     [file version.texi not included]

Stress
******

Overview of stress
******************

stress is not a benchmark, but is rather a tool designed to put given subsytems under a specified load.  Instances in which this is useful include those in which a system administrator wishes to perform tuning activities, a kernel or libc programmer wishes to evaluate denial of service possibilities, etc.

Invoking stress
***************

The format for running the stress program is:

     stress [OPTION [ARGS]] ...

stress supports the following options:

-?
--help
     Show help information.

--version
     Show version information.

-v
--verbose
     Turn up verbosity.

-q
--quiet
     Turn down verbosity.

-n
--dry-run
     Show what would have been done.

-t SECS
--timeout SECS
     Time out after SECS seconds.

--backoff USECS
     Wait for factor of USECS microseconds before starting work.

-c FORKS
--cpu FORKS
     Spawn FORKS processes each spinning on sqrt().

-i FORKS
--io FORKS
     Spawn FORKS processes each spinning on sync().

-m FORKS
--vm FORKS
     Spawn FORKS processes each spinning on malloc().

--vm-bytes BYTES
     Allocate BYTES number of bytes.  The default is 1.

--vm-hang
     Instruct each vm hog process to go to sleep after allocating memory.  This contrasts with their normal behavior, which is to free the memory and reallocate ad infinitum.  This is useful for simulating low memory conditions on a machine.  For example, the following command allocates 256M of RAM and holds it until killed.

          % stress --vm 2 --vm-bytes 128M --vm-hang

-d FORKS
--hdd FORKS
     Spawn FORKS processes each spinning on write().

--hdd-bytes BYTES
     Write BYTES number of bytes.  The default is 1GB.

--hdd-noclean
     Do not unlink file(s) to which random ASCII data is written.

Note: Suffixes may be s,m,h,d,y (time) or k,m,g (size).

Example invocations
*******************

The simple case is that you just want to bring the system load average up to an arbitrary value.  The following forks 13 processes, each of which spins in a tight loop calculating the sqrt() of a random number acquired with rand().

% stress -c 13

Long options are supported, as well as is making the output less verbose. The following forks 1024 processes, and only reports error messages if any.

% stress --quiet --cpu 1k

To see how your system performs when it is I/O bound, use the -i switch. The following forks 4 processes, each of which spins in a tight loop calling sync(), which is a system call that flushes memory buffers to disk.

% stress -i 4

Multiple hogs may be combined on the same command line.  The following does everything the preceding examples did in one command, but also turns up the verbosity level as well as showing how to cause the command to self-terminate after 1 minute.

% stress -c 13 -i 4 --verbose --timeout 1m

You can write a file of arbitrary length to disk.  The file is created with mkstemp() in the current directory, the default is to unlink it, but unlinking can be overridden with the --hdd-noclean flag.

% stress -d 1 --hdd-noclean --hdd-bytes 13

Large file support is enabled.

% stress -d 1 --hdd-noclean --hdd-bytes 3G

Copying This Manual
*******************

You may copy this manual under the terms of the GNU General Public License.