efivarfs_set_variable: writing to fd 8 failed

[junky@mail.sheugh.com]

Dear Maintainer,

Subject: efivarfs_set_variable: writing to fd 8 failed
Package: shim-signed-common
Version: 1.33+15+1533136590.3beb971-7
Severity: normal

Dear Maintainer,

Grub threw an error message while apt was running an update: 
Setting up shim-signed-common (1.33+15+1533136590.3beb971-7) ...
Installing for x86_64-efi platform.
grub-install: warning: Cannot set EFI variable Boot0000.
grub-install: warning: efivarfs_set_variable: writing to fd 8 failed: No space left on device.
grub-install: warning: _efi_set_variable_mode: ops->set_variable() failed: No space left on device.
grub-install: error: failed to register the EFI boot entry: No space left on device.
dpkg: error processing package shim-signed-common (--configure):
 installed shim-signed-common package post-installation script subprocess returned error exit status 1
dpkg: dependency problems prevent configuration of shim-signed:amd64:
 shim-signed:amd64 depends on shim-signed-common (= 1.33+15+1533136590.3beb971-7); however:
  Package shim-signed-common is not configured yet.

I have an SSD and a 10Tb HGST hard drive

IIRC the boot sector is the first 1Gb sector on the hard drive

df says this: 
Filesystem      1K-blocks       Used  Available Use% Mounted on
udev             16426340          0   16426340   0% /dev
tmpfs             3296004       9684    3286320   1% /run
/dev/sda2       479567536    9352844  445784256   3% /
tmpfs            16480004          8   16479996   1% /dev/shm
tmpfs                5120          4       5116   1% /run/lock
tmpfs            16480004          0   16480004   0% /sys/fs/cgroup
/dev/sda1         9745696       5220    9740476   1% /boot/efi
/dev/sda4       960185376   12220944  899119940   2% /var
/dev/sda5      7265425656 1530107956 5369090348  23% /home
tmpfs             3296000          4    3295996   1% /run/user/111
tmpfs             3296000          0    3296000   0% /run/user/1000

-- System Information:
Debian Release: 10.2
  APT prefers stable
  APT policy: (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 4.9.0-8-amd64 (SMP w/12 CPU cores)
Kernel taint flags: TAINT_OOT_MODULE
Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8), LANGUAGE=en_GB:en (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages shim-signed-common depends on:
hi  debconf [debconf-2.0]  1.5.71
ii  mokutil                0.3.0+1538710437.fb6250f-1

shim-signed-common recommends no packages.

shim-signed-common suggests no packages.

-- debconf information:
  shim/secureboot_key: (password omitted)
  shim/secureboot_key_again: (password omitted)
  shim/error/bad_secureboot_key:
  shim/secureboot_explanation:
  shim/error/secureboot_key_mismatch:
  shim/title/secureboot:
  shim/disable_secureboot: true
  shim/enable_secureboot: false