On 8/25/21 9:26 PM, Samuel Sieb wrote:
You could add a "sync" after the copy and before the
"umount".
https://utcc.utoronto.ca/~cks/space/blog/unix/TheLegendOfSync
We're getting into myths and legends territory. Running sync before
umount isn't harmful, but umount will flush any dirty buffers, so it
isn't necessary.
I'm not able to reproduce the problem described, though I'm running
Fedora 34. When I attach a USB drive, it is mounted with the "flush"
option. I can copy arbitrarily large file sets to the drive, and the
"cp" command appears to be nearly synchronous. The sequence "time cp
... ; time umount ..." indicates nearly all of the time spent is in the
cp command and umount requires between .2 and .3 seconds.
What are the indications that the copy operation originally reported was
incomplete? Does the "umount" command have any flags? Are there any
errors in "dmesg" after the script runs?