DragonFly On-Line Manual Pages

FORKBOMB(8)            DragonFly System Manager's Manual           FORKBOMB(8)

NAME
       forkbomb - eat system resources

SYNOPSIS
       forkbomb [options]

AUTHOR
       This program and manual page was written by Radim Kolar hsn@netmag.cz,
       for fun (but may be used for serious tasks).

DESCRIPTION
       forkbomb is a simple resource hog program.

OPTIONS
       The programs follow the usual GNU command line syntax, with long
       options starting with two dashes (`-').  A summary of options are
       included below.

       -?, -h, --help
              Show summary of options.

       -v, --version
              Show version of program.

       --runasroot
              Allows running with euid==0.

       --nosafetyalarm, --infinite
              Run for infinite time.

       -c, --cpuhang
              Eat CPU time. If -M is also used, write to allocated memory
              instead of running infinite loop.

       -f, --forkbomb
              Fork infinite number of self copies.

       -z. --zombie
              Lets go to House of Dead. You can not bring bombs there.

       -m, --allocmemory
              Allocate all available memory.

       -M, --touchmemory
              Write to every page in allocated memory. Implies -m.

       -t, --maxtime <sec>
              Set maximum execution time.

       -l, --memorylimit <MB>
              Set memory allocation limit per process.

       -i, --incpages <num>
              Allocate memory in groups of num pages.

       --quit Don't wait for safety alarm expiration (useful only with -m/-M
              option for realloc() benchmarking)

EXIT STATUS
       0 - your system has survived.

       1 - Insufficient RTFM detected.

CLASSICS FORKBOMB
       forkbomb -f

       Linux 2.4
              crash. Can not switch virtual console, can not ping, death.

       Linux 2.6
              do not crash but runs very slowly.

       FreeBSD 5.2
              Excellent result, runs with only small slowdown.

       FreeBSD 5.4
              allocates too much wired memory and that hangs the system. Hang
              is not that good as in Linux 2.4, because you can switch virtual
              consoles.

PLAIN REALLOC RESULTS
       forkbomb -m -l 32 -i 256 --quit

       Linux 2.4, 2.6
              I have tested then only with glibc 2.3.2 and results are
              excellent. Both finished test with instantly with 0.00 CPU time.

       FreeBSD 5.2
              The realloc() has several serious problems. First problem is
              that realloc is really slow, It needs 12 seconds to run this
              test. It looks like it unnecessary copies data on reallocation.
              Second problem is if you allocate more than -l 18 MB of memory,
              malloc eats about 3 times more memory from system than needed.
              Maybe this have something to do with size of malloc cache size
              (default 16 pages). FreeBSD people should really look at their
              libc/stdlib/malloc.c

REALLOC WITH TOUCH
       forkbomb -l 32 -i 256 -M --quit

       Linux 2.4, 2.6
              Linux is also super fast there, test run is 0.3 sec. Linux
              allocates bigger memory blocks directly from mmap and uses
              mremap for resizing. There is no need for copying data around.

       FreeBSD 5.2
              FreeBSD runs for 9.9 seconds which is FASTER that without
              touching memory at all.

HUNGRY FORKBOMBS
       forkbomb -f -c

       Linux 2.4
              dead.

       Linux 2.6
              ls command takes between 100 to 200 seconds. System load was
              840.

       FreeBSD 5.2
              ls command takes 70 seconds to execute. System load was 800.

TODO
       Incorporate user feedback.

COPYING
       Forkbomb program and this manual page are both public domain.

                                  13 May 2005                      FORKBOMB(8)