strace reveals this:

2844 open("//.ssh/known_hosts", O_RDONLY) = -1 ENOENT (No such file or directory)

Looking at the environ of a newly-started x2gobroker:

# hexdump -C /proc/20044/environ 00000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| * 00000840 00 00 00 00 00 00 00 |.......| 00000847 #

So the environment was modified inside python and I have no further clue on what its actual state is, whether the environ array just moved in memory (plausible), or destroyed in-place leaving nothing for paramiko.