# Issue with Linux (Ubuntu 16.04) install of Itensor V3

I previously had no issue installing V2 on my device. However, now when I run 'make', I get the error: "g++: error: unrecognized command line option '-fconcepts' ".

No doubt this is an issue with the compiler flag in the line
" CCCOM=g++ -m64 -std=c++17 -fconcepts -fPIC "
of the options.mk file. As a test, I tried removing the flag, but the compile again failed.

My best guess is that this has to do with the compiler and c++17, but I've had little luck with Google.

Any help would be appreciated!

commented by (7.3k points)
What version of g++ are you using? You can get the version by typing g++ --version at the command line. It may just be an issue of having an older compiler.
commented by (370 points)
Thank you for responding Matt. You are correct. It seems as though, even though I had the most recent compiler installed, g++ was defaulting to an older version when called. I found that modifying the above line of code to:
"CCCOM=g++-7 -m64 -std=c++17 -fconcepts -fPIC"
resolved the issue. Now everything compiled.