My Fedora 27 writes actual data to USB on umount. Before umount it works only with links or something like that. So, for example, when I transfer a big file of 5 GB cp /home/iam/bigFile /run/mnt/iam/myUSB/ it will be transferred in several seconds. But there are no actual writes. After I use umount /dev/sdd1 it will be unmounting the USB for several minutes.
If I remove the USB after cp /home/iam/bigFile /run/mnt/iam/myUSB/ but before umount /dev/sdd1 the file will be corrupted.
How to force Fedora to write real data when I use cp?

  • I haven’t tried, but I wonder if mounting it with the sync flag would help.
    – Jeff Schaller
    Nov 23, 2017 at 17:25

1 Answer 1


After copying the files, run sudo sync -f one/of/the/files. It will write all the filesystem cached data where that file is stored immediately. Read the man page for some regards on file systems.

  • Is it possible to configure sync by default? So, that all data I place to flash drives are written immediately?
    – Oleksandr
    Nov 23, 2017 at 17:17
  • You'd need to mount it with a write through option. I can't look into the details right now, but you should be able to find it with a simple internet search...
    – Zip
    Nov 23, 2017 at 17:36
  • Oh, @Jeff Schaller seems to have commented just that on your question...
    – Zip
    Nov 23, 2017 at 17:37

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