To install the full tools-set including gfortran on centos 7:

yum install centos-release-scl
yum install devtoolset-8
scl enable devtoolset-8 -- bash

enable the tools:

source /opt/rh/devtoolset-8/enable 

you may wish to put the command above in .bash_profile

ref: https://unix.stackexchange.com/questions/477360/centos-7-gcc-8-installation

Now devtools-8 is available and it's possible to use it by following commands:

yum install centos-release-scl
yum install devtoolset-8-gcc devtoolset-8-gcc-c++
scl enable devtoolset-8 -- bash

It's explained in a little more detail in this answer on StackOverflow: How to install GCC/G++ 8 on CentOS. And of course, if you need GFortran, you can install it in the same way - the package is devtoolset-8-gcc-gfortran.

I am using CentOS 7.9 and I encountered the same problem after following instructions here to install and run gcc 11. I tried launching different versions of gcc and found only devtoolset-9 works, which corresponds to the file devtoolset-9 in /etc/scl/conf/ folder. So I copied devtoolset-9 to devtoolset-11 in the same folder, and gcc 11 gets working.

Figured it out. cmake was using an old version of gcc/g++, not the one that my command line was picking up when I ran gcc or g++ myself. So, I had to export CC and CXX to the appropriate paths before running cmake.

export CC=/opt/rh/devtoolset-7/root/usr/bin/gcc
export CXX=/opt/rh/devtoolset-7/root/usr/bin/g++
cmake3 -G "Unix Makefiles" -DCMAKE_BUILD_TYPE=Release ..

Previously, I was only running the last line above.

Since the package is either not available, or using a different name, the first step is to find which is the case. Use

yum list available |grep gcc
yum list available |grep devtoolset

to find whether you have misspelled the package name, or if gcc is available under a different name. Check using yum info for the package. Its description should show the relevant version information.

According to Red Hat's article What gcc versions are available in Red Hat Enterprise Linux?, gcc 4.8 is available for Red Hat Enterprise 7. If you need gcc 4.8 for RHEL 6, you may have to compile it yourself.

Further reading:

• Installing GCC 4.8.2 on Red Hat Enterprise linux 6.5
• How to Install gcc 4.7.x/4.8.x on CentOS
• install latest gcc on rhel 6 x86_64