ltsp-build-client Error on Linux Mint 19

[mherweg]

I got this error:

Setting up ldm-ubuntu-theme (2:2.0.47) ...
update-alternatives: using /usr/share/ldm/themes/ubuntu to provide /usr/share/ldm/themes/default (ldm-theme) in auto mode
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package ldm-mint-theme is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
However the following packages replace it:
  mint-artwork

Package mint-artwork-common is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
However the following packages replace it:
  ubuntu-system-adjustments mint-artwork

E: Package 'mint-artwork-common' has no installation candidate
E: Package 'ldm-mint-theme' has no installation candidate
error: LTSP client installation ended abnormally

I tried to fix it by changing a line in the file:
/usr/share/ltsp/plugins/ltsp-build-client/Ubuntu/001-set-mint-dist

Before:
LATE_PACKAGES="linuxmint-keyring mint-meta-core mint-artwork-common ldm-mint-theme $LATE_PACKAGES"

after:
LATE_PACKAGES="linuxmint-keyring mint-meta-core mint-artwork ldm-ubuntu-theme libglib2.0-0 libglib2.0-bin $LATE_PACKAGES"

Then I get this Error:

setting up mintinstall
error: GPG signatures found but none are in trusted keyrings

Is there a way to speed up the debugging process?
download & install of all those packages takes 20 minutes each time.

[mherweg (m-herweg)]

SOLVED:

It works now with --accept-unsigned-packages

[mherweg (m-herweg)]

...AND my changed

/usr/share/ltsp/plugins/ltsp-build-client/Ubuntu/001-set-mint-dist

file.

[Alkis Georgopoulos (alkisg)]

Closing old LTSP bugs as they're no longer relevant after LTSP has been rewritten from scratch.