mount --bind

https://bindfs.org/

bindfs

Mount a directory to another location and alter permission bits.

bindfs is a FUSE filesystem for mounting a directory to another location, similarly to mount --bind. The permissions inside the mountpoint can be altered using various rules.

Examples

Here are some examples of what bindfs can do for you:

• Make a directory read-only for non-root users.
  bindfs --perms=a-w somedir somedir

• Share a directory with some other users without modifying /etc/group.
  bindfs --mirror-only=joe,bob,@wheel ~/some/dir shared

• Make all new files uploaded to an FTP share owned by you and seen by everyone.
  bindfs --create-for-user=me --create-with-perms=u+rw,a+rD /var/ftp/uploads /var/ftp/uploads

• Make your website available to the webserver process read-only.
  bindfs --force-user=www --perms=0000:u=rD ~/stuff/website ~/public_html

• The corresponding /etc/fstab entry.
  /home/bob/stuff/website /home/bob/public_html fuse.bindfs force-user=www,perms=0000:u+rD 0 0