kyle-qmail at memoryhole
Nov 17, 2009, 11:32 AM
Post #2 of 2
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On Wednesday, November 18 at 04:48 AM, quoth Philip Rhoades:
>exec /usr/local/bin/softlimit -m 32000000 \
> /usr/local/bin/tcpserver -v -R -H -l "$LOCAL" \
> -x /etc/tcp.smtp.cdb -c "$MAXSMTPD" \
> -u "$QMAILDUID" -g "$NOFILESGID" 0 smtp \
> /usr/local/bin/greylite \
> /var/qmail/bin/qmail-smtpd 2> /var/log/greylite.log
>
>- when tcpserver processes the prog arguments - in this case the
>greylite prog - does how greylite exits determine if the next program,
>in this case qmail-smtpd, is run?
The way this works is a process often referred to as "exec chaining".
In essence, tcpserver looks at all its arguments, and runs the
following command:
/usr/local/bin/greylite /var/qmail/bin/qmail-smtpd
In other words, it runs one program with one argument. That's all it
ever does (well, okay, some people make it pass more arguments). Thus,
tcpserver does nothing complex, and makes no decisions at all.
Then greylite runs, makes its decision, and then (based on that
decision) executes the program listed in ITS arguments (or not,
depending on what greylite decided to do).
This works very similar to the way sudo works. For example, consider
the following command:
sudo bash -c "echo foo"
Your question is akin to asking "how does sudo know when to run
echo?". The answer, of course, is that it doesn't, because it doesn't
need to.
Does that make sense?
~Kyle
- --
The sacred rights of mankind are not to be rummaged for, among old
parchments, or musty records. They are written, as with a sun beam in
the whole volume of human nature, by the hand of the divinity itself;
and can never be erased or obscured by mortal power.
-- Alexander Hamilton, 1775
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