The "sync" support should be done asynchronously, not with waitpid.

introduce a new exec command to tell minit to execve() a new version of
  it without reboot

if hwclock is used to adjust the system clock by a few hours, the minit
  times will be completely off.  Maybe we should use the poll timeout to
  keep track of what we think how long we are running and use that as a
  basis to find out and correct this?
