Enable user authentication for single user mode

By default you will be automatically logged in to single user mode as root, this can be security risk so better to enable a user login add the single user mode

Note - Debian and therefore Ubuntu both require root password when booting into
single user mode or recovery mode. RHEL and CentOS allows access from the console
into single user mode without a password. This is handy when things get
messed up preventing access to the auth subsystems. To accomplish the
same behavior under Ubuntu, edit the /etc/inittab file and change the line

01. To edit this system file
#nano /etc/inittab

02. Go to a new line at the end of file then type
sum:S:wait:/sbin/sulogin

03. Save this file
Ctrl + O

04. Exit the file
Ctrl + X

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