nbdkit-readonly-filter(1)

📦
version 1.48.1 · 11 versions
, in fedora 44

💖 nbdkit-readonly-filter 💖

okay so bestie, we're in the NBDKIT manual and today's main character is nbdkit-readonly-filter — a whole filter whose entire personality is flipping a plugin between writable and read-only. iconic behaviour honestly ✨

🌸 NAME 🌸

nbdkit-readonly-filter — switch a plugin between read-only and writable

🎀 SYNOPSIS 🎀

nbdkit --filter=readonly PLUGIN

nbdkit --filter=readonly PLUGIN readonly-file=/tmp/ro

💅 DESCRIPTION 💅

nbdkit-readonly-filter is an nbdkit filter, and it has two modes, like two moods, and honestly both of them eat:

  • When the readonly-file parameter is not used, it makes the underlying plugin completely read-only. this is giving the same energy as using the nbdkit -r option on the command line 🫶
  • When the readonly-file parameter is used, the underlying plugin goes read-only whenever that file is present on disk, and stays writable when the file isn't there (or when the file gets deleted). so you can switch a plugin between writable and write-protected at run time, no restart, no drama. 💅

Trying to write to the filter while it's enforcing read-only mode will cause EPERM (Operation not permitted) to be returned to the client. so like, rude of you to try, and the filter WILL tell on you. 😭

ngl there's a whole friend group of related filters. nbdkit-protect-filter(1) is the related one that can write-protect parts of a plugin (eg only the boot sector). nbdkit-error-filter(1) is another filter you could use for the same purpose as this one, but it's lowkey more complicated to use. also go read the -r option described in the nbdkit(1) manual. iykyk 🦋

✨ EXAMPLE ✨

Make a disk read-only 60 seconds after nbdkit is started:

rm -f /tmp/ro
nbdkit --filter=readonly file disk.img readonly-file=/tmp/ro
sleep 60; touch /tmp/ro

see that? touch and boom, she's read-only. the way that works is genuinely so satisfying 🍓

🧚 PARAMETERS 🧚

  • readonly-file=PATHNAME — If this parameter is used, the filter makes the underlying plugin read-only when PATHNAME exists, otherwise the plugin is writable as usual. If this parameter is not used, the filter always makes the underlying plugin read-only. (PATHNAME is the file the filter keeps an eye on — present = locked down, absent = business as usual.) 👑

🌈 FILES 🌈

  • $filterdir/nbdkit-readonly-filter.so — The filter.

Use nbdkit --dump-config to find the location of $filterdir. 🎀

⭐ VERSION ⭐

nbdkit-readonly-filter first appeared in nbdkit 1.38.

💜 SEE ALSO 💜

nbdkit(1), nbdkit-error-filter(1), nbdkit-file-plugin(1), nbdkit-full-plugin(1), nbdkit-protect-filter(1), nbdkit-filter(3).

👑 AUTHORS 👑

Richard W.M. Jones

Copyright Red Hat

📜 LICENSE 📜

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

  • Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
  • 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.
  • 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.
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.

okay that's the whole page bestie, we ate and left no crumbs 💖 this was nbdkit-readonly-filter(1) from nbdkit 1.48.1, dated 2026-08-29 — go forth and write-protect responsibly, mwah 🌸💅✨

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