### problem installing sage on ubuntu18.04

As written on the download page, I wanted to get the linux binaries. I can't find them.
I've obtained the source tarball for ubuntu18.4 (64bits).

I've unarchived the directory `Sagemath`

and cd'ed there. I type `make`

as explained.
This is the message I obtain:

RecursionError: maximum recursion
depth exceeded during compilation
Makefile:31: recipe for target
'base-toolchain' failed make: ***
[base-toolchain] Error 1

I've tried to install sage via apt with `sudo apt install sagemath-common`

all goes well, no error message. Then try to run sage and obtain the following message:

│ SageMath version 8.1, Release Date:
2017-12-07 │ │
Type "notebook()" for the
browser-based notebook interface.

│ │ Type "help()" for help.

│ Traceback (most recent call last):

File "/usr/share/sagemath/bin/sage-ipython", line 7, in <module>
from sage.repl.interpreter import SageTerminalApp
ImportError: No module named 'sage'

I had a working sage (7.?) on the same machine under ubuntu16.04 which stopped working under ubuntu18.04.
I've deleted the Sage and also the .sage directories before trying all the above.

I am at my wit's end and would greatly appreciate any help.