Ceph

While building ceph:

[ 86%] Building CXX object src/test/mon/CMakeFiles/ceph_test_mon_memory_target.dir/test_mon_memory_target.cc.o
/root/ceph/src/test/mon/test_mon_memory_target.cc: In function ‘int main(int, char**)’:
/root/ceph/src/test/mon/test_mon_memory_target.cc:66:16: error: ‘sqrt’ was not declared in this scope
66 | auto stdev = sqrt(sump / results.size()); | ^~~~
make²: * [src/test/mon/CMakeFiles/ceph_test_mon_memory_target.dir/build.make:63: src/test/mon/CMakeFiles/ceph_test_mon_memory_target.dir/test_mon_memory_target.cc.o] Error 1
make¹: [CMakeFiles/Makefile2:15575: src/test/mon/CMakeFiles/ceph_test_mon_memory_target.dir/all] Error 2
make: ** [Makefile:141: all] Error 2

Adding the header cmath to the test file will fix it.