postinst is in novnc 1:0.4+dfsg+1+20131010+gitf68af8af3d-7.
This file is a maintainer script. It is executed when installing (*inst) or removing (*rm) the package.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 | #!/bin/sh
set -e
pkgos_adduser () {
	local VAR_UG_PKG_NAME
	VAR_UG_PKG_NAME=${1}
	# Create user and groups if they don't exist
	if ! getent group ${VAR_UG_PKG_NAME} > /dev/null 2>&1 ; then
		addgroup --quiet --system ${VAR_UG_PKG_NAME}
	fi
	if ! getent passwd ${VAR_UG_PKG_NAME} > /dev/null 2>&1 ; then
		adduser --system \
			--home /var/lib/${VAR_UG_PKG_NAME} \
			--no-create-home \
			--quiet \
			--disabled-password \
			--shell /bin/bash \
			--group ${VAR_UG_PKG_NAME}
	fi
}
if [ "$1" = "configure" ]; then
	pkgos_adduser nova
fi
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