В Sun, 8 Dec 2013 20:27:33 +0400 Andrey Borzenkov <arvidjaar@gmail.com> пишет:
What happens here is - when filesystem is entered in /etc/fstab with "auto,nofail", systemd tries to mount this filesystem as soon as it sees device for it. Without "nofail" it would have failed on boot already. When filesystem is unmounted using GUI, device is deleted from system, so next time device appears it is attempted to be mounted.
This behavior is rather unexpected to me as well and seems new in systemd coming with 13.1. I cannot say whether this is intentional change or not.
Actually it seems to be present for quite some time. For filesystems with "auto" systemd implicitly adds Wants dependency from device to mount unit. Thinking about it, it does not sound that weird. You asked for device to be automatically mounted and it ensures it *is* automatically mounted as soon as it is present. Of course, this is one of many silent assumptions made by systemd which better be documented ...