$ unshare -rm bash -c "mount -t tmpfs tmpfs /proc && gnu-df ." ; echo $?
df: Warning: cannot read table of mounted file systems: No such file or directory
Filesystem     1K-blocks  Used Available Use% Mounted on
-                1970584 98352   1872232   5% /tmp
0
$ unshare -rm bash -c "mount -t tmpfs tmpfs /proc && uu-df ." ; echo $?
df: cannot read table of mounted file systems: No such file or directory
1