-echo=string, and sleep=value. Any number of `--checkpoint-action'
-options can be specified, the actions will be executed in order of
-their appearance in the command line.
+echo=string, ttyout=string, exec=cmdline, and sleep=value. Any number
+of `--checkpoint-action' options can be specified, the actions will be
+executed in order of their appearance in the command line. See
+chapter 3.8 "Checkpoints" for a complete description.