· about 5 minutes · runs on alpine, ubuntu-26.04, rocky-10 · unrated
An unrated lab. It runs on your machine with no account and no network, and everything about it — the faults, the checks, the hints and the reference solution — is in the repository. An attempt on it is recorded on your profile and never moves a rating: only rated labs do. Rated and unrated labs.
Welcome to Norboten. This machine is yours: break it, fix it, reset it.
Someone left a message for everyone who logs in, in /srv/hello/message.txt. When you try to read
it, you are refused.
reply.txt in your
home directory.When you think you are done, press c on this lab's screen. It grades the machine, reboots it,
and grades it again. Stuck? Select a check and press h.
The machine is checked, rebooted, and checked again. A check passes only if it passes both times.
| Check | Objective |
|---|---|
| 01_message_readable | Read file permissions and use sudo |
| 02_reply_written | Create a file with given contents |
Where the lab's hints send you, level by level, as you ask for them (h, then l opens a journal section in the TUI).
man 1 lsman 1 chmodman 1 cat3 questions on the same topic, in the lab's Theory tab. They never affect the lab's grade. Here they are, to answer in place:
A file has mode 0600 and belongs to root. Who can read it?
Only root
0600 is rw for the owner and nothing for group and others. root can read it both as the owner and because root bypasses permission checks; ordinary users cannot.
man 1 chmod
Which command adds read permission for "others" and leaves every other bit alone?
chmod o+r file
Symbolic mode changes only the bits named. A numeric mode replaces all of them (004 would remove the owner's access); a=r sets read-only for everyone; chown changes ownership.
man 1 chmod
As an ordinary user with sudo rights, which commands let you read a file only root can read?
sudo cat /srv/hello/message.txt, sudo less /srv/hello/message.txt — more than one answer
With sudo the reading program itself runs as root. With cat piped into sudo tee, and with sudo echo reading a redirection, your own shell opens the file — the unprivileged cat or the redirection — before sudo is involved, so access is denied.
man 8 sudo