"Someone else has pirated this, so it's OK for me to do it as well" isn't a good argument.

If you see litter on the ground already, that doesn't make it OK to litter more.

It's also freely available from https://kea.nu/files/textbooks/humblesec/linuxbasicsforhacke... and plenty other places with a quick search.

first edition is also available on Internet Archive in multiple formats