How can I downgrade GCC to version 6 on 20.04?

I need GCC6 to compile CUDA9 files.


apt install gcc-6 is giving me this error:

Package gcc-6 is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'gcc-6' has no installation candidate
  • I'm looking for GCC 6 not g++6, do you happen to know the universe repo url for this package? Thanks
    – nnpractice
    May 7, 2020 at 12:00
  • @KnudLarsen Universe and Multiverse repos are already there. How would I install GCC6 in 20.04?
    – nnpractice
    May 7, 2020 at 12:31
  • I added this line: deb http://archive.ubuntu.com/ubuntu $(lsb_release -sc) bionic main universe to /etc/apt/sources.list. And typed apt install g++-6 and got the error: Package 'g++-6' has no installation candidate.
    – nnpractice
    May 7, 2020 at 14:44
  • I also modified the line and removed this part $(lsb_release -sc) so that after the word ubuntu there is a space and bionic. Saved it and tried to install but got the same error.
    – nnpractice
    May 7, 2020 at 14:54
  • Ubuntu 20.04 : I added deb http://dk.archive.ubuntu.com/ubuntu/ bionic main universe and did sudo apt update && sudo apt install g++-6 : All OK. gcc-6, g++-6 was installed. May 7, 2020 at 16:26

1 Answer 1


Ubuntu 20.04, gcc-6

Please do not remove / change the system gcc : You can have as many gcc versions as you want, installed at the same time. Add (temporarily) a line to /etc/apt/sources.list :

apt [url] bionic main universe, and do

sudo apt update
sudo apt install g++-6

My test : {gcc-6, g++-6} was installed OK.

Using extra compilers, examples : export CC=gcc-6 CXX=g++-6 && ./configure and make CC=gcc-6 CXX=g++-6

Other (non PIE) extra compilers for Ubuntu https://drive.google.com/drive/folders/1xVEATaYAwqvseBzYxKDzJoZ4-Hc_XOJm?usp=sharing

  • in your answer you didn't mention the link you wrote to add to the sources file.
    – nnpractice
    May 7, 2020 at 17:49
  • I meant this URL: deb http://dk.archive.ubuntu.com/ubuntu/ bionic main universe
    – nnpractice
    May 7, 2020 at 18:45
  • The local mirror is my example. You can use any other valid mirror / URL. May 7, 2020 at 22:30
  • But you should mentioned because when I used deb http://archive.ubuntu.com/ubuntu I got errors. I was able later when you mentioned that because gcc-6 and g++-6 was available on your local server. Those are not available on global mirrors for bionic.
    – nnpractice
    May 8, 2020 at 8:43
  • gcc-6, g++-6 etc. seems to be present at archive.ubuntu.com/ubuntu → universe/g/gcc-6 → archive.ubuntu.com/ubuntu/pool/universe/g/gcc-6 .... so quite puzzling why you cannot fetch it. May 8, 2020 at 8:55

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