Just change their password to something unguessable with the passwd command.
The last answer to this was incorrect. Whether or not you are the only user on the system or not: Linux is always a multi-user operating system.
We can be asking after logging but we can answer even without logging in the user
The Linux administrator is called the "root" user.
With most Unix-derived systems, "root" is the super-user account.
No. Linux, like Unix, is designed to be a multi-user system.
Yes, as long as they have user accounts on both machines.
No. There is no single user interface for Linux. GNOME. KDE, Xfce, Fluxbox, and CDE are all examples of user interfaces / desktop environments for Linux.
There is no singular user interface for Linux. Linux itself makes no requirement for a user interface. There are plenty of interfaces: GNOME, KDE, Xfce, LXDE, BASH, ZSH, CSH, TSH, FISH, and dozens of window managers.
multi-user system
A Linux user can belong to multiple groups, and in most circumstances, it would be very difficult to utilize a Linux system without being so.
a user profile that prevents the user from logging on if the mandatory profile is unavailable
unix and linux systems are true multi user (root + others) but in windows admin and main user are same !