Changing limits with ulimit (Lab 3.1)

gacanepa

Hi everyone,

I am a bit unclear as to why exercise #4 in lab 3.1 results in an operation not permitted error. The solution states, "Note that if we had chosen a different limit, such as stack size (-s) we could raise back up again as the hard limit is unlimited.". What exactly does stack size refer to and how does it make a difference?

Thanks in advance.

luisviveropena

Hi,

From the documentation:

 ulimit [-HSTabcdefilmnpqrstuvx [limit]]

              Provides control over the resources  available  to  the  shell  and  to  processes

              started  by it, on systems that allow such control.  The -H and -S options specify

              that the hard or soft limit is set for the given resource.  A hard limit cannot be

              increased  by  a non-root user once it is set; a soft limit may be increased up to

              the value of the hard limit.

==> a soft limit may be increased up to the value of the hard limit.

If you want to take a look, check the man or info page for ulimit.

Regards,

Luis.

gacanepa

Luis,

Please note that my question refers to the meaning of the words stack size, and how that would have made a difference in the proposed lab exercise.

PS: Since ulimit is a shell builtin, it does not have a standalone man page. And as far as I can see, neither the shell builtins' man page nor the info page on ulimit explain the concept of stack size.

coop

you can get info on "ulimit" by typing "help ulimit" as it is a built in bash command.  You can't expect that to exlain what all the possibility parameters do.

 

Stack is the amount of memory avaialble to a process for static variables, such as arrays and other storage.  Every process created is allotted such memory when it starts; by default on Linux 8MB is granted usually -- that is not so much unless you start creating thousands of processes, such as a server might, in which case you might want to limit it.  

The stack is an important *programming* concept in any computing language, but a normal user would not be terribly aware of it.  I'm sure a little bit of googing or look at the wikipedia would give you a deeper undrerstanding of its role in any operating system, nut just Linux.