/usr/lib/tasksel/info/desktop.preinst is in tasksel-data 2.88ubuntu15.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 | #!/bin/sh
set -e
# We install the X server early on so that other packages (e.g. usplash) can
# get at the resolution it configures. It is listed as part of the task,
# which will take care of its removal when the task is removed.
for pkg in xserver-xorg; do
if apt-cache show "$pkg" >/dev/null 2>&1 &&
! dpkg --get-selections | egrep "^$pkg[[:space:]]+install"; then
apt-get "$@" -q -y -f install $pkg >/dev/null || true
fi
done
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