just wondering this while driving my car today ...

purpleburple · 07-31-2002, 12:21 AM

Hi. Im new (sorta) 5months or so ) to linux and begining C programming (8 months on/off) and wanna learn bash and python and eventually assembly.
Anyways I was driving today listening to the Deftones (which I burned on linux using mkisofs and cdrecord ) (no front-ends for me) ( <--- none of this has anything to do with my question by the way) and a question came to my mind about programming. > Is it possible to have a program sit on a HDD and
auto-execute after a certain amount of time (say a month or so) or would it have to be running for the clock to do the counting (for the month or whatever) ? I mean without the help of any other programs. I think the answer would be NO. Just wanted to know what any experienced programmers new.

thanks

lackluster · 07-31-2002, 12:24 AM

from what I've read of the man pages, you mean a "cron job".

$man cron

purpleburple · 07-31-2002, 12:30 AM

thanks

Mik · 07-31-2002, 04:21 AM

Well cron is an application. It just checks if it has any scheduled events and executes them at the appropriate time. So making it a cron job will be running it with the help of another application.

There has to be something that triggers the execution of an application. Since the kernel doesn't do this it's up to other applications to do this. Most people use cron (or a cron like program) to execute applications at a scheduled time.

llama_meme · 07-31-2002, 07:38 AM

You could write a kernel module which executed the application periodically, but there'd be no point, obviously...

lackluster · 07-31-2002, 10:09 AM

Speaking of modules, how could I compile one? THere is an example in this book I have but I fear the 2.4.18 kernel has it's diffrences. I tried

Code:

gcc -o first.o first.c -D__KERNEL__ -I/usr/src/linux/include -DMODULE -Wall -O2

but no luck .... just alot of link errors

Mara · 07-31-2002, 02:35 PM

It's a problem with PATH. What directory was the module in? How is your library path set (in ld.so.conf)?

lackluster · 07-31-2002, 11:58 PM

the module source is in [way] under my home directory :
/home/lackluster/cstuff/modules/first.c

I don't get your second question. This is the contents of it :

Code:

/usr/local/lib
/usr/X11R6/lib
/usr/i386-slackware-linux/lib
/opt/gnome/lib
/usr/openwin/lib
/usr/lib/qt/lib
/opt/kde/lib

Mara · 08-01-2002, 04:57 AM

ld.conf.so looks good.
Are you sure that /usr/src/linux is the directory with the right version of kernel? The one your module is for?
Module for 2.2.x kernel won't work with 2.4.x kernel....

kgwagner · 08-01-2002, 07:06 AM

You're right - the answer is no. Something has to be running, keeping track of time - either the app your want to start percolating, or cron (or something like it). Cron already works, so...

You could have your app run, keeping track of time until some fateful moment, but it's likely it would consume considerably more resources than cron would to do the same thing.

Incidentally, there are a number of calendar programs you can have start at boot that will pop reminders for you, if that's where you're going with this.

lackluster · 08-01-2002, 10:27 AM

Quote:

Originally posted by Mara
ld.conf.so looks good.
Are you sure that /usr/src/linux is the directory with the right version of kernel? The one your module is for?
Module for 2.2.x kernel won't work with 2.4.x kernel....

yeah /usr/src/linux is 2.4.18 (I should know I've built it enough

). The module isn't for any specific kernel. This is what I found in this book thus this is what I've tried :

{ first.c }

Code:

#include <linux/module.h>

#if defined(CONFIG_SMP)
#define __SMP__
#endif

#if defined(CONFIG_MODVERSIONS)
#define MODVERSIONS
#include <linux/modversions.h>
#endif

#include <linux/kernel.h>

int init_module(void) {
	printk(KERN_DEBUG "Hello, Kernel!\n");
	return 0;
}

void cleanup_module(void) {
	printk(KERN_DEBUG "Later, Kernel!\n");
}

Mara · 08-01-2002, 01:25 PM

The code looks good (for an 2.2.x module, but should be also good for 2.4.x). Could you paste your error messages? It seems it's all about pathes.

lackluster · 08-01-2002, 01:28 PM

sh-2.05a$ make
gcc -o first.o first.c -D__KERNEL__ -I/usr/src/linux/include \
-DMODULE -Wall -O2
/usr/lib/crt1.o: In function `_start':
/usr/lib/crt1.o(.text+0x18): undefined reference to `main'
/tmp/cca6ySeP.o: In function `init_module':
/tmp/cca6ySeP.o(.text+0xf): undefined reference to `printk_R1b7d4074'
/tmp/cca6ySeP.o: In function `cleanup_module':
/tmp/cca6ySeP.o(.text+0x27): undefined reference to `printk_R1b7d4074'
collect2: ld returned 1 exit status
make: *** [first.o] Error 1

Mara · 08-01-2002, 02:28 PM

Try this:
gcc -Wall -DMODULE -D__KERNEL__ -DLINUX -O2 -I/usr/src/linux/include -c first.c
I compiled it on my machine this way (kernel 2.2.20), but should work also for you.

lackluster · 08-01-2002, 05:33 PM

Ah so! Your patience and help is much appreciated, Mara. It worked. The only difference I see here is that you defined LINUX (-DLINUX). What's that about? Anyways, thanks greatly for your help - hopefully someday I'll make a driver you'll want/need and then you'll be glad you helped me so long back

. You rock.