How to choose the default gcc and g++ version?

Question

So I have installed gcc-4.4 and gcc-4.3 (same for g++). Now as far as I remember there is a tool in Ubuntu which sets the symlinks for you if you just tell it which version you want. However it does not seem to work in the newest version, which I find disappointing.

root@nexus:~# update-alternatives --config gcc
update-alternatives: error: no alternatives for gcc.
root@nexus:~# update-alternatives --config cc
There is only one alternative in link group cc: /usr/bin/gcc
Nothing to configure.


root@nexus:~# dpkg -l | grep gcc | awk '{print $2}'
gcc
gcc-4.3
gcc-4.3-base
gcc-4.3-multilib
gcc-4.4
gcc-4.4-base
gcc-4.4-multilib
gcc-4.5-base
gcc-multilib
lib32gcc1
libgcc1

Any ideas?

Answer 1

First erase the current update-alternatives setup for gcc and g++:

sudo update-alternatives --remove-all gcc 
sudo update-alternatives --remove-all g++

Install Packages

It seems that both gcc-4.3 and gcc-4.4 are installed after install build-essential. However, we can explicitly install the following packages:

sudo apt-get install gcc-4.3 gcc-4.4 g++-4.3 g++-4.4

Install Alternatives

Symbolic links cc and c++ are installed by default. We will install symbol links for gcc and g++, then link cc and c++ to gcc and g++ respectively. (Note that the 10, 20 and 30 options are the priorities for each alternative, where a bigger number is a higher priority.)

sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-4.3 10
sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-4.4 20

sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-4.3 10
sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-4.4 20

sudo update-alternatives --install /usr/bin/cc cc /usr/bin/gcc 30
sudo update-alternatives --set cc /usr/bin/gcc

sudo update-alternatives --install /usr/bin/c++ c++ /usr/bin/g++ 30
sudo update-alternatives --set c++ /usr/bin/g++

Configure Alternatives

The last step is configuring the default commands for gcc, g++. It's easy to switch between 4.3 and 4.4 interactively:

sudo update-alternatives --config gcc
sudo update-alternatives --config g++

Or switch using script:

#!/bin/sh

if [ -z "$1" ]; then
    echo "usage: $0 version" 1>&2
    exit 1
fi

if [ ! -f "/usr/bin/gcc-$1" ] || [ ! -f "/usr/bin/g++-$1" ]; then
    echo "no such version gcc/g++ installed" 1>&2
    exit 1
fi

update-alternatives --set gcc "/usr/bin/gcc-$1"
update-alternatives --set g++ "/usr/bin/g++-$1"

Answer 2

execute in terminal :

gcc -v
g++ -v

Okay, so that part is fairly simple. The tricky part is that when you issue the command GCC it is actually a sybolic link to which ever version of GCC you are using. What this means is we can create a symbolic link from GCC to whichever version of GCC we want.

• You can see the symbolic link :

ls -la /usr/bin | grep gcc-4.4
ls -la /usr/bin | grep g++-4.4

• So what we need to do is remove the GCC symlink and the G++ symlink and then recreate them linked to GCC 4.3 and G++ 4.3:

rm /usr/bin/gcc
rm /usr/bin/g++

ln -s /usr/bin/gcc-4.3 /usr/bin/gcc
ln -s /usr/bin/g++-4.3 /usr/bin/g++

• Now if we check the symbolic links again we will see GCC & G++ are now linked to GCC 4.3 and G++ 4.3:

ls -la /usr/bin/ | grep gcc
ls -la /usr/bin/ | grep g++

• Finally we can check our GCC -v again and make sure we are using the correct version:

gcc -v
g++ -v

Answer 3

Is this really desirable? There are ABI changes between gcc versions. Compiling something with one version (eg the entire operating system) and then compiling something else with another version, can cause conflict.

For example, kernel modules should always be compiled with the same version of gcc used to compile the kernel. With that in mind, if you manually altered the symlink between /usr/bin/gcc and the version used in your version of Ubuntu, future DKMS-built modules might use the wrong gcc version.

If you just want to build things with a different version of gcc, that's easy enough, even with makescripts. For example, you can pass in the version of gcc in the CC environment variable:

CC="gcc-4.5" ./configure
CC="gcc-4.5" make

You might not need it on the make command (configure scripts usually pull it in) but it doesn't hurt.

Answer 4

I was looking to switch from gcc/g++ 9.x (was installed) to 10.x:

1. Installed the new desired version:

sudo apt install gcc-10
sudo apt install g++-10

2. Switch to the new version:

sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-10 10
sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-10 10

3. Test with:

gcc --version
g++ --version

The old version is still installed in case you need to switch back, just use the commands form 2. with your old version!

Answer 5

Edit:

This assumes that you have installed the version first, with e.g.:

sudo apt install gcc-4.9 g++-4.9

Original:

And here is a one-liner for those who are lazy, just change change the number at the end to the version you want. It will make the change for gcc and/or g++

ls -la /usr/bin/ | grep -oP "[\S]*(gcc|g\+\+)(-[a-z]+)*[\s]" | xargs bash -c 'for link in ${@:1}; do sudo ln -s -f "/usr/bin/${link}-${0}" "/usr/bin/${link}"; done' 4.9

In this example I switched to 4.9

There are no error checks and what not in this example, so you might want to check what will be run before you run it. Just add echo before sudo. For completeness I provide check line as well:

ls -la /usr/bin/ | grep -oP "[\S]*(gcc|g\+\+)(-[a-z]+)*[\s]" | xargs bash -c 'for link in ${@:1}; do echo sudo ln -s -f "/usr/bin/${link}-${0}" "/usr/bin/${link}"; done' 4.9

The output from the check should be something like:

sudo ln -s -f /usr/bin/g++-4.9 /usr/bin/g++
sudo ln -s -f /usr/bin/gcc-4.9 /usr/bin/gcc
sudo ln -s -f /usr/bin/gcc-ar-4.9 /usr/bin/gcc-ar
sudo ln -s -f /usr/bin/gcc-nm-4.9 /usr/bin/gcc-nm
sudo ln -s -f /usr/bin/gcc-ranlib-4.9 /usr/bin/gcc-ranlib
sudo ln -s -f /usr/bin/x86_64-linux-gnu-g++-4.9 /usr/bin/x86_64-linux-gnu-g++
sudo ln -s -f /usr/bin/x86_64-linux-gnu-gcc-4.9 /usr/bin/x86_64-linux-gnu-gcc
sudo ln -s -f /usr/bin/x86_64-linux-gnu-gcc-ar-4.9 /usr/bin/x86_64-linux-gnu-gcc-ar
sudo ln -s -f /usr/bin/x86_64-linux-gnu-gcc-nm-4.9 /usr/bin/x86_64-linux-gnu-gcc-nm
sudo ln -s -f /usr/bin/x86_64-linux-gnu-gcc-ranlib-4.9 /usr/bin/x86_64-linux-gnu-gcc-ranlib

You can check the version after with:

gcc --version

Semi-detailed explanation:

• ls -la /usr/bin/ lists all files in /usr/bin
• | pipe (send) the output to the next command
• grep -oP matches the search regex per line. o only shows the result not the entire matched line. P tells grep to use perl-regex. I will not go into regex here, read up on it if you want to.
• xargs simply put, it gathers the results that are piped to it and send all of them to the end. i.e. to the command following xargs
• bash well, it's bash. The c flag tells it to use the string as a command. In this example it loops over the arguments sent from xargs by skipping the first (0th) argument, in this case the loop skips 4.9. The 0th argument is used in the loop to change the link.
• ln -s -f The s flag makes a symbolic link, f forces unlinking first if needed.

Answer 6

I usually configure also related gcc tools (gcc-ar, ...) as slaves, so you can switch all of them at once:

sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-4.3 10 \
    --slave /usr/bin/gcc-ar gcc-ar /usr/bin/gcc-ar-4.3 \
    --slave /usr/bin/gcc-nm gcc-nm /usr/bin/gcc-nm-4.3 \
    --slave /usr/bin/gcc-ranlib gcc-ranlib /usr/bin/gcc-ranlib-4.3

sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-4.4 20 \
    --slave /usr/bin/gcc-ar gcc-ar /usr/bin/gcc-ar-4.4 \
    --slave /usr/bin/gcc-nm gcc-nm /usr/bin/gcc-nm-4.4 \
    --slave /usr/bin/gcc-ranlib gcc-ranlib /usr/bin/gcc-ranlib-4.4

sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-4.3 10
sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-4.4 20

Then to select the default one:

sudo update-alternatives --config gcc
sudo update-alternatives --config g++

Answer 7

How about a symbolic link in a temporary directory:

mkdir x && PATH=$PWD/x:$PATH && ln -s /usr/bin/g++-7 $PWD/x/g++

Answer 8

Using update-alternatives will introduce numerous small files and links into /etc/alternatives. Moreover, you have to do the selection for every compiler slave (i.e, gcc cpp g++ gcc-ar gcc-nm gcc-ranlib gcov gcov-dump gcov-tool lto-dump) in update-alternatives. For a cleaner and more straight-forward solution, just use bash for loop:

cd /usr/bin
for f in gcc cpp g++ gcc-ar gcc-nm gcc-ranlib gcov gcov-dump gcov-tool lto-dump; do
    ln -vsf $f-12 $f
done

Change 12 into any version that you intend to use by default.

By right, the g++ compiler package should contain package configuration for dpkg-reconfigure to select the default compiler version when multiple versions of compilers are present on the system, like when you install gdm, sddm, lightdm, it prompts to select the default display manager.

Answer 9

You can use the alternatives command I hope it helps!

sudo apt install build-essential

sudo apt install gcc-8 g++-8 gcc-9 g++-9 gcc-10 g++-10

sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-10 100 --slave /usr/bin/g++ g++ /usr/bin/g++-10 --slave /usr/bin/gcov gcov /usr/bin/gcov-10

sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-9 90 --slave /usr/bin/g++ g++ /usr/bin/g++-9 --slave /usr/bin/gcov gcov /usr/bin/gcov-9

sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-8 80 --slave /usr/bin/g++ g++ /usr/bin/g++-8 --slave /usr/bin/gcov gcov /usr/bin/gcov-8

sudo update-alternatives --config gcc

https://snipboard.io/zE4B9D.jpg

Answer 10

Complete set (I hope) of update-alternatives commands for gcc with slave entries for cpp, g++, gcc-ar, gcc-nm, gcc-ranlib, gcov, gcov-dump, gcov-tool, lto-dump & matching x86_64-linux-gnu- links! Implemented / tested on Debian bookworm (testing) Obviously, double-check before copy/pasting and hitting ⮐Enter

BACKGROUND

I'm not a programmer or coder or anything, but I do admin a number of Linux servers (CentOS and Debian) and run Debian testing at home.  Usually I just apt install something.  Rarely do I have to ./configure && make && make install so beyond that I don't have much knowledge.  Before this, I only knew of gcc and g++, but have discovered at least 15 other links associated with the GNU Compiler Collection on my system, each pointing to a corresponding binary or other link.

Today, I have GCC 12 installed and trying to build something, but it's some older code so GCC 12 is too new.  Time sure does fly, I remember when GCC 4 was common!  When I checked, my system has versions 8, 9, 10, and 11 also.  Yet when I updated GCC to point to the version 11 binaries, it didn't change anything.  I realized gcc-11 wasn't even a binary anymore.  It's a link now too, to x86_64-linux-gnu-gcc-11 which is the target binary.  In fact, all of the binaries now start with a x86_64-linux-gnu- and end with a -vers and have a corresponding generic link starting with x86_64-linux-gnu-.

I came up with this command then, to install the alternatives that can be switched with update-alternatives command.  Just replace the value of the vers variable in the beginning to correspond to the version you have installed, the priority will be based on the version, so version 12 has 120 priority, 11 has 110, and so on.  In the end, 20 links are updated for each version!

Multi-line:

vers=<vers>; update-alternatives \
  --install /usr/bin/gcc gcc /usr/bin/gcc-"${vers}" "${vers}"0 \
  --slave /usr/bin/x86_64-linux-gnu-gcc x86_64-linux-gnu-gcc /usr/bin/x86_64-linux-gnu-gcc-"${vers}" \
  --slave /usr/bin/g++ g++ /usr/bin/g++-"${vers}" \
  --slave /usr/bin/x86_64-linux-gnu-g++ x86_64-linux-gnu-g++ /usr/bin/x86_64-linux-gnu-g++-"${vers}" \
  --slave /usr/bin/cpp cpp /usr/bin/cpp-"${vers}" \
  --slave /usr/bin/x86_64-linux-gnu-cpp x86_64-linux-gnu-cpp /usr/bin/x86_64-linux-gnu-cpp-"${vers}" \
  --slave /usr/bin/gcc-ar gcc-ar /usr/bin/gcc-ar-"${vers}" \
  --slave /usr/bin/x86_64-linux-gnu-gcc-ar x86_64-linux-gnu-gcc-ar /usr/bin/x86_64-linux-gnu-gcc-ar-"${vers}" \
  --slave /usr/bin/gcc-nm gcc-nm /usr/bin/gcc-nm-"${vers}" \
  --slave /usr/bin/x86_64-linux-gnu-gcc-nm x86_64-linux-gnu-gcc-nm /usr/bin/x86_64-linux-gnu-gcc-nm-"${vers}" \
  --slave /usr/bin/gcc-ranlib gcc-ranlib /usr/bin/gcc-ranlib-"${vers}" \
  --slave /usr/bin/x86_64-linux-gnu-gcc-ranlib x86_64-linux-gnu-gcc-ranlib /usr/bin/x86_64-linux-gnu-gcc-ranlib-"${vers}" \
  --slave /usr/bin/gcov gcov /usr/bin/gcov-"${vers}" \
  --slave /usr/bin/x86_64-linux-gnu-gcov x86_64-linux-gnu-gcov /usr/bin/x86_64-linux-gnu-gcov-"${vers}" \
  --slave /usr/bin/gcov-dump gcov-dump /usr/bin/gcov-dump-"${vers}" \
  --slave /usr/bin/x86_64-linux-gnu-gcov-dump x86_64-linux-gnu-gcov-dump /usr/bin/x86_64-linux-gnu-gcov-dump-"${vers}" \
  --slave /usr/bin/gcov-tool gcov-tool /usr/bin/gcov-tool-"${vers}" \
  --slave /usr/bin/x86_64-linux-gnu-gcov-tool x86_64-linux-gnu-gcov-tool /usr/bin/x86_64-linux-gnu-gcov-tool-"${vers}" \
  --slave /usr/bin/lto-dump lto-dump /usr/bin/lto-dump-"${vers}" \
  --slave /usr/bin/x86_64-linux-gnu-lto-dump x86_64-linux-gnu-lto-dump /usr/bin/x86_64-linux-gnu-lto-dump-"${vers}"

Single line:
vers=<vers>; update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-"${vers}" "${vers}"0 --slave /usr/bin/x86_64-linux-gnu-gcc x86_64-linux-gnu-gcc /usr/bin/x86_64-linux-gnu-gcc-"${vers}" --slave /usr/bin/g++ g++ /usr/bin/g++-"${vers}" --slave /usr/bin/x86_64-linux-gnu-g++ x86_64-linux-gnu-g++ /usr/bin/x86_64-linux-gnu-g++-"${vers}" --slave /usr/bin/cpp cpp /usr/bin/cpp-"${vers}" --slave /usr/bin/x86_64-linux-gnu-cpp x86_64-linux-gnu-cpp /usr/bin/x86_64-linux-gnu-cpp-"${vers}" --slave /usr/bin/gcc-ar gcc-ar /usr/bin/gcc-ar-"${vers}" --slave /usr/bin/x86_64-linux-gnu-gcc-ar x86_64-linux-gnu-gcc-ar /usr/bin/x86_64-linux-gnu-gcc-ar-"${vers}" --slave /usr/bin/gcc-nm gcc-nm /usr/bin/gcc-nm-"${vers}" --slave /usr/bin/x86_64-linux-gnu-gcc-nm x86_64-linux-gnu-gcc-nm /usr/bin/x86_64-linux-gnu-gcc-nm-"${vers}" --slave /usr/bin/gcc-ranlib gcc-ranlib /usr/bin/gcc-ranlib-"${vers}" --slave /usr/bin/x86_64-linux-gnu-gcc-ranlib x86_64-linux-gnu-gcc-ranlib /usr/bin/x86_64-linux-gnu-gcc-ranlib-"${vers}" --slave /usr/bin/gcov gcov /usr/bin/gcov-"${vers}" --slave /usr/bin/x86_64-linux-gnu-gcov x86_64-linux-gnu-gcov /usr/bin/x86_64-linux-gnu-gcov-"${vers}" --slave /usr/bin/gcov-dump gcov-dump /usr/bin/gcov-dump-"${vers}" --slave /usr/bin/x86_64-linux-gnu-gcov-dump x86_64-linux-gnu-gcov-dump /usr/bin/x86_64-linux-gnu-gcov-dump-"${vers}" --slave /usr/bin/gcov-tool gcov-tool /usr/bin/gcov-tool-"${vers}" --slave /usr/bin/x86_64-linux-gnu-gcov-tool x86_64-linux-gnu-gcov-tool /usr/bin/x86_64-linux-gnu-gcov-tool-"${vers}" --slave /usr/bin/lto-dump lto-dump /usr/bin/lto-dump-"${vers}" --slave /usr/bin/x86_64-linux-gnu-lto-dump x86_64-linux-gnu-lto-dump /usr/bin/x86_64-linux-gnu-lto-dump-"${vers}"