Advanced Exercises

Give the command

$ /sbin/fuser -uv /

What is this a list of? Why is it so long? Give the same command as root (or ask the system administrator to do so and email you the results). How does this list differ from the first? Why is it different?

When it puts files in a lost+found directory, fsck has lost the directory information for the files and thus has lost the names of the files. Each file is given a new name, which is the same as the inode number for the file:

$ ls lg lost+found
rwrr 1 alex pubs   110 Jun 10 10:55 51262

What can you do to identify these files and restore them?

Take a look at /usr/bin/lesspipe.sh. Explain what it does and six ways it works.

Why are setuid shell scripts inherently unsafe?

When a user logs in, you would like the system to first check the local /etc/passwd file for a username and then check NIS. How do you implement this strategy?

Some older kernels contain a vulnerability that allows a local user to gain root privileges. Explain how this kind of vulnerability negates the value of a chroot jail.