User Management

Rename User

Rename the user from foo to bar:

# usermod -l bar foo

Rename the group from foo to bar:

# groupmod -n bar foo

Rename user home directory:

usermod -d /home/bar -m bar

Add a system user and group

adduser --system --home /opt/USER --shell /bin/bash --group GROUP USER

Run command as an "ordinary" user

# runuser -u USER -- command arg1 arg2

# sudo -u USER [-g GROUP] command arg1 arg2

Reset root Password (GRUB)

Start the machine and press any key to stop the boot process.

Press [e] on GRUB menu to edit boot command line parameters.

Specify bash as init: find the line with kernel parameters (starts with linux) and add init=/bin/bash (use arrows, [Home] and [End] for navigation).

Press [Ctrl] + [x] or [F10] to boot.

The system will boot into single user mode with the root filesystem mounted as read-only. Re-mount it in r+w mode:

mount -n -o remount,rw /

Now, change the password

passwd

and reboot.

Alternatively if using systemd, add systemd.debug-shell=1 parameter and switch to 9-th console after boot (no need to remount anything).