The one I always ends with is:
Linux gae-default-1-c9cf 3.16.0-4-amd64 #1 SMP Debian 3.16.36-1+deb8u2 (2016-10-19) x86_64
ldd (Debian EGLIBC 2.13-38+deb7u11) 2.13
apt-get install libc6
Reading package lists... Done
Building dependency tree
Reading state information... Done
libc6 is already the newest version.
0 upgraded, 0 newly installed, 0 to remove and 5 not upgraded.
-bash: /etc/apt/sources.list: Permission denied
Yes, you can build a custom dockerfile either by referring one which fits your requirements or specifying it from scratch: Building Custom Runtimes