some strange reason.
solves the problem. Otherwise the following error message is reported:
sh: vmstat: command not found
Use of uninitialized value $swap_out in pattern match (m//) at /usr/local/bin/parallel line 2164.
Use of uninitialized value $swap_out in pattern match (m//) at /usr/local/bin/parallel line 2164.
[and several more of those]