The infamous book "Unix Hater's Handbook"xi gives the following example of a simple DoS attack (using recursion): #!/bin/sh $0 & exec $0 The author continues: "once they (these attacks) are launched, the only way to regain control of your Unix system is by pulling the plug beacuse no one can run the ps command to obtain the process numbers of the offending processes... No one can even run the su command to become Superuser!... And best of all, any Unix user can launcg this attack." I thought that this type of problems were fixed in Linux (by limiting child processes etc) and I think that I tested this variant some years ago and the system refused to "go down". I therefore got an unpleasant surprise When one of my students run the following variant while true ; do sleep 5000 & echo "sleep" done and got the system on it's knees. I tested the "Hater" variant and it "worked" too. The error message given from the system when running the sleep variant was: Too many open files in system cannot redirect standard input from /dev/null: Too many open files in system ./testsleep: /bin/sleep: Too many open files in system The "classical" script gives similiar messages. The kernels tested are 2.2.19 and 2.4.10-25 and both give the same result. Something for the kernel people to consider???!!! Best regards Martin F