Hi,
I just installed cadabra2by compiling from source on a machine running Linux Mint 18. I tested the command line version of cadabra, and it seems to work well (albeit with simple addition/multiplication of numerical and algebraic expresions; not with tensor quantities). The GUI version fails. After firing the gui with cadabra2-gtk I do get the GUI but evaluating a cell always fails, no matter what expression is in the cell. The message "cadabra-client: connection failed" prints on the terminal from which I fired Cadabra. I traced it to a function/method in ComputeThread.cc under the client_server subdirectory in the source code.
Any suggestions to get around this problem? Any help will be appreciated.

What happens if you try to start cadabra-server from a terminal window?

Selecting menus works in my case (e.g. "Edit -> Insert cell above" immediately responds by inserting the cell). But evaluating a cell for something as simple as "8 - 2; ", the GUI hangs indefinitely. On the bottom right corner it has "idle", which I presume indicates the state of the kernel (whether or not it is performing some calculation).

Does the GUI say 'connected' at the bottom?

No, it doesn't. It only says 'idle'.

route -n


in the terminal and send me the output?

Here is the output:

\$ route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         146.231.61.129  0.0.0.0         UG    100    0        0 enp0s25
146.231.61.128  0.0.0.0         255.255.255.128 U     100    0        0 enp0s25
146.231.129.20  146.231.61.129  255.255.255.255 UGH   100    0        0 enp0s25
169.254.0.0     0.0.0.0         255.255.0.0     U     1000   0        0 enp0s25