When starting Apache Felix Karaf, you can see this warning message (cfr. FELIX-2360)
bin/karaf: 326: [[: not found
.
A child instance created by admin:create might not be accessible using the admin:connect command, but the instance is fully operational and can be accessed with a normal ssh client (ssh localhost -p <child instance ssh port number> -l karaf) (cfr. FELIX-2361)