• Restart your vCenter appliance and wait for the Photon OS Splash screen during boot.

• Once booted hit the letter e to enter the boot menu.
• Change to the GNU GRUB boot menu editor and hit enter.

• Add the following string behind the line that starts with linux: rw init=/bin/bash

• Hit the F10 function key to boot the changed entry.

How to clean up the root partition

Check the root partition usage, using the df -h command. Very often the log files grew large and filled up your partition.

check the usage of  audit.log in /var/log/audit by follwoing commad

ls -sh /var/log/audit

To remove the file follow this

rm /var/log/audit/*.log to clean it up.

How to reset the root password

Please follow these steps:

passwd 

Enter a strong password twice and make sure you will remember same for future

umount /

reboot -f