Learn Linux: basic commands, file system, permissions, process management, networking, shell scripting, package management and server administration.
FHS hierarchy, rwx permissions, ownership and symlinks.
/etc, /var, /usr, /proc, /sys, /tmp and root structure.
chmod, chown, chgrp, umask, setuid/setgid/sticky.
Hard links, symlinks, find, locate, which, whereis.