FreeBSD and centOS commands and stuff

Edit user database information associated with user or, by default, the current user
fbsd = chapss
centos = usermod

Block a specific IP address
centos = iptables -I INPUT -s -j DROP

reload sshd after config change
fbsd = kill -HUP `cat /var/run/`
centos = service sshd reload

Drop to single user mode CentOS
Reboot machine.
At GRUB menu, hit any key.
Select with arrow keys
To enter edit mode type the character: a
Move to end of line, insert a space then type: single
Hit enter