ln -s vs mount --bind

First ,Symlinks and bind mounts are a whole different ballgame.

ln -s you create a symbolic link,which is an inode pointing to a certain filesystem object.

If you mount a filesystem with --bind, you create a second mountpoint for a device or filesystem.

If you envision a symlink as a redirect, then envision a --bind mounted filesystem as creating another gateway to data.

The --bind mount seems a bit more robust to me and it probably is a bit faster than working with a symlink.

a symlink is visible in an ls,whereas a bind mount is only visible when looking at /proc/mounts or /etc/mtab (which is what the mount command does, if it is executed without parameters).

 

One of the big differences between ln -s and a bind mount is that you can use a bind mount to "modify" a read-only filesystem.

For example, if there were a CD mounted on /mnt/application, and you wanted to replace /mnt/application/badconfigfile.conf with a correct version, you could do this:

mount -o bind /path/to/correct/file.conf /mnt/application/badconfigfile.conf

It would not be possible to affect the same change using a symlink because you're not able to modify the target filesystem. This can also be used to good affect if you distributed a common suite of software via NFS (or some sort of cluster filesystem), and you want to make host-specific changes on one system. You can simply use a bind mount on the target system to override the files or directories as necessary.

 

Practial difference #1 for me between ln -s and mount --bind :

vsftpd doesn't not allow to browse a directory through a symbolic link, but allows when mounted

 

One might note that as a consequence of binding to a mount, which is itself a binding, that is later rebound, the original binding remains intact, assuming everything physically stay connected.

That is, if bind A to B and bind B to C, and then bind D to B, C will still be bound to A. That might be what you want, or not. If one desires C to follow B then remount using the same targets, i.e. mount -o remount B C, or use --rbind instead. There is no --rebind option.

 

 

 

mount, when invoked without any arguments, prints the contents of /etc/mtab, which has slightly different information than /proc/mounts. (In particular, /proc/mounts (symlink to /proc/self/mounts) always shows the mountpoints visible to the process reading it.) –