Stephen Harris wrote:
And, remember, that the output of "df" might have changed in between times you ran "df" and you ran the "awk" command; there's only 7Mbytes difference. Did someone delete a 7Mbyte file? Send email? Finish a print job? Or... could be plenty of reasons for the used amount to go down.
The awk script works correctly, as can be tested easily:
$ cat h Filesystem 1024-blocks Used Available Capacity Mounted on /dev/mapper/VolGroup00-LogVol00 274405432 18584656 241656808 8% / /dev/sda2 101105 19096 76788 20% /boot tmpfs 1682508 0 1682508 0% /dev/shm
$ cat h | awk '/^/dev// { avail += $3/1024 } END { printf("%d Mb used\n",avail)}' 18167 Mb used
But the whole system used only 18 MB ? That's not true.