I read that to transfer an iso image to a pendrive and print progress I should execute pipeline below.
$ dd if=$IMG bs=4M | pv -s 668M | sudo dd of=/dev/sdc bs=4M
pv should print and update a progress bar in terminal. However, my progress bar jumped to 100% and the command hanged. I could not kill the dd writing to the pendrive so I looked under the hood.
journal
Jan 13 01:57:32 nixos systemd[1]: systemd-udevd.service: Watchdog timeout (limit 3min)!
Jan 13 01:57:32 nixos systemd[1]: systemd-udevd.service: Killing process 1830 (systemd-udevd) with signal SIGABRT.
Jan 13 01:57:54 nixos sudo[3787]: pam_unix(sudo:session): session closed for user root
Jan 13 01:57:54 nixos kernel: sdc: sdc1 sdc2
iotop
TID PRIO USER DISK READ DISK WRITE SWAPIN IO> COMMAND
1830 be/4 root 0.00 B/s 0.00 B/s 0.00 % 99.99 % systemd-udevd
3788 be/4 root 0.00 B/s 0.00 B/s 0.00 % 99.99 % dd of=/dev/sdc bs=4M
8 be/4 root 0.00 B/s 0.00 B/s 0.00 % 99.99 % [kworker/u64:0+flush-8:32]
I tried with sudo or as root. Same effect. pv shows 100% immediately but dd of=... blocks for about 3 minutes. That is not consistent with what I read on the internet and saw myself on other machines. What happened?
PS.
$ sudo hdparm -W /dev/sdc
/dev/sdc:
write-caching = not supported
PPS.
Tried status=progress - same effect (100% and hangs until write is complete).
sudo sh -c 'pv >/dev/sdc' <"$IMG". More efficient and less prone to short reads on the pipe causing a mis-write – Chris Davies Jan 17 '22 at 23:58pv -petrab file > destination. No need to pipe twice and use three commands instead of one. Also, just alsoddcan actually slow down things. – Artem S. Tashkinov Jan 18 '22 at 01:19