[SOLVED] Too many forks, pid got used, we're confused

Aquarius_Girl · 09-01-2010, 06:29 AM

Quote:

Originally Posted by druuna

Hi,

This tool (ulimit) will not necessarily stop the initial process, it will limit the use of resource for a user or a specific terminal.

The message you get (also mentioned in the link I gave) tells you that a limit is reached. And even though that specific terminal might become unresponsive, other terminals and the machine itself are not compromised by, in this example, a bash fork bomb.

You could compare it with making a building fire proof: You can have a blazing fire in one room (which is destroyed, most of the time) but the adjacent rooms and building itself survive.

Thanks for the effort !

This time I ran :

Code:

anisha@linux-uitj:~> su
Password:
linux-uitj:/home/anisha # ulimit -u 15
linux-uitj:/home/anisha #

I again compiled the project without modifying "Libtool".
Then I did ps -el which showed the same *very lenghty* output !!

Why ??

When I set ulimit to 15 then does it not mean that hanging libtool can create only 15 processes ?

Not only that terminal but whole system started getting very slow !!

druuna · 09-01-2010, 06:44 AM

Hi,

Count yourself lucky that you can still do something!

Although I had a feeling this would happen, I did become root (full login: su -), executed ulimit -u 30 and executed the fork bomb. Result: End of story within a second. I needed a hard reset to reboot my machine (don't you just love ext3 and the journal recovery

it would have taken a while with ext2 and fsck on 12 partitions..... )

Root, as you should know, is a special user and should not be used for day to day tasks. Maybe ulimit can be set up for root, but restricting a user that is unrestricted doesn't sound/feel good.

Hope this helps.

Aquarius_Girl · 09-01-2010, 07:16 AM

I am not still understanding the purpose of "ulimit" !

I ran it without root too but still the system was getting *slow* though *slowly* !

1. When it can't prevent other processes from "hanging/getting slow" then what's the use ?
2. Should the KDevelop be also launched from the same shell to see some effects of ulimit ?
3. Does "ulimit" has to started every time we restart computer ? Can't we set and fix the value somewhere ?

druuna · 09-01-2010, 07:46 AM

Hi,

Quote:

I am not still understanding the purpose of "ulimit" !

It is there to protect other users and the machine itself, it is _not_ necessarily meant to stop processes. Also see my previous reply:

- This tool (ulimit) will not necessarily stop the initial process, it will limit the use of resource for a user or a specific terminal.
And:
- I'm not sure, but I would understand if the following scenario where true: Process A forks a sub-process B. Process B starts forking multiple processes (loop, intentional or not). Ulimit kills Process B and its children when reaching the limit, but process A remains.

Quote:

3. Does "ulimit" has to started every time we restart computer ? Can't we set and fix the value somewhere ?

Yes, but you do not have to do this yourself.

I haven't used suse in a long time, but I do believe this is the place to check: /var/adm/fillup-templates/sysconfig.ulimit also have a look here: ulimit - Set per-process limits (ulimits) [openSuse].

Hope this helps.