v0.9.2 signal forwarder doesn't support --pidns

[AkihiroSuda]

#127 doesn't support --pidns.

Without --pidns (works as expected)

$ dockerd-rootless.sh --experimental
...
INFO[2020-03-15T11:02:42.263959577+09:00] API listen on /run/user/1001/docker.sock     
^CINFO[2020-03-15T11:02:43.493624366+09:00] Processing signal 'interrupt'                
INFO[2020-03-15T11:02:43.494655209+09:00] Processing signal 'interrupt'                
INFO[2020-03-15T11:02:43.495386457+09:00] stopping event stream following graceful shutdown  error="<nil>" module=libcontainerd namespace=moby
INFO[2020-03-15T11:02:43.495546067+09:00] Daemon shutdown complete                     
INFO[2020-03-15T11:02:43.495566660+09:00] stopping event stream following graceful shutdown  error="context canceled" module=libcontainerd namespace=plugins.moby
INFO[2020-03-15T11:02:43.495587614+09:00] stopping healthcheck following graceful shutdown  module=libcontainerd
INFO[2020-03-15T11:02:43.495986508+09:00] Processing signal 'interrupt'
$ echo $?
0

With --pidns (unexpected failure)

$ DOCKERD_ROOTLESS_ROOTLESSKIT_FLAGS=--pidns dockerd-rootless.sh --experimental
...
INFO[2020-03-15T13:28:53.859447390+09:00] API listen on /run/user/1001/docker.sock     
^CINFO[2020-03-15T13:28:54.892282069+09:00] Processing signal 'interrupt'                
INFO[2020-03-15T13:28:54.892349636+09:00] Processing signal 'interrupt'                
INFO[2020-03-15T13:28:54.895970152+09:00] stopping event stream following graceful shutdown  error="<nil>" module=libcontainerd namespace=moby
INFO[2020-03-15T13:28:54.898414592+09:00] Daemon shutdown complete                     
INFO[2020-03-15T13:28:54.898938906+09:00] stopping event stream following graceful shutdown  error="context canceled" module=libcontainerd namespace=plugins.moby
INFO[2020-03-15T13:28:54.899736172+09:00] stopping healthcheck following graceful shutdown  module=libcontainerd
[rootlesskit:child ] error: command [/usr/local/bin/dockerd-rootless.sh --experimental] exited: waitid: no child processes
[rootlesskit:parent] error: child exited: exit status 1
$ echo $?
1

[AkihiroSuda]

@ibuildthecloud Any chance to take a look?

[AkihiroSuda]

Also:

$ rootlesskit --pidns /bin/true
[rootlesskit:child ] error: command [/bin/true] exited: waitid: no child processes
[rootlesskit:parent] error: child exited: exit status 1