replace prior 18.04 installation with 21.04 (no format of partition sda1)

This bug has been reported on the Ubuntu ISO testing tracker.

A list of all reports related to this bug can be found here:
http://iso.qa.ubuntu.com/qatracker/reports/bugs/1923134

It seems you've run out of space.

Apr 9 06:36:06 ubuntu grub-installer: info: Identified partition label for /dev/sda1: msdos
Apr 9 06:36:07 ubuntu grub-installer: info: Installing grub on '/dev/sda'
Apr 9 06:36:07 ubuntu grub-installer: info: grub-install does not support --no-floppy
Apr 9 06:36:07 ubuntu grub-installer: info: Running chroot /target grub-install --force --target x86_64-efi "/dev/sda"
Apr 9 06:36:07 ubuntu grub-installer: Installing for x86_64-efi platform.
Apr 9 06:36:19 ubuntu systemd[1]: zsysd.service: Succeeded.
Apr 9 06:36:21 ubuntu grub-installer: grub-install: error: cannot copy `/usr/lib/grub/x86_64-efi-signed/grubx64.efi.signed' to `/boot/efi/EFI/ubuntu/grubx64.efi': No space left on device.
Apr 9 06:36:21 ubuntu grub-installer: error: Running 'grub-install --force --target x86_64-efi "/dev/sda"' failed.

Out of space? I'm confused

About half the disk space has been used (658GB) & about 3% of inodes are used (`df -hi`) on the single partition /dev/sda1

The box is BIOS (not efi) so no EFI partition is used, so /boot is on sda1

Re-attempted install.

Same sda1 partition used (except it's now a Lubuntu hirsute instead of bionic).

Refer new bug report https://bugs.launchpad.net/ubuntu/+source/ubiquity/+bug/1923680 I've marked as duplicate.

The 'out of space' issue I believe is because grub is being written to the installation-media (thumb-drive) and not disk

from other report

ubuntu@ubuntu:/$ df -h |grep target
/dev/sda1 658G 328G 297G 53% /target
/dev/sdb2 4.9M 4.9M 2.0K 100% /target/boot/efi

sdb2 is the installation media; sda is the drive install is being attempted on.

attempted install again to
- dell [optiplex] 780 (c2q-q9400, 8gb, amd/ati cedar radeon hd 5000/6000/7350/8350)

identical install to sda1; but ISO written this time with `sudo dd bs=4M oflag=sync status=progress of=/dev/sdb if=/de2900/ubuntu_64/hirsute-desktop-amd64.iso`

https://bugs.launchpad.net/ubuntu/+source/ubiquity/+bug/1923690

I wondering if my last comment was missing the /target/boot/efi reason for mount; is it trying to copy from there?? and not to there...

it's clear during install the partition is /dev/sda and boot loader was being written to sda on the dialog screens

--messages--
Apr 14 01:33:23 ubuntu grub-installer: info: Running chroot /target grub-install --force --target x86_64-efi "/dev/sda"
Apr 14 01:33:23 ubuntu grub-installer: Installing for x86_64-efi platform.
Apr 14 01:33:35 ubuntu grub-installer: grub-install: error: cannot copy `/usr/lib/grub/x86_64-efi-signed/grubx64.efi.signed' to `/boot/efi/EFI/ubuntu/grubx64.efi': No space left on device.
Apr 14 01:33:35 ubuntu grub-installer: error: Running 'grub-install --force --target x86_64-efi "/dev/sda"' failed.

so identical to bdmurray's comment; but disk space used is only at 53% and 3% inodes used on sda1 (only system partition being used).

ubuntu@ubuntu:/$ df -h |grep target
/dev/sda1 658G 328G 297G 53% /target
/dev/sdb2 4.9M 4.9M 2.0K 100% /target/boot/efi

just as last time.. but is it trying to write to sdb2?? which would explain the messages (though they say sda correctly)
there is plenty of disk space (297GB)

Likely related to https://bugs.launchpad.net/ubuntu/+source/ubiquity/+bug/1893964