A checksum file records what your files were when you trusted them, and sha256sum -c tells you later whether any of them changed. This set covers that workflow, the POSIX way to compare two digests, the older tools, and what a matching digest does and does not prove.
Each one is marked as you go, and the explanation arrives straight after, which is
the part worth reading.
4 questions, marked as you go.
Tasks
These need your own device. Run the command in Termux, then paste what it printed.
The marking looks at what the output means, so spacing, version numbers and
ordering do not matter. If you have not installed anything yet, the
lesson covers the setup.
Write a checksum file and verify against it
The hashtool.sh you finished is saved next to you. This creates a small file, writes a checksum file for it, then checks the file against that list. Paste the check output.
Run this in Termux
On your own device. Nothing on this page executes it. The command runs in
your terminal, and this box only reads what you paste back.
The check prints one line per file, naming the file and whether it matched.
the file matched its recorded digest
the check named the file
the script ran
What a good answer looks like
One line reading a.txt: OK. That is sha256sum reporting that the digest it just computed matches the one recorded in SUMS. The value of the exercise is the second half: change the file and run the check again and the same line reads a.txt: FAILED, and the command exits non-zero. A checksum proves the file has not changed since the digest was taken. It does not prove who took the digest, which is what a signature adds.
Marking your own work
Both halves of this are checked in your browser, with no server involved, so nothing
stops you from pasting output you did not run. The tasks are written so that the
easiest way to pass one is to actually do it and read the result, which is the whole
intention.