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Manual Pages  — GNOP


gnop – control utility for NOP GEOM class



gnop create [-v] [-e error] [-o offset] [-p stripesize] [-P stripeoffset] [-r rfailprob] [-s size] [-S secsize] [-w wfailprob] [-z physpath] 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 statistics on the number of read, write, delete, getattr, flush, and other requests, and the number of bytes read and written. gnop can also 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 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.
-p stripesize
  Value of the stripesize property of the transparent provider.
-P stripeoffset
  Value of the stripeoffset property of the transparent 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.
-z physpath
  Physical path of the transparent provider.


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 <Mt pjd@FreeBSD.org>

GNOP (8) January 17, 2018

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