Failure of rsync of multi-user directory with sshfs fuse mount

Question

I use rsync for automatic periodic syncing of the home folder (root user) in a linux server that is used by several people. A service that users need is the possibility of mounting remote directories through sshfs. However, when there is an sshfs mount, rsync fails giving the following messages

rsync: readlink_stat("/home/???/???") failed: Permission denied (13)
IO error encountered -- skipping file deletion
...
rsync error: some files/attrs were not transferred (see previous errors) (code 23) at main.c(1183) [sender=3.1.1]

Because of this error, the automated sync does not work as expected, in particular due to skipping the file deletion and a non-zero exit code. The sync is only necessary for the file system where home is mounted, so the wanted behavior is that the sshfs mounts be ignored. The -x / --one-file-system rsync option does not resolve it.

This problem is clearly explained in https://www.agwa.name/blog/post/how_fuse_can_break_rsync_backups . The follow-up article (https://www.agwa.name/blog/post/easily_running_fuse_in_an_isolated_mount_namespace) proposes a solution, though not an acceptable one because fuse mounts are only visible to the process created the mount.

I am looking for a solution that does not affect sshfs usability and is transparent for the users.

Answer 1

This error does not appear if the fuse mount points are excluded in the rsync command. Since it is an automated sync, the mount command can be used to obtain all fuse mount points. The output of the mount command may differ depending on the system, but in a debian jessie sshfs mounts appear as USER@HOST:MOUNTED_DIR on /path/to/mount/point type fuse.sshfs (rw,...). A simple way to automate the exclusion of fuse mounts in bash+sed is the following

SOURCE="/home/"

FUSEEXCLUDE=( $( mount |
  sed -rn "
    / type fuse/ {
      s|^[^ ]+ on ([^ ]+) type fuse.+|\1|;
      /^${SOURCE//\//\\\/}.+/ {
        s|^${SOURCE//\//\\\/}| --exclude |;
        p;
      }
    }" ) )

rsync $OPTIONS "${FUSEEXCLUDE[@]}" "$SOURCE" "$TARGET"