A duplicate bind mounted directory (as opposed to a device) on which.The original namespace hidden (no more files could be opened, the problem can't get worse).Sudo mount -o bind,ro '$null_dir' '$original' Sudo mount -make-private '$original_duplicate' # Don't propagate/mirror the empty directory just about hide the original Sudo mount -o bind,ro '$original' '$original_duplicate' # So, avoid remount, and bind mount instead: # still files open for writing on the original as each mounted instance is # A request to remount,ro will fail on a `-o bind,ro` duplicate if there are Here's how: null_dir=$(sudo mktemp -directory -tmpdir empty.XXXXX') Hide the original mount point and block the namespace:.Temporarily duplicate the mountpoint with mount -o bind /media/hdd /mnt to another location.Why not use use fuser earlier? Well, you could have, but fuser operates upon a directory, not a device, so if you wanted to remove the mountpoint from the file name space and still use fuser, you'd need to: Read-only re-mount achievement unlocked рџ”“в‘Д¬ongratulations, your data on the mountpoint is now consistent and protected from future writing. If you can't remount read-only at this point, investigate some of the other possible causes listed here. You should then be able to remount the device read-only and ensure a consistent state. If you are unlucky, focus only on processes with files open for writing: lsof +f - /dev/ | awk 'NR=1 || $4~/+/'

Mount -o remount,ro /dev/device is guaranteed to fail if there are files open for writing, so try that straight up. The data is in a consistent state, should you need to physcially disconnect the device.All pending data has been written to disk.When you gain the remount,ro badge, you know that: The major unmount achievement to be unlocked is the read-only remount. Then any new accesses to filenames in the below the mountpoint will hit the newly overlaid directory with zero permissions - new blockers to the unmount are thereby prevented. This same behaviour can be achieved by mounting an empty directory with permissions 000 over the directory to be unmounted. The useful behaviour of umount -l is hiding the filesystem from access by absolute pathnames, thereby minimising further moutpoint usage. It can cause btrfs filesystem corruption.It doesn't actually unmount the device, it just removes the filesystem from the namespace.Umount -l is dangerous or at best unsafe. At the time of writing, the top-voted answer recommends using umount -l.

Mac could not unmount for repair