postinst is in tightvncserver 1.3.10-0ubuntu4.
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 27 28 | #!/bin/sh
set -e
if [ "$1" = "configure" ]; then
    MAN=/usr/share/man/man1
    BIN=/usr/bin
    update-alternatives --install \
	$BIN/vncserver       vncserver       $BIN/tightvncserver 70 \
	--slave \
	$MAN/vncserver.1.gz  vncserver.1.gz  $MAN/tightvncserver.1.gz \
	--slave \
	$BIN/vncconnect      vncconnect      $BIN/tightvncconnect \
	--slave \
	$MAN/vncconnect.1.gz vncconnect.1.gz $MAN/tightvncconnect.1.gz
    update-alternatives --install \
	$BIN/Xvnc            Xvnc            $BIN/Xtightvnc 70 \
	--slave \
	$MAN/Xvnc            Xvnc.1.gz       $MAN/Xtightvnc.1.gz
    update-alternatives --install \
        $BIN/vncpasswd      vncpasswd            $BIN/tightvncpasswd 70 \
        --slave \
        $MAN/vncpasswd.1.gz vncpasswd.1.gz       $MAN/tightvncpasswd.1.gz
fi
exit 0
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