Adeodato Simó wrote: > * Bob Proulx [Thu, 07 Jul 2005 21:24:07 -0600]: > > > * why the different implementations? > > > It is there for BSD job control functionality. That way you can say > > 'kill %1' and kill the background jobs by job control number. The > > standalone version does not know about the shell's list of jobs. > > I also have heard (but I'm not sure how often does this happen, if at > all) that it is usefult to have it as a built-in when your system is > in a state when it can't create more processes.
The v7 shell did not have a built-in kill. But having it built-in as with later shells is certainly useful at times for the purpose you state. But the problem is finding the number of the process to kill. With /proc available to get process id numbers with 'echo /proc/*' which does not spawn a new process this is easier than in the old days from pstat*(2) and a standalone 'ps' process. Because without /proc and needing to run 'ps' to get a listing of processes if you had a full process table you could not run ps and could not find the process id to kill easily. Too many times I have seen "cannot fork" messages from the shell. But if you knew a process id that you could kill to gain a few more process slots then even in the v7 shell you had a way to kill it. The technique showed to me from an experienced unix hacker when I was learning this was 'exec kill -9 ##'. By using the running shell for the process you get one attempt for the command so better make it effective. :-) Bob
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