How to change the default GCC compiler in Ubuntu?

Question

I have installed gcc-3.3/g++-3.3 on ubuntu 11.04 which already has gcc/g++-4.4. So in my system both gcc-3.3 and 4.4 are available. I am able to call both compilers as I want. If I just call the command gcc then gcc-4.4 will get called. To call gcc-3.3, I have to use the command gcc-3.3.

How can I change the default compiler as gcc-3.3? When I execute the command gcc it should call the gcc-3.3 and not gcc-4.4.

In addition, how can I change the variable CXX in a make file to gcc-3.3? I wish to change one common global place in the system instead of changing all make files.

For CXX flag you can invoke `CXX=gcc-3.3` or `export CXX=gcc-3.3` and then `make` however when you changed it globally with `update-alternatives` it will already use gcc-3.3 and this is not necessary. — DipSwitch, Oct 20 '11 at 15:17
@RoboAlex: updated my answer again to take into account your CXX environment variable request. However, please note that it will only serve in case you modify the update-alternatives later. — jopasserat, Oct 20 '11 at 15:42
You only need to change your PATH. Most of the answers mention the alternatives system, but both the Debian and the LLVM maintainers agree that the *alternatives* system should be used for *alternatives*, NOT for *versioning*. Further explained in my answer. — hmijail, Nov 02 '17 at 09:13

score 133 · Accepted Answer · edited Jan 15 '15 at 23:46

As @Tommy suggested, you should use update-alternatives.
It assigns values to every software of a family, so that it defines the order in which the applications will be called.

It is used to maintain different versions of the same software on a system. In your case, you will be able to use several declinations of gcc, and one will be favoured.

To figure out the current priorities of gcc, type in the command pointed out by @tripleee's comment:

update-alternatives --query gcc

Now, note the priority attributed to gcc-4.4 because you'll need to give a higher one to gcc-3.3.
To set your alternatives, you should have something like this (assuming your gcc installation is located at /usr/bin/gcc-3.3, and gcc-4.4's priority is less than 50):

update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-3.3 50

--edit--

Finally, you can also use the interactive interface of update-alternatives to easily switch between versions. Type update-alternatives --config gcc to be asked to choose the gcc version you want to use among those installed.

--edit 2 --

Now, to fix the CXX environment variable systemwide, you need to put the line indicated by @DipSwitch's in your .bashrc file (this will apply the change only for your user, which is safer in my opinion):

echo 'export CXX=/usr/bin/gcc-3.3' >> ~/.bashrc

@thang also called `cc`: `root@host:/root# update-alternatives --get-selections | grep '/usr/bin/gcc' cc auto /usr/bin/gcc` — jopasserat, Aug 13 '16 at 15:26
When I run the 'update-alternatives --config gcc', nothing happens, even though I have the system's gcc and anaconda one — Kelthar, Apr 07 '19 at 11:13
how could you do this automatically though? this requires a manual step to check the output of `update-alternatives --query gcc`, which might not work eg in an automated provisioning script. Also, how can this be made platform agnostic? — ely, Jan 07 '20 at 15:55

score 77 · Answer 2 · answered Feb 01 '12 at 21:00

Here's a complete example of jHackTheRipper's answer for the TL;DR crowd. :-) In this case, I wanted to run g++-4.5 on an Ubuntu system that defaults to 4.6. As root:

apt-get install g++-4.5
update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-4.6 100
update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-4.5 50
update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-4.6 100
update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-4.5 50
update-alternatives --install /usr/bin/cpp cpp-bin /usr/bin/cpp-4.6 100
update-alternatives --install /usr/bin/cpp cpp-bin /usr/bin/cpp-4.5 50
update-alternatives --set g++ /usr/bin/g++-4.5
update-alternatives --set gcc /usr/bin/gcc-4.5
update-alternatives --set cpp-bin /usr/bin/cpp-4.5

Here, 4.6 is still the default (aka "auto mode"), but I explicitly switch to 4.5 temporarily (manual mode). To go back to 4.6:

update-alternatives --auto g++
update-alternatives --auto gcc
update-alternatives --auto cpp-bin

(Note the use of cpp-bin instead of just cpp. Ubuntu already has a cpp alternative with a master link of /lib/cpp. Renaming that link would remove the /lib/cpp link, which could break scripts.)

For the lazy person of the future trying to set the installed g++-5 compiler to be default: `sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-5 100` — geometrian, May 15 '15 at 10:58
Only 1 question remains: why won't APT do this when installing the `g++-6` package? — rustyx, Jan 26 '19 at 16:09
I switched the default compiler to g++-5 this way, but it still uses g++-7 standard libraries, and now i'm getting errors with undefined `__builtin` stuff. — Youda008, May 01 '19 at 08:17

Anton K · Answer 3 · 2014-09-06T05:36:23.900

28

This is the great description and step-by-step instruction how to create and manage master and slave (gcc and g++) alternatives.

Shortly it's:

sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-4.6 60 --slave /usr/bin/g++ g++ /usr/bin/g++-4.6
sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-4.7 40 --slave /usr/bin/g++ g++ /usr/bin/g++-4.7
sudo update-alternatives --config gcc

edited Sep 06 '14 at 05:36

answered Mar 12 '14 at 23:13

Anton K

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1

what's with the 40 and 60. I am trying to use gcc-6. – nyxee Jan 10 '17 at 09:29
1

@nyxee 40 and 60 denote the priority assigned to each entry, check the other answers for more completeness on the topic – jopasserat Apr 30 '17 at 10:46

szotsaki · Answer 4 · 2017-12-08T06:13:58.860

Between 4.8 and 6 with all --slaves:

update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-4.8 \
                    10 \
                    --slave   /usr/bin/cc cc /usr/bin/gcc-4.8 \
                    --slave   /usr/bin/c++ c++ /usr/bin/g++-4.8 \
                    --slave   /usr/bin/g++ g++ /usr/bin/g++-4.8 \
                    --slave   /usr/bin/gcov gcov /usr/bin/gcov-4.8 \
                    --slave   /usr/bin/gcov-dump gcov-dump /usr/bin/gcov-dump-4.8 \
                    --slave   /usr/bin/gcov-tool gcov-tool /usr/bin/gcov-tool-4.8 \
                    --slave   /usr/bin/gcc-ar gcc-ar /usr/bin/gcc-ar-4.8 \
                    --slave   /usr/bin/gcc-nm gcc-nm /usr/bin/gcc-nm-4.8 \
                    --slave   /usr/bin/gcc-ranlib gcc-ranlib /usr/bin/gcc-ranlib-4.8

and

update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-6 \
                    15 \
                    --slave   /usr/bin/cc cc /usr/bin/gcc-6 \
                    --slave   /usr/bin/c++ c++ /usr/bin/g++-6 \
                    --slave   /usr/bin/g++ g++ /usr/bin/g++-6 \
                    --slave   /usr/bin/gcov gcov /usr/bin/gcov-6 \
                    --slave   /usr/bin/gcov-dump gcov-dump /usr/bin/gcov-dump-6 \
                    --slave   /usr/bin/gcov-tool gcov-tool /usr/bin/gcov-tool-6 \
                    --slave   /usr/bin/gcc-ar gcc-ar /usr/bin/gcc-ar-6 \
                    --slave   /usr/bin/gcc-nm gcc-nm /usr/bin/gcc-nm-6 \
                    --slave   /usr/bin/gcc-ranlib gcc-ranlib /usr/bin/gcc-ranlib-6

Change between them with update-alternatives --config gcc.

works fine after removing `cc` and `c++` lines, which cause error: alternative cc can't be slave of gcc: it is a master alternative — palik, Nov 06 '18 at 14:37
This is the right approach. All GCC utilities should be configured. — Jingguo Yao, Apr 10 '22 at 08:33

dileks · Answer 5 · 2015-01-24T14:48:11.500

Now, there is gcc-4.9 available for Ubuntu/precise.

Create a group of compiler alternatives where the distro compiler has a higher priority:

root$ VER=4.6 ; PRIO=60
root$ update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-$VER $PRIO --slave /usr/bin/g++ g++ /usr/bin/g++-$VER
root$ update-alternatives --install /usr/bin/cpp cpp-bin /usr/bin/cpp-$VER $PRIO

root$ VER=4.9 ; PRIO=40
root$ update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-$VER $PRIO --slave /usr/bin/g++ g++ /usr/bin/g++-$VER
root$ update-alternatives --install /usr/bin/cpp cpp-bin /usr/bin/cpp-$VER $PRIO

NOTE: g++ version is changed automatically with a gcc version switch. cpp-bin has to be done separately as there exists a "cpp" master alternative.

List available compiler alternatives:

root$ update-alternatives --list gcc
root$ update-alternatives --list cpp-bin

To select manually version 4.9 of gcc, g++ and cpp, do:

root$ update-alternatives --config gcc
root$ update-alternatives --config cpp-bin

Check compiler versions:

root$ for i in gcc g++ cpp ; do $i --version ; done

Restore distro compiler settings (here: back to v4.6):

root$ update-alternatives --auto gcc
root$ update-alternatives --auto cpp-bin

score 4 · Answer 6 · answered Aug 18 '16 at 20:34

I found this problem while trying to install a new clang compiler. Turns out that both the Debian and the LLVM maintainers agree that the alternatives system should be used for alternatives, NOT for versioning.

The solution they propose is something like this:
PATH=/usr/lib/llvm-3.7/bin:$PATH
where /usr/lib/llvm-3.7/bin is a directory that got created by the llvm-3.7 package, and which contains all the tools with their non-suffixed names. With that, llvm-config (version 3.7) appears with its plain name in your PATH. No need to muck around with symlinks, nor to call the llvm-config-3.7 that got installed in /usr/bin.

Also, check for a package named llvm-defaults (or gcc-defaults), which might offer other way to do this (I didn't use it).

Excellent solution ! Me use it to for selecting amongst custom built "gcc" suites — Mad Calm, Aug 04 '20 at 20:15

score 1 · Answer 7 · answered Feb 28 '16 at 19:01

1

In case you want a quicker (but still very clean) way of achieving it for a personal purpose (for instance if you want to build a specific project having some strong requirements concerning the version of the compiler), just follow the following steps:

type echo $PATH and look for a personal directory having a very high priority (in my case, I have ~/.local/bin);
add the symbolic links in this directory:

For instance:

ln -s /usr/bin/gcc-WHATEVER ~/.local/bin/gcc
ln -s /usr/bin/g++-WHATEVER ~/.local/bin/g++

Of course, this will work for a single user (it isn't a system wide solution), but on the other hand I don't like to change too many things in my installation.

answered Feb 28 '16 at 19:01

Thomas Baruchel

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So you're creating your own ad-hoc, parallel-to-the-system's alternatives system. Why not use the real thing? – hmijail Aug 17 '16 at 17:32
@hmijail As I explained, I use this way when I want to build a very single project without messing up my whole installation. It works very well and I can easely remove it after. – Thomas Baruchel Aug 18 '16 at 18:16
1

Just changing your PATH would be faster, cleaner and would keep your gcc-related tools in sync with each other. – hmijail Aug 18 '16 at 20:38

score 0 · Answer 8 · answered Jan 10 '17 at 10:22

I used just the lines below and it worked. I just wanted to compile VirtualBox and VMWare WorkStation using kernel 4.8.10 on Ubuntu 14.04. Initially, most things were not working for example graphics and networking. I was lucky that VMWare workstation requested for gcc 6.2.0. I couldn't start my Genymotion Android emulators because virtualbox was down. Will post results later if necessary.

VER=4.6 ; PRIO=60
sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-$VER $PRIO --slave /usr/bin/g++ g++ /usr/bin/g++-$VER
VER=6 ; PRIO=50
sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-$VER $PRIO --slave /usr/bin/g++ g++ /usr/bin/g++-$VER
VER=4.8 ; PRIO=40
sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-$VER $PRIO --slave /usr/bin/g++ g++ /usr/bin/g++-$VER

How to change the default GCC compiler in Ubuntu?

8 Answers8

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