rsync

Last updated on 2026-10-27 | Edit this page

Estimated time: 25 minutes

Overview

Questions

  • Which flags let a stopped copy continue?
  • What does cmp print when the two files match?

Objectives

  • Copy with rsync -a --partial and read one progress line from --info=progress2.
  • Use a trailing slash on the source so the contents arrive, with no extra directory level.
  • Stop one rsync with timeout, run it again, and check the bytes with cmp.

One careful copy

-a keeps links, times, and permissions. --partial leaves a broken file in place so the next run continues. --info=progress2 is one progress line for the whole transfer. --checksum reads every byte when size and time are not enough. A trailing slash on the source copies the contents, and it does not add an extra directory level.

Resume by running the same command again:

BASH 

rsync -a --partial \
  --info=progress2 \
  run/ /scratch-shared/$USER/run/

When size and time are not enough, add --checksum:

BASH 

rsync -a --checksum --partial \
  run/ /scratch-shared/$USER/run/

run/ with the slash fills /scratch-shared/$USER/run/ with the contents of run. The same source without the slash copies the directory as well, so the files sit at run/run/.

Catch it midway

Predict a short part/big.bin after timeout, then equal sizes. --bwlimit slows the first copy so two seconds is enough to stop it. --partial keeps the broken file, and the next rsync continues.

cmp exits 0 when the bytes match, and it prints nothing.

dd with bs=1M count=48 writes 48 MiB, which is 50331648 bytes. That is the size of big.bin. The partial file is shorter. On the ext4 example from 26 October 2026 it was 4128768 bytes of 50331648. Your byte count after two seconds can differ. The check is that the first ls shows a short file, the second rsync finishes the copy, and cmp is silent.

BASH 

dd if=/dev/zero of=big.bin bs=1M count=48
mkdir -p part
timeout 2 rsync -a --partial \
  --bwlimit=2000 big.bin part/
ls -l big.bin part/big.bin
rsync -a --partial big.bin part/
cmp big.bin part/big.bin

timeout stops the first rsync. That line is the interrupted copy. Continue with ls.

Challenge

Predict the two sizes

You run the block above. After timeout, how does part/big.bin compare with big.bin? After the second rsync, what does cmp print, and what is its exit status?

After timeout, part/big.bin is shorter than big.bin. big.bin is 50331648 bytes. On the ext4 run of 26 October 2026 the partial file was 4128768 bytes. After the second rsync the sizes match. cmp big.bin part/big.bin prints nothing and exits 0.

Challenge

Resume it

In an empty directory, run the six commands from this episode. Record the two sizes from the first ls -l, then run cmp and record its exit status with echo $?.

The first size column for part/big.bin is smaller than 50331648. The ext4 reference is 4128768 bytes. The second rsync makes the sizes equal. cmp prints nothing. echo $? prints 0.

Key Points
  • -a keeps links, times, and permissions. --partial keeps a broken file for the next run.
  • --info=progress2 is one progress line. --checksum reads every byte.
  • A trailing slash on the source copies the contents.
  • timeout 2 with --bwlimit=2000 leaves a short part/big.bin. The next rsync finishes it.
  • cmp prints nothing and exits 0 when the bytes match.