linuxexpert-practice-labs/labs/linux-plus/2-1-2-finding-files-links-devices/README.md

Linux+ 2.1.2: Finding files, links and device files

Finding files by size and permission, the locate database, hard and symbolic links, and finding which process holds a file open.

Before you start

Work as root. The lab installs plocate and lsof, leaves a large file and an extra set-user-ID program somewhere on the root filesystem, and starts a process that keeps /tmp/held.txt open. Write answers to the files in /root/lab-answers/. Don't run the chapter's final clean-up (rm -f ... /tmp/h.txt /tmp/s.txt ~/findme-*.txt): the lab grades those files, and le-lab reset removes them.

Tasks

1. Find every regular file over 50 MiB and every set-user-ID file on the root filesystem (don't cross into other filesystems). Save their full paths, one per line, in /root/lab-answers/1 (ls -l style lines are fine too).
2. Create a file ~/findme-<something>.txt, then make locate findme- find it.
3. In /tmp, create t.txt containing hi, a hard link h.txt to it and a symbolic link s.txt to it. Then delete t.txt, and see which of the two links still works.
4. Find the process that holds /tmp/held.txt open, and write its PID to /root/lab-answers/4.

Hints

• find / -xdev -type f -size +50M, find / -xdev -perm -4000 -type f, 2>/dev/null.
• locate only knows what the last updatedb saw.
• ln, ln -s, ls -li.
• lsof /tmp/held.txt, or fuser.