Any task using a network or distributed filesystem will cause sys_checkpoint() to return failure because the file its fd refers to lacks the .checkpoint file operation. See UncheckpointableFilesystems.
Issues, Solutions, Impacts
|Issue||Solution(s)||Current Impact||Solution Impact|
A userspace NFS server is probably checkpointable so long as it relies on other checkpointable primitives like inet sockets and a checkpointable local filesystem. NFS clients are more problematic since they require special kernel support.