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FUZZ(1) FreeBSD General Commands Manual FUZZ(1)

fuzz - stress test programs

fuzz [-t|--timeout timeinsecs] [-p|--printable] [-n|--newlines] [-l|--length totlen] [-m|--maxline maxlinelen] [-r|--runcount numruns] [-b|--bytes] [-c|--chroot] [-u|--user username] [-a|--args] [-o|--omitdata] [-e|--execute filename] [-x|--maxargs numargs] [-d|--dontask] [-y|--mararglen arglen] [-V|--version] [-i|--priority] target targetarg...

fuzz is a program designed to find bugs in other programs. It does this by doing a form of black box testing. It does this by running the target program multiple times and passing it random input. Right now this can come from one of two places, stdin and the command line arguments. Testing completes whenever the program either the requested number of runs finishes successufully or the program crashes.

Any arguments following the target program are passed directly to the target program.

-t, --timeout TIME
This sets the number of seconds that the fuzz will wait for the other program before it assumes that the program is hung. The default value is 120 seconds. This is sensing of when a program is hung is not entirely reliable. See the BUGS section.
-p, --printable
This limits both the stdin and the command line arguments to only printable characters. By default fuzz passes fully random bytes into the target program.
-n, --newlines
Include random newlines in the input stream.
-l, --length LENGTH
The length in bytes of the data stream to pass through stdin into the target program. The default length is 100K.
-m, --maxline MAXLINELEN
Specify the maximum line length within the random data stream passed into stdin.
-r, --runcount RUNCOUNT
The number of times to run the target program. The default is 10,000.
-b, --bytes
In addition to counting through the number of runs. Count through the bytes being sent through stdin to the program. This option really serves no purpose other than making something interesting to watch.
-c, --chroot
Since there is no telling what a program will do when given random input. this allows a program to be sort of caged while it is run so that the damage that it may be able to do is minimized. This requires that the fuzz be run as root. It will drop privlages before it runs the test program. This option is best used in conjunction with the --user option. This often times requires that a program is statically linked.
-u, --user USERNAME
Since there is no telling what a program will do when given random input, this specifies what user the target program will be run as so that it is easy to find and repair anything that may have been scribbled across your file system. This option was designed to be used in conjuntion with the --chroot option and will only work if fuzz is run as root.
-a, --args
In addition to passing random data via stdin, pass random command line arguments. This simply sets the number or random arguments to be passed to 256. See the BUGS section.
-o, --omitdata
Some programs don't take input from stdin. They only take input from the command line arguments. If this is the case simply use the --omitdata option.
-x. --maxargs NUMARGS
This is to set the maximum number of arguments that are passed to each invocation of the target program.
-y, --maxarglen ARGLEN
Sets the maximum length of an arguments passed to the target program.
-V, --version
Print the version of fuzz and exit.
-i, --priority
Run at a specified priority.
-d, --dontask
In the cases where the target program is for sure part of a package and the packaging information will provide the needed version information then you can use this option to avoid being asked what the version is.

fuzz grep foo
fuzz -c -u nobody cpio -i

The random arg functions doesn't work very well right now. The arguments passed are so random that the program usually just prints out the usage message and then terminates. This will become much more useful later when we are mating data sets with the intention of maximizing code coverage.

Ben Woodard <>

November 3, 1999 3rd Berkeley Distribution

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