Ceph

For a RHEL 8 machine, when multiple Python versions exist:

[zack@vossi04 ceph]$ ls /usr/bin/python3.[0-9]
/usr/bin/python3.6  /usr/bin/python3.8  /usr/bin/python3.9
[zack@vossi04 ceph]$ ls -l /usr/bin/python3
lrwxrwxrwx. 1 root root 25 Dec 11  2022 /usr/bin/python3 -> /etc/alternatives/python3
[zack@vossi04 ceph]$ ls -l /etc/alternatives/python3
lrwxrwxrwx 1 root root 18 Aug  9 19:18 /etc/alternatives/python3 -> /usr/bin/python3.9

the build system always picks up the newer python3.9 on a rebuild even when originally configured to use python 3.6. i.e.

./do_cmake.sh -DWITH_PYTHON3=3.6 ...

By rebuild I mean that the first build succeeds but if the HEAD commit sha1 changes, the rebuild will pick up the new python3 when regenerating cmake. This causes build failures like:

CMake Error at /usr/share/cmake/Modules/FindPackageHandleStandardArgs.cmake:230 (message):
  Could NOT find Python3: Found unsuitable version "3.9.13", but required is
  exact version "3.6" (found /usr/bin/python3, found components: Interpreter)