. That could have issue if _sock.fileno() >= FD_SETSIZE (usually 1024), which raises: ValueError: filedescriptor out of range in select() We got that in production today, although it's the code opening that many files to blame, it seems better for commandserver to work in this case. There are multiple way to "solve" it, like preserving a fd with a small number and swap it with sock using dup2(). But upgrading to a modern selector supported by the system seems to be the most correct way.