About me: My name is Solène Rapenne, pronouns she/her. I like learning and sharing knowledge. Hobbies: '(BSD OpenBSD Qubes OS Lisp cmdline gaming security QubesOS internet-stuff). I love percent and lambda characters. OpenBSD developer solene@. No AI is involved in this blog.

Contact me: solene at dataswamp dot org or @solene@bsd.network (mastodon).

I'm a freelance OpenBSD, FreeBSD, Linux and Qubes OS consultant, this includes DevOps, DevSecOps, technical writing or documentation work.

If you enjoy this blog, you can sponsor my open source work financially so I can write this blog and contribute to Free Software as my daily job.

Mount a folder on another folder

Written by Solène, on 22 May 2018.
Tags: #openbsd70 #openbsd

Comments on Fediverse/Mastodon

This article will explain quickly how to bind a folder to access it from another path. It can be useful to give access to a specific folder from a chroot without moving or duplicating the data into the chroot.

Real world example: “I want to be able to access my 100GB folder /home/my_data/ from my httpd web server chrooted in /var/www/”.

The trick on OpenBSD is to use NFS on localhost. It’s pretty simple.

# rcctl enable portmap nfsd mountd
# echo "/home/my_data -network= -mask=" > /etc/exports
# rcctl start portmap nfsd mountd

The order is really important. You can check that the folder is available through NFS with the following command:

$ showmount -e
Exports list on localhost:

If you don’t have any line after “Exports list on localhost:”, you should kill mountd with pkill -9 mountd and start mountd again. I experienced it twice when starting all the daemons from the same commands but I’m not able to reproduce it. By the way, mountd only supports reload.

If you modify /etc/exports, you only need to reload mountd using rcctl reload mountd.

Once you have check that everything was alright, you can mount the exported folder on another folder with the command:

# mount localhost:/home/my_data /var/www/htdocs/my_data

You can add -ro parameter in the /etc/exports file on the export line if you want it to be read-only where you mount it.

Note: On FreeBSD/DragonflyBSD, you can use mount_nullfs /from /to, there is no need to setup a local NFS server. And on Linux you can use mount --bind /from /to and some others ways that I won’t cover here.