Autzoo.1581 net.bugs.v7 utzoo!henry Mon Apr 19 18:58:48 1982 kill -1 -1 The V7 kill program will not take -1 as a processid. The kill system call likes it just fine (it sends the signal to all processes except 0 and 1) but kill(1) thinks it is syntactically invalid. The fix for this is to change the line: if (**argv<'0' || **argv>'9') to something like: if (!isdigit(**argv) && **argv != '-') (NB if you use isdigit rather than the explicit 0 and 9, you'll need to #include .)