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.\"
.IX Title "nbdkit-readonly-filter 1"
.TH nbdkit-readonly-filter 1 2024-05-10 nbdkit-1.38.2 NBDKIT
.\" 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
nbdkit\-readonly\-filter \- switch a plugin between read\-only and writable
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 1
\& nbdkit \-\-filter=readonly PLUGIN
\&
\& nbdkit \-\-filter=readonly PLUGIN readonly\-file=/tmp/ro
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
\&\f(CW\*(C`nbdkit\-readonly\-filter\*(C'\fR is an nbdkit filter that has two modes:
.IP \(bu 4
When the \f(CW\*(C`readonly\-file\*(C'\fR parameter is \fBnot\fR used, make the
underlying plugin completely read-only.  This is similar to using the
nbdkit \fI\-r\fR option on the command line.
.IP \(bu 4
When the \f(CW\*(C`readonly\-file\*(C'\fR parameter is used, make the underlying
plugin read-only when that file is present on disk, but leave it
writable when the file is not present (or if the file is deleted).
This way you can switch a plugin between being writable and
write-protected at run time.
.PP
Trying to write to the filter when the filter is enforcing read-only
mode will cause \f(CW\*(C`EPERM\*(C'\fR ("Operation not permitted") to be returned to
the client.
.PP
\&\fBnbdkit\-protect\-filter\fR\|(1) is a related filter which can
write-protect parts of a plugin (eg only the boot sector).
\&\fBnbdkit\-error\-filter\fR\|(1) is another filter which can be used for the
same purpose as this filter but is more complicated to use.  See also
the \fI\-r\fR option described in the \fBnbdkit\fR\|(1) manual.
.SH EXAMPLE
.IX Header "EXAMPLE"
Make a disk read-only 60 seconds after nbdkit is started:
.PP
.Vb 3
\& rm \-f /tmp/ro
\& nbdkit \-\-filter=readonly file disk.img readonly\-file=/tmp/ro
\& sleep 60; touch /tmp/ro
.Ve
.SH PARAMETERS
.IX Header "PARAMETERS"
.IP \fBreadonly\-file=\fRPATHNAME 4
.IX Item "readonly-file=PATHNAME"
If this parameter is used, the filter makes the underlying plugin
read-only when \fIPATHNAME\fR exists, otherwise the plugin is writable as
usual.
.Sp
If this parameter is not used, the filter always makes the underlying
plugin read-only.
.SH FILES
.IX Header "FILES"
.ie n .IP \fR\fI$filterdir\fR\fI/nbdkit\-readonly\-filter.so\fR 4
.el .IP \fR\f(CI$filterdir\fR\fI/nbdkit\-readonly\-filter.so\fR 4
.IX Item "$filterdir/nbdkit-readonly-filter.so"
The filter.
.Sp
Use \f(CW\*(C`nbdkit \-\-dump\-config\*(C'\fR to find the location of \f(CW$filterdir\fR.
.SH VERSION
.IX Header "VERSION"
\&\f(CW\*(C`nbdkit\-readonly\-filter\*(C'\fR first appeared in nbdkit 1.38.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBnbdkit\fR\|(1),
\&\fBnbdkit\-error\-filter\fR\|(1),
\&\fBnbdkit\-file\-plugin\fR\|(1),
\&\fBnbdkit\-full\-plugin\fR\|(1),
\&\fBnbdkit\-protect\-filter\fR\|(1),
\&\fBnbdkit\-filter\fR\|(3).
.SH AUTHORS
.IX Header "AUTHORS"
Richard W.M. Jones
.SH COPYRIGHT
.IX Header "COPYRIGHT"
Copyright Red Hat
.SH LICENSE
.IX Header "LICENSE"
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
met:
.IP \(bu 4
Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
.IP \(bu 4
Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
.IP \(bu 4
Neither the name of Red Hat nor the names of its contributors may be
used to endorse or promote products derived from this software without
specific prior written permission.
.PP
THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR
CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
SUCH DAMAGE.