It looks like the openjdk-7 for ubuntu xenial is no more available in the selected PPA.
Browsing http://ppa.launchpad.net/openjdk-r/ppa/ubuntu/dists/xenial/main/binary-amd64/ show that the Packages.gz have been updated on 2021-04-21 and there is (no more?) references to a jdk older than openjdk-9
There are .deb in http://ppa.launchpad.net/openjdk-r/ppa/ubuntu/pool/main/o/openjdk-7/ but probably only for Lucid Lynx.
--- Last lines of docker build -t docker-idrac6 . ---
gpg: keyring `/tmp/tmpx3vyk1p4/secring.gpg' created
gpg: keyring `/tmp/tmpx3vyk1p4/pubring.gpg' created
gpg: requesting key 86F44E2A from hkp server keyserver.ubuntu.com
gpg: /tmp/tmpx3vyk1p4/trustdb.gpg: trustdb created
gpg: key 86F44E2A: public key "Launchpad OpenJDK builds (all archs)" imported
gpg: Total number processed: 1
gpg: imported: 1 (RSA: 1)
OK
Hit:1 http://archive.ubuntu.com/ubuntu xenial InRelease
Hit:2 http://deb.nodesource.com/node_12.x xenial InRelease
Hit:3 http://archive.ubuntu.com/ubuntu xenial-updates InRelease
Get:4 http://ppa.launchpad.net/openjdk-r/ppa/ubuntu xenial InRelease [23.8 kB]
Hit:5 http://archive.ubuntu.com/ubuntu xenial-backports InRelease
Hit:6 http://security.ubuntu.com/ubuntu xenial-security InRelease
Get:7 http://ppa.launchpad.net/openjdk-r/ppa/ubuntu xenial/main amd64 Packages [18.9 kB]
Fetched 42.8 kB in 0s (75.6 kB/s)
Reading package lists...
Reading package lists...
Building dependency tree...
Reading state information...
Package openjdk-7-jdk is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Package 'openjdk-7-jdk' has no installation candidate
The command '/bin/sh -c apt-get update && apt-get install -y wget software-properties-common && add-apt-repository ppa:openjdk-r/ppa && apt-get update && apt-get install -y openjdk-7-jdk gcc && gcc -o /keycode-hack.so /keycode-hack.c -shared -s -ldl -fPIC && apt-get remove -y gcc software-properties-common && apt-get autoremove -y && rm -rf /var/lib/apt/lists/* && rm /keycode-hack.c' returned a non-zero code: 100
It looks like the openjdk-7 for ubuntu xenial is no more available in the selected PPA.
Browsing http://ppa.launchpad.net/openjdk-r/ppa/ubuntu/dists/xenial/main/binary-amd64/ show that the Packages.gz have been updated on 2021-04-21 and there is (no more?) references to a jdk older than openjdk-9
There are .deb in http://ppa.launchpad.net/openjdk-r/ppa/ubuntu/pool/main/o/openjdk-7/ but probably only for Lucid Lynx.
--- Last lines of
docker build -t docker-idrac6 .---