Error — failed to open /etc/webmin/authentic-theme/manifest-webmin.json for writing : no space left on device

Operating system: Ubuntu
OS version: 16.04 LTS

I cannot use the Virtualmin on my server.
I get the error:

ERROR — FAILED TO OPEN /ETC/WEBMIN/AUTHENTIC-THEME/MANIFEST-WEBMIN.JSON FOR WRITING : NO SPACE LEFT ON DEVICE

CALL STACK TRACE
|FILE|LINE|FUNCTION|
|---|---|---|
|/usr/share/webmin/web-lib-funcs.pl|9415|WebminCore::error|
|/usr/share/webmin/web-lib-funcs.pl|10519|WebminCore::open_tempfile|
|/usr/share/webmin/authentic-theme/authentic-init.pl|165|WebminCore::write_file_contents|
|/usr/share/webmin/authentic-theme/authentic-init.pl|183|WebminCore::embed_favicon|
|/usr/share/webmin/authentic-theme/authentic.pl|49|WebminCore::embed_header|
|/usr/share/webmin/web-lib-funcs.pl|1018|WebminCore::theme_header|
|/usr/share/webmin/authentic-theme/authentic-lib.pl|33|WebminCore::header|
|/usr/share/webmin/authentic-theme/index.cgi|12|main::authentic|
|(eval 280)|6|(eval)|
|/usr/share/webmin/miniserv.pl|2592|(eval)|
|/usr/share/webmin/miniserv.pl|1007|miniserv::handle_request|

while df -h shows there is no 100% Used on any mounted partition/lvm

post df -h results here.

Filesystem            Size  Used Avail Use% Mounted on
udev                   16G     0   16G   0% /dev
tmpfs                 3.2G   90M  3.1G   3% /run
/dev/mapper/vg-slash   25G   20G  3.7G  85% /
/dev/vg/usr           9.8G  2.5G  6.8G  27% /usr
tmpfs                  16G  4.0K   16G   1% /dev/shm
tmpfs                 5.0M     0  5.0M   0% /run/lock
tmpfs                  16G     0   16G   0% /sys/fs/cgroup
/dev/md1              2.0G  141M  1.7G   8% /boot
/dev/mapper/vg-var     49G   30G   17G  65% /var
/dev/mapper/vg-tmp     22G   23M   21G   1% /tmp
/dev/mapper/vg-home   325G  241G   69G  78% /home
/dev/loop0             11M   11M     0 100% /snap/canonical-livepatch/114
/dev/loop1             11M   11M     0 100% /snap/canonical-livepatch/105
/dev/loop2            100M  100M     0 100% /snap/core/11993
/dev/loop3            100M  100M     0 100% /snap/core/11798

Next release of Webmin 1.983+ will be resilient to out-of disk space issue upon initial load , which would let a user log in and fix a problem using UI.