linuxexpert-practice-labs/labs/lfca/1-2-command-line/README.md

LFCA 1.2: Command line

Directories, finding files, reading the SSH log, permissions, archives, two editors, and a script of your own on the PATH.

Before you start

Work as root (sudo -i), so ~ is /root. Answers go in /root/lab-answers/<task>. The lab creates ~/editme.txt for task 6 and saves your ~/.bashrc and sshd's settings so reset can put them back. Files in /tmp don't survive a reboot, so do the tasks in one go and run le-lab check before you reboot.

Tasks

1. Make ~/practice/a/b with one command, move into b, and get back home three different ways.
2. Find every file under /etc whose name ends in .conf, save the list to ~/conf-files.txt, count its lines, and write the count to /root/lab-answers/2.
3. Make sure the SSH server is running and allows password logins (turn them on if not), run ssh localhost and type a wrong password. Count the failures in sshd's journal and write the count to /root/lab-answers/3.
4. Make a file /tmp/private.txt that only you can read and write, check it with ls -l, then create user bob with a home directory and try sudo -u bob cat /tmp/private.txt.
5. Archive ~/practice to ~/practice.tar.gz with tar -czf, delete ~/practice, and restore it from the archive.
6. Open ~/editme.txt in vi, change before to after on the first line, save and quit. Then do the same on the second line in nano (install it if it's missing).
7. Add ~/scripts to PATH in ~/.bashrc, put a script hello in it with a #!/bin/bash first line, make it executable with chmod u+x, and run it as hello in a new shell.

Hints

• mkdir -p, cd, cd ~, cd ../../.., cd - and pwd.
• find /etc -name '*.conf' > ~/conf-files.txt, wc -l.
• systemctl status sshd (ssh on Ubuntu). sshd -T | grep passwordauth should say yes; many cloud images set it to no, on Ubuntu in /etc/ssh/sshd_config.d/50-cloud-init.conf. Change it there and systemctl restart sshd (ssh on Ubuntu).
• journalctl -u sshd | grep -c "Failed password" (-u ssh on Ubuntu).
• chmod 600, useradd -m bob; the cat should fail.
• tar -czf ~/practice.tar.gz -C ~ practice, rm -r, tar -xzf, tar -tzf to look inside.
• vi: i to insert, Esc, :wq. nano: Ctrl-O to save, Ctrl-X to quit. dnf install nano on the RHEL family.
• export PATH="$HOME/scripts:$PATH" in ~/.bashrc, bash or a new login to get a new shell, type hello.