I'm trying to use py-spy on a python process already running py-spy dump -p 219292.

That process make use of user name space. That probably explain why py-spy is failing.

1. I'm question if it's possible to use py-spy cross namespace ?
2. Would it be possible to handle the exception and continue the "spying" event if some file are not found ?

Running with strace:

# strace -e trace=open py-spy dump -p 219292
open("/proc/219292/maps", O_RDONLY|O_CLOEXEC) = 3
open("/proc/219292/exe", O_RDONLY|O_CLOEXEC) = 3
open("/proc/219292/root/tmp/minarca-jail-ku6ln2cg/opt/rdiff-backup-2.0/libpython3.7m.so.1.0", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
Error: No such file or directory (os error 2)
+++ exited with 1 +++

/tmp/minarca-jail-ku6ln2cg/opt/rdiff-backup-2.0/libpython3.7m.so.1.0 doesn't exists. It's probably only mounted in the namespace