For Proxmox VE, the default login is User ID root, and the Installation time Password, for some reason, If the root password is forgotten, or not working then it can be reset using the following procedure:

Boot the Proxmox VE in Grub Edit mode by pressing e on the keyboard, this is shown in the screenshot.

Proxmox grub edit mode to reset default login detail.

In the Grub-edit mode scroll down to the highlighted line, and add the line: init=/bin/bash in the following manner as shown in the screenshots.

After adding the line press Ctrl x, this will boot the system in a Linux bash shell.

proxmox booting in the bash shell to reset default login details.

Next, type the following command:

mount -rw -o remount /
This will mount the root directory in read/write mode.

After this, type the new password using the following syntax. In case of multiple users, you may replace “root” with another user name.

passwd root “Enter New Password”

Next, enter the password again to confirm.

proxmox reset installation time root user password

Lastly, manually reboot your Proxmox VE Server, this will reset the default login password.