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.IX Title "nbddiscard 1"
.TH nbddiscard 1 2025-12-16 libnbd-1.24.0 LIBNBD
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.nh
.SH NAME
nbddiscard, nbdzero \- discard or zero all data on a Network Block Device
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 3
\& nbddiscard [\-c|\-\-check] [\-z|\-\-zero] [\-\-fast\-zero]
\&            [\-q|\-\-quiet] [\-v|\-\-verbose] [\-y|\-\-yes]
\&            [\-o|\-\-offset OFFSET] [\-l|\-\-length LENGTH] NBD\-URI
\&
\& nbddiscard \-V|\-\-version
\&
\& nbddiscard \-h|\-\-help
.Ve
.PP
.Vb 3
\& nbdzero [\-c|\-\-check] [\-\-fast\-zero]
\&         [\-q|\-\-quiet] [\-v|\-\-verbose] [\-y|\-\-yes]
\&         [\-o|\-\-offset OFFSET] [\-l|\-\-length LENGTH] NBD\-URI
\&
\& nbdzero \-V|\-\-version
\&
\& nbdzero \-h|\-\-help
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
nbddiscard discards all data on a Network Block Device (NBD) endpoint.
If supported, this frees up the backing storage and makes the device
completely sparse.  For example, if an NBD server is running locally
on port 10809 you could do:
.PP
.Vb 3
\& $ nbddiscard nbd://localhost
\& PERMANENTLY ERASE everything on nbd://localhost bytes 0 \- 1073741823
\& (y/N)? y
.Ve
.PP
nbdzero is the same, but the data is replaced by allocated, zeroed
blocks.
.PP
\&\fBAll data in the discarded or zeroed region is PERMANENTLY ERASED.\fR
.PP
For information about NBD URIs, see \fBnbd_connect_uri\fR\|(3).
.SH OPTIONS
.IX Header "OPTIONS"
.IP \fB\-c\fR 4
.IX Item "-c"
.PD 0
.IP \fB\-\-check\fR 4
.IX Item "--check"
.PD
Rather than modify the disk, merely check whether it is already sparse,
or with \fI\-z\fR that it already reads as zero.
.IP \fB\-\-fast\-zero\fR 4
.IX Item "--fast-zero"
Attempt fast zero (see \fBnbd_can_fast_zero\fR\|(3)), which implies
\&\fI\-\-zero\fR.
.Sp
Not all servers support the fast zero flag, but those that do promise
that an attempted fast zero operation will either complete more
quickly than explicitly writing zeroes to the image, or that it will
immediately fail because the operation is not inherently faster.
.IP \fB\-h\fR 4
.IX Item "-h"
.PD 0
.IP \fB\-\-help\fR 4
.IX Item "--help"
.PD
Display brief command line help and exit.
.IP "\fB\-l\fR LENGTH" 4
.IX Item "-l LENGTH"
.PD 0
.IP "\fB\-\-length\fR LENGTH" 4
.IX Item "--length LENGTH"
.PD
Instead of discarding to the end of the disk, discard only length
bytes.  You can use the normal suffixes like \f(CW\*(C`K\*(C'\fR, \f(CW\*(C`M\*(C'\fR etc.
.IP "\fB\-o\fR OFFSET" 4
.IX Item "-o OFFSET"
.PD 0
.IP "\fB\-\-offset\fR OFFSET" 4
.IX Item "--offset OFFSET"
.PD
Instead of starting from the beginning of the disk, start at the given
offset.  You can use the normal suffixes like \f(CW\*(C`K\*(C'\fR, \f(CW\*(C`M\*(C'\fR etc.
.IP \fB\-q\fR 4
.IX Item "-q"
.PD 0
.IP \fB\-\-quiet\fR 4
.IX Item "--quiet"
.PD
Quiet mode, do not print any warnings.
.IP \fB\-v\fR 4
.IX Item "-v"
.PD 0
.IP \fB\-\-verbose\fR 4
.IX Item "--verbose"
.PD
Enable verbose libnbd messages.  This has the same effect as setting
the environment variable \f(CW\*(C`LIBNBD_DEBUG=1\*(C'\fR
.IP \fB\-V\fR 4
.IX Item "-V"
.PD 0
.IP \fB\-\-version\fR 4
.IX Item "--version"
.PD
Display the package name and version and exit.
.IP \fB\-y\fR 4
.IX Item "-y"
.PD 0
.IP \fB\-\-yes\fR 4
.IX Item "--yes"
.PD
Assume yes to all questions.  This will proceed straight to erasing
your data.  Use this in scripts to avoid interactivity.
.IP \fB\-z\fR 4
.IX Item "-z"
.PD 0
.IP \fB\-\-zero\fR 4
.IX Item "--zero"
.PD
Zero, instead of discarding.  nbdzero is just nbddiscard with \fI\-z\fR.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBlibnbd\fR\|(3),
\&\fBlibnbd\-python\fR\|(3),
\&\fBnbd_connect_uri\fR\|(3),
\&\fBnbdcopy\fR\|(1),
\&\fBnbddump\fR\|(1),
\&\fBnbdfuse\fR\|(1),
\&\fBnbdinfo\fR\|(1),
\&\fBnbdsh\fR\|(1),
\&\fBnbdublk\fR\|(1),
\&\fBblkdiscard\fR\|(8),
\&\fBqemu\-img\fR\|(1).
.SH AUTHORS
.IX Header "AUTHORS"
Richard W.M. Jones
.SH COPYRIGHT
.IX Header "COPYRIGHT"
Copyright Red Hat
.SH LICENSE
.IX Header "LICENSE"
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2 of the License, or (at your option) any later version.
.PP
This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
Lesser General Public License for more details.
.PP
You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110\-1301 USA