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.
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
/home/bob/stuff/website /home/bob/public_html fuse.bindfs force-user=www,perms=0000:u+rD 0 0
bindfs is available through the software repositories of many Linux distributions, as well as MacPorts on OS X. Check there first unless there is a specific new feature that you need.
Download the latest source tarball here: bindfs-1.13.10.tar.gz.
Compile & install:
./configure && make && sudo make install.
There is an extensive HowTo on Ubuntu Forums.
All FUSE filesystems necessarily incur a performance penalty in CPU time and memory consumption. If all you need is to make a directory read-only then
mount --bind -r is more efficient.
bindfs was initially developed in 2006. I consider the program fairly feature-complete but I’ll still gladly fix bugs and add some small features as people suggest them.