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GNOP(8)                 FreeBSD System Manager's Manual                GNOP(8)

     gnop - control utility for NOP GEOM class

     gnop create [-v] [-e error] [-o offset] [-r rfailprob] [-s size]
          [-S secsize] [-w wfailprob] dev ...
     gnop configure [-v] [-e error] [-r rfailprob] [-w wfailprob] prov ...
     gnop destroy [-fv] prov ...
     gnop reset [-v] prov ...
     gnop list
     gnop status
     gnop load
     gnop unload

     The gnop utility is used for setting up transparent providers on existing
     ones.  Its main purpose is testing other GEOM classes, as it allows
     forced provider removal and I/O error simulation with a given
     probability.  It also gathers the following statistics: number of read
     requests, number of write requests, number of bytes read and number of
     bytes written.  In addition, it can be used as a good starting point for
     implementing new GEOM classes.

     The first argument to gnop indicates an action to be performed:

     create         Set up a transparent provider on the given devices.  If
                    the operation succeeds, the new provider should appear
                    with name /dev/<dev>.nop.  The kernel module geom_nop.ko
                    will be loaded if it is not loaded already.

     configure      Configure existing transparent provider.  At the moment it
                    is only used for changing failure probability.

     destroy        Turn off the given transparent providers.

     reset          Reset statistics for the given transparent providers.

     list           See geom(8).

     status         See geom(8).

     load           See geom(8).

     unload         See geom(8).

     Additional options:

     -e error            Specifies the error number to return on failure.

     -f                  Force the removal of the specified provider.

     -o offset           Where to begin on the original provider.

     -r rfailprob        Specifies read failure probability in percent.

     -s size             Size of the transparent provider.

     -S secsize          Sector size of the transparent provider.

     -w wfailprob        Specifies write failure probability in percent.

     -v                  Be more verbose.

     The following sysctl(8) variables can be used to control the behavior of
     the NOP GEOM class.  The default value is shown next to each variable.

     kern.geom.nop.debug: 0
             Debug level of the NOP GEOM class.  This can be set to a number
             between 0 and 2 inclusive.  If set to 0, minimal debug
             information is printed.  If set to 1, basic debug information is
             logged along with the I/O requests that were returned as errors.
             If set to 2, the maximum amount of debug information is printed
             including all I/O requests.

     Exit status is 0 on success, and 1 if the command fails.

     The following example shows how to create a transparent provider for disk
     /dev/da0 with 50% write failure probability, and how to destroy it.

           gnop create -v -w 50 da0
           gnop destroy -v da0.nop

     The traffic statistics for the given transparent providers can be
     obtained with the list command.  The example below shows the number of
     bytes written with newfs(8):

           gnop create da0
           newfs /dev/da0.nop
           gnop list

     geom(4), geom(8)

     The gnop utility appeared in FreeBSD 5.3.

     Pawel Jakub Dawidek <>

FreeBSD 11.0-PRERELEASE         April 14, 2013         FreeBSD 11.0-PRERELEASE


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