/etc/ca-certificates/update.d/jks-keystore is in ca-certificates-java 20160321.
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 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  | #!/bin/sh
set -e
# use the locale C.UTF-8
unset LC_ALL
LC_CTYPE=C.UTF-8
export LC_CTYPE
storepass='changeit'
if [ -f /etc/default/cacerts ]; then
    . /etc/default/cacerts
fi
arch=`dpkg --print-architecture`
JAR=/usr/share/ca-certificates-java/ca-certificates-java.jar
nsslib_name()
{
    if dpkg --assert-multi-arch 2>/dev/null; then
        echo "libnss3:${arch}"
    else
        echo "libnss3"
    fi
}
echo ""
if [ "$cacerts_updates" != yes ] || [ "$CACERT_UPDATES" = disabled ] || [ ! -e $JAR ]; then
    echo "updates of cacerts keystore disabled."
    exit 0
fi
if ! mountpoint -q /proc; then
    echo >&2 "the keytool command requires a mounted proc fs (/proc)."
    exit 1
fi
for jvm in java-7-openjdk-$arch java-7-openjdk \
           oracle-java7-jre-$arch oracle-java7-server-jre-$arch oracle-java7-jdk-$arch \
           java-8-openjdk-$arch java-8-openjdk \
           oracle-java8-jre-$arch oracle-java8-server-jre-$arch oracle-java8-jdk-$arch \
           java-9-openjdk-$arch java-9-openjdk \
           oracle-java9-jre-$arch oracle-java9-server-jre-$arch oracle-java9-jdk-$arch; do
if [ -x /usr/lib/jvm/$jvm/bin/java ]; then
    	break
fi
done
export JAVA_HOME=/usr/lib/jvm/$jvm
PATH=$JAVA_HOME/bin:$PATH
temp_jvm_cfg=
if [ ! -f /etc/${jvm%-$arch}/jvm-$arch.cfg ]; then
    # the jre is not yet configured, but jvm.cfg is needed to run it
    temp_jvm_cfg=/etc/${jvm%-$arch}/jvm-$arch.cfg
    mkdir -p /etc/${jvm%-$arch}
    printf -- "-server KNOWN\n" > $temp_jvm_cfg
fi
if dpkg-query --version >/dev/null; then
    nsspkg=$(dpkg-query -L "$(nsslib_name)" | sed -n 's,\(.*\)/libnss3\.so$,\1,p'|head -n 1)
    nsscfg=/etc/${jvm%-$arch}/security/nss.cfg
    nssjdk=$(test ! -f $nsscfg || sed -n '/nssLibraryDirectory/s/.*= *\(.*\)/\1/p' $nsscfg)
    if [ -n "$nsspkg" ] && [ -n "$nssjdk" ] && [ "$nsspkg" != "$nssjdk" ]; then
        ln -sf $nsspkg/libnss3.so $nssjdk/libnss3.so
    fi
    softokn3pkg=$(dpkg-query -L "$(nsslib_name)" | sed -n 's,\(.*\)/libsoftokn3\.so$,\1,p'|head -n 1)
    if [ -n "$softokn3pkg" ] && [ -n "$nssjdk" ] && [ "$softokn3pkg" != "$nssjdk" ]; then
        ln -sf $softokn3pkg/libsoftokn3.so $nssjdk/libsoftokn3.so
    fi
fi
do_cleanup()
{
    [ -z "$temp_jvm_cfg" ] || rm -f $temp_jvm_cfg
    if [ -n "$nsspkg" ] && [ -n "$nssjdk" ] && [ "$nsspkg" != "$nssjdk" ]
    then
        rm -f $nssjdk/libnss3.so
    fi
    if [ -n "$softokn3pkg" ] && [ -n "$nssjdk" ] \
       && [ "$softokn3pkg" != "$nssjdk" ]
    then
        rm -f $nssjdk/libsoftokn3.so
    fi
}
if java -Xmx64m -jar $JAR -storepass "$storepass"; then
    do_cleanup
else
    do_cleanup
    exit 1
fi
echo "done."
 |