On 16Oct2008 18:38, Patrick O'Callaghan <pocallaghan@xxxxxxxxx> wrote:
| 2) What does "kill -0" do? "man kill" doesn't mention this possibilty.
It is the standard way of probing for a process given a pid.
It does everything any other signal does except get delivered to the
process (the process never sees it).
There are three outcomes for the caller:
success:
the process exists
failure:
no such process: the process does not exist
permission denied: the process exists, but you don't own it
You're looking at the wrong man page, BTW.
"man 3p kill" says:
The kill() function shall send a signal to a process or a group of
processes specified by pid. The signal to be sent is specified by sig and
is either one from the list given in <signal.h> or 0. If sig is 0 (the null
signal), error checking is performed but no signal is actually sent. The
null signal can be used to check the validity of pid.
"man 2 kill" says:
If sig is 0, then no signal is sent, but error checking is still
performed.
This behaviour dates from at least V7 UNIX (1970s) and probly earlier.
| 3) The script has an obvious race condition, (i.e. if run from several
| places simultaneously, there is a non-zero probability of starting more
| than one process). This is because running the process and creating the
| pidfile are two separate actions.
Absolutely; I may even have mentioned this when I posted the script for
this user some months ago. But for a single person running a single GUI
it may serve. There are better ways, without races, but they are a bit
more cumbersome to script and to understand.
Cheers,
--
Cameron Simpson <cs@xxxxxxxxxx> DoD#743
http://www.cskk.ezoshosting.com/cs/
It's as if all of Scottish cuisine is based on a dare. - Saturday Night Live
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