[lug] dumb q....echo 1?

[j davis]

thankk you i think i got a better idea of whats happening now.
jd


>From: rm at fabula.de
>Reply-To: lug at lug.boulder.co.us
>To: lug at lug.boulder.co.us
>Subject: Re: [lug] dumb q....echo 1?
>Date: Thu, 4 Apr 2002 13:26:43 +0200
>
>On Thu, Apr 04, 2002 at 07:36:01AM +0000, j davis wrote:
> >
> > hi,
> >
> > so im rebulding my firwall with the help of the best iptables how
> > to i have ever read
> > http://www.boingworld.com/workshops/linux/iptables-tutorial (thats quite 
>a
> > few now). Anyway in a example script
> > this is used
> >
> > echo "1" > /proc/sys/net/ipv4/ip_forward
> >
> > so i think the text "ip_forward" is being written to 
>/proc/sys/net/ipv4..
> > what is the "1" for? Also proc is the ram right? could some one explain
> > why i have to do this and what is really happening when i do this...not
> > just "uh,
> > thats how you start iptables"...like could some one tell me if im 
>loading a
> > module
> > into ram...and why i need the "1" after echo.
> >
> > thanks for the help and yalls patients,
> > jd
>
>Since nobody answered this yet, let me try to:
>
>  /proc isn't really the RAM, under Linux (and Unix) no program has direct
>access to the systems RAM, only the kernel (the operating system) has. 
>When-
>ever a program (process) needs to access the RAM (or any other system 
>resource,
>like the keyboard, mouse, network or soundcard erc.) it needs to ask the 
>kernel
>to do so. So it's up to the kernel to provide an interface to programs 
>(often
>called 'userspace') that enables them to get their job done. The 'classic' 
>way of
>doing this is by means of so-called system calls -- a set of programming
>routines that let a program comunicate with the kernel (as an example have 
>a look
>at 'man 2 open', a system call (or better, a wrapper arround a system call) 
>to
>open a specific file). Now, for some tasks the single function aproach to 
>comuincation
>with the kernel would be rather clumsy (esp. when the kernel needs to 
>provide rather
>complex and highly strucutred information). For these cases the Linux 
>kernel has the
>proc interface which to the user looks like a (pseudo)-filesystem. As a 
>kernel(module)
>programmer you can create a set of functions and install a pseudo-file in 
>the proc
>system to comunicate with userspace programs. Now, whenever someone reads 
>or writes
>to the proc file your created one of your functions get called and you can 
>handle the
>request.
>
>/proc/sys/net/ipv4 :
>  Type 'cat /proc/sys/net/ipv4/ip_masq_debug' you'll probably se a '0'. 
>This is a
>  logical flag, indicating that this feature is currently switched off. 
>Once you
>  'echo "1" > /proc/sys/net/ipv4/ip_masq_debug' ip masquerading debugging 
>is switched
>  on. This is a much easier interface than having to write a special 
>program that emits
>  system calls to change this value.
>  So, to answer your question: "1" is just an indication that you want 
>something switched
>  on (an old C programming habit: everything that's not '0' is true/on).
>
>
>Hope this is of any help
>
>    Ralf Mattes
>
> >
> >
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