On Sun 06 May 2018 at 15:53:05 +1200, Richard Hector wrote: > On 06/05/18 07:35, Brian wrote: > > On Sat 05 May 2018 at 11:06:25 -0500, Richard Owlett wrote: > > > >> What are the distinguishing features of unmount, Safely Remove Drive, and > >> Eject? > > > > There are none. The device is either unmounted or it isn't. It cannnot > > be half-unmounted. > > Hmm. Is there not a point where it's been made inaccessible to the > filesystem, but caches are not yet flushed?
I don't know but I've always thought that unmounting a USB stick led to a sync action and buffers were flushed. Anyway, in the light of Henrique de Moraes Holschuh's enlightening post I'll back away a little from my previous mail and give a restructured response. Although it is from a few years ago, the material at https://bugzilla.gnome.org/show_bug.cgi?id=598690 could still be useful. Safely Remove Drive and Eject are associated with DEs, although Xfce seems to manage without them and has unmount as an only option. udisks2 is the software involved. A test (as an unprivileged user) after plugging in a USB stick: lsblk (To get the device) udisksctl mount -b /dev/sdg1 udisksctl unmount -b /dev/sdg1 (Must be done before the next command). udisksctl power-off -b /dev/sdg1 (Observe indicator light on the stick). The stick needs detaching and re-inserting to get mounting to work again. >From udisksctl(1): power-off Arranges for the drive to be safely removed and powered off. On the OS side this includes ensuring that no process is using the drive, then requesting that in-flight buffers and caches are committed to stable storage. The exact steps for powering off the drive depends on the drive itself and the interconnect used. For drives connected through USB, the effect is that the USB device will be deconfigured followed by disabling the upstream hub port it is connected to. Note that as some physical devices contain multiple drives (for example 4-in-1 flash card reader USB devices) powering off one drive may affect other drives. As such there are not a lot of guarantees associated with performing this action. Usually the effect is that the drive disappears as if it was unplugged. I'm still pondering why I would need power-off with a USB device. -- Brian.
