Cron jobs too heavy for ordinary systems (system completely unusable for a while)

[Vincenzo Ciancia]

Hi all,

I am running jaunty. Sometimes, randomly, the disk starts spinning (I
hear the noise and see the light) and the system becomes unusable.
Often, to gain control of a shell (even in console) is a matter of
waiting minutes and eventually, when I finally can do some "top" "iotop"
or "ps" to understand what's happening, the storms is already calmed and
I can't see anything. I am not running trackerd on this machine (and
with last year of development, it's rarely the culprit).

This time I did that in time, while thinking "be it the kernel itself, I
apt-get remove it". I found that cron jobs where running. I am seriously
tempted to apt-get remove anacron :) But it seems to me that the apt
automatic update is the problem. I will try disabling it. 

At the end of the storm, I can see this:

vincenzo at frattaglia:~$ free
             total       used       free     shared    buffers
cached
Mem:       1017884     987568      30316          0      16544
651836
-/+ buffers/cache:     319188     698696
Swap:      1887596    1884040       3556


So yes, an hurricane has passed in my poor 1gb of memory, leaving almost
2gb of trash in my swap partition.

This problem makes ubuntu reach the bottom of its user experience. From
an end-user point of view, you are working, and your system trashes. It
takes several seconds to even get the focus to an existing terminal if
any. There's nothing else to say, this must not happen. Cron jobs should
not be able to take over a system. 

How could this be solved? Would a smart use of the "nice" command be
enough? 

Vincenzo