postinst is in openjdk-6-jre-headless 6b31-1.13.3-1ubuntu1.
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 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 | #!/bin/sh
set -e
multiarch=x86_64-linux-gnu
priority=1061
basedir=/usr/lib/jvm/java-6-openjdk-amd64
mandir=$basedir/jre/man
srcext=1.gz
dstext=1.gz
jre_tools='java keytool pack200 rmid rmiregistry unpack200 orbd servertool tnameserv'
case "$1" in
configure)
    # fail early.  java currently uses tricks to find its own shared
    # libraries depending on the path of the binary. Will be changed
    # in OpenJDK7
    if ! mountpoint -q /proc; then
	echo >&2 "the java command requires a mounted proc fs (/proc)."
	exit 1
    fi
    [ -d /etc/.java ] || mkdir -m 755 /etc/.java
    [ -d /etc/.java/.systemPrefs ] || mkdir -m 755 /etc/.java/.systemPrefs
    if [ ! -f /etc/.java/.systemPrefs/.system.lock ]; then
	touch /etc/.java/.systemPrefs/.system.lock
	chmod 644 /etc/.java/.systemPrefs/.system.lock
    fi
    if [ ! -f /etc/.java/.systemPrefs/.systemRootModFile ]; then
	touch /etc/.java/.systemPrefs/.systemRootModFile
	chmod 644 /etc/.java/.systemPrefs/.systemRootModFile
    fi
    if [ -z "$2" ]; then
	update_alternatives=y
    fi
    if [ -n "$multiarch" ] && [ -n "$2" ]; then
	for i in $jre_tools; do
	    if [ -z "$(update-alternatives --list $i 2>/dev/null | grep ^$basedir/)" ]; then
		update_alternatives=y
		break
	    fi
	done
    fi
    if [ "$update_alternatives" = y ]; then
    if [ -n "$multiarch" ] && [ "$DPKG_MAINTSCRIPT_ARCH" != $(dpkg --print-architecture) ]; then
	priority=$(expr $priority - 1)
    fi
    for i in $jre_tools; do
	unset slave1 slave2 || true
        if [ -e $mandir/man1/$i.$srcext ]; then
	    slave1="--slave \
		/usr/share/man/man1/$i.$dstext \
                $i.$dstext \
                $mandir/man1/$i.$srcext"
	fi
	# disabled
        if false && [ -e $mandir/ja/man1/$i.$srcext ]; then
	    slave2="--slave \
		/usr/share/man/ja/man1/$i.$dstext \
                ${i}_ja.$dstext \
                $mandir/ja/man1/$i.$srcext"
	fi
        update-alternatives \
            --install \
            /usr/bin/$i \
            $i \
            $basedir/jre/bin/$i \
            $priority \
	    $slave1 $slave2
    done
    update-alternatives \
	--install /usr/bin/jexec jexec $basedir/jre/lib/jexec $priority \
	--slave \
	    /usr/share/binfmts/jar \
	    jexec-binfmt \
	    $basedir/jre/lib/jar.binfmt
    fi # update alternatives
    if [ -n "$multiarch" ] && [ -n "$2" ] && dpkg --compare-versions "$2" lt 6b23~pre9-1~; then
	for d in cmm; do
	    if [ -d $basedir/jre/lib/$d ] && [ ! -h $basedir/jre/lib/$d ]; then
		rm -rf $basedir/jre/lib/$d
		ln -s ../../../java-6-openjdk-common/jre/lib/$d $basedir/jre/lib/$d
	    fi
	done
    fi
    # register binfmt; ignore errors, the alternative may already be
    # registered by another JRE.
    if which update-binfmts >/dev/null && [ -r /usr/share/binfmts/jar ]; then
        update-binfmts --package openjdk-6 --import jar || true
    fi
    # activate class data sharing
    case amd64 in i386|sparc)
	rm -f $basedir/jre/lib/amd64/client/classes.jsa
	log=$(tempfile)
	if ! $basedir/bin/java -client -Xshare:dump -XX:PermSize=128m > $log; then
	    cat >&2 $log
	    rm -f $log
	    # this may fail on some machines/configurations, just ignore it.
	    echo >&2 "ignoring dump failure"
	    #exit 1
	fi
	rm -f $log
    esac
    case amd64 in amd64|i386|sparc)
	rm -f $basedir/jre/lib/amd64/server/classes.jsa
	log=$(tempfile)
	if ! $basedir/bin/java -server -Xshare:dump > $log; then
	    cat >&2 $log
	    rm -f $log
	    # this may fail on some machines/configurations, just ignore it.
	    echo >&2 "ignoring dump failure"
	    #exit 1
	fi
	rm -f $log
    esac
    # not shipped anymore
    rm -f /etc/openjdk-6/security/nss-*.cfg
    ;;
esac
exit 0
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