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Say I have a folder which is completely readable by my user. I want it to be mounted to my home folder. I can't use a symlink because I want the files to be exposed at ~/ and I want other programs "not to know" that it's a mount. Is there a fuse program that implements this? The issue with mount is that it requires root privileges.

I'd also appreciate, if I'd be able to mount this directory, not on boot, but on demand - that's because my ~/ is encrypted unless I'm logged in.

Doron Behar
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    `fstab` can have a 'user' option specified on a particular mount. If you set this up once, you can then mount/unmount without being root. Is this an acceptable solution for you? – Haxiel Aug 02 '20 at 13:40
  • @Haxiel the answer I already got seems mostly satisfying, but your alternative seems interesting but I'm not sure I fully understand it although I read the relevant manpages. I tried to do something but I got errors on boot. Would it be possible to get an full answer with an fstab entry example? – Doron Behar Aug 10 '20 at 20:15
  • @Haxiel I've also edited the question - I'd like to mount this directory on demand and not on boot. – Doron Behar Aug 10 '20 at 20:17

2 Answers2

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Various FUSE utilities can do that. For instance, bindfs can mount a directory to a different location, similarly to what mount --bind would do.

bindfs --no-allow-other /source/directory /mount/point

The --no-allow-other option is needed unless you uncomment user_allow_other in /etc/fuse.conf (but see, below, the note about libfuse for the security implications).

Unmount with:

fusermount -u /mount/point

Note that FUSE file systems currently have known issues/limitations. It's worth mentioning, among other things, the performance cost, the impossibillity to use inotify to monitor file system events occurring on the source file system and the security implications listed in the libfuse GitHub repository's README.

On Linux, a bind mount performed as mount --bind would not have these downsides. But it would require root privileges at least once, to edit your fstab.
Refer to the linked Q/A for a much more detailed coverage of the subject.

fra-san
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3

You could set up /etc/fstab once, with the following entry:

/path/to/original/dir  /path/to/bind/dir  none  bind,rw,user,noauto  0 0

The mount options specify the following things, in order:

  • bind indicates that this entry is a bind mount.
  • rw specifies that the entry will be mounted in read-write mode.
  • user allows any non-root user to mount the filesystem.
  • noauto specifies that this entry should not be automatically mounted with mount -a and at boot time.

You'll need to set this up once using root privileges. Once the entry is in place, you can perform the mount as a non-root user. Simply run mount /path/to/bind/dir.

A couple of points to note:

  • With the user option, only the same user account that originally mounted the filesystem can perform the unmount. If multiple users are involved, you can look at the users option instead. See man 8 mount for details.
  • The user option implies three other options: noexec (do not permit execution of binaries), nosuid (do not honor setuid/setgid bits) and nodev (do not interpret devices). If you want to restore any of these functionality, append the corresponding option to the end of the list. For example, bind,rw,user,noauto,exec. Keep in mind that there are security implications for these options. See man 8 mount for details.
fra-san
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Haxiel
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  • that sounds great but I'm getting this error when I mount without root: `mount: /home/doron/repos: must be superuser to use mount.`. I've added this line to my fstab: `/var/src /home/doron/repos none bind,rw,user,noauto 0 0`. – Doron Behar Aug 11 '20 at 21:44
  • @DoronBehar That's a bit strange, because the configuration works on my Fedora system. Can you check if you have more than one entry for '/home/doron/repos' in the `fstab` file? – Haxiel Aug 12 '20 at 03:39
  • Definitely it is the only line with `/var/src` and `/home/doron/repos`. I've also tried to test whether it'll work only if `/var/src` has my _full_ permissions, and I'm the owner of, and that didn't work either, failing the same way :/. – Doron Behar Aug 12 '20 at 07:12
  • Is it possible that you have modified the permissions on the `mount` binary itself? I found a discussion [here](https://www.linuxquestions.org/questions/slackware-14/must-be-superuser-to-use-mount-fstab-is-correct-however-144932/) that may be helpful. – Haxiel Aug 12 '20 at 15:27
  • It worked! Thanks again @Haxiel for the dedication, deeply appreciated. – Doron Behar Aug 12 '20 at 20:23