Red Hat Enterprise Linux, in the grand tradition of enterprise software vendors, packages and supports old mold long after it should be dead and buried. They don’t do this out of laziness, but because that is what their customers want. A lot of businesses view software the same way they see furniture: you buy a desk once and keep it forever, and software is just like a desk.
CentOS, as a RHEL clone, suffers from this as well. Red Hat supports deprecated software that is no longer supported by upstream — presumably patching security holes and keeping it working. But that is not good enough when you are running a software stack that requires newer versions. I have bumped into this numerous times running web servers on RHEL and CentOS. LAMP stacks are not forgiving, and every piece of the stack must be compatible with all of the others. For example, last year I had ongoing drama with RHEL/CentOS because version 6 shipped with PHP 5.3, and version 7 had PHP 5.4. PHP 5.3 was end-of-life in August, 2014 and unsupported by upstream. PHP 5.4 went EOL in Sept. 2015, and 5.5 in July 2016. MySQL, Python, and many other ancient packages that should be on display in museums as mummies also ship in these releases.
So, what’s a despairing admin to do? If you run both RHEL and CentOS turn first to the Software Collections, as this is only Red Hat-supported source of updated packages. There is a Software Collections repository for CentOS, and installing and managing it is similar to any third-party repository, with a couple of unique twists. (If you’re running RHEL, the procedure is different, as it is for all software management; you must do it the RHEL way.) Software Collections also supports Fedora and Scientific Linux.
Installing Software Collections
Install Software Collections on CentOS 6 and 7 with this command:
$ sudo yum install centos-release-scl
Then use Yum to search for and install packages in the usual way:
$ yum search php7 [...] rh-php70.x86_64 : Package that installs PHP 7.0 [...] $ sudo yum install rh-php70
This may also pull in centos-release-scl-rh as a dependency.
There is one more step, and that is enabling your new packages:
$ scl enable rh-php70 bash $ php -v PHP 7.0.10
This runs a script that loads the new package and changes your environment, and you should see a change in your prompt. You must also install the appropriate connectors for the new package if necessary, for example for Python, PHP, and MySQL, and update configuration files (e.g., Apache) to use the new version.
The SCL package will not be active after reboot. SCL is designed to run your old and new versions side-by-side and not overwrite your existing configurations. You can start your new packages automatically by sourcing their enable scripts in .bashrc. SCL installs everything into opt, so add this line to .bashrc for our PHP 7 example:
source /opt/rh/rh-php70/enable
It will automatically load and be available at startup, and you can go about your business cloaked in the warm glow of fresh up-to-date software.
Listing Available Packages
So, what exactly do you get in Software Collections on CentOS? There are some extra community-maintained packages in centos-release-scl. You can see package lists in the CentOS Wiki, or use Yum. First, let’s see all our installed repos:
$ yum repolist [...] repo id repo name base/7/x86_64 CentOS-7 - Base centos-sclo-rh/x86_64 CentOS-7 - SCLo rh centos-sclo-sclo/x86_64 CentOS-7 - SCLo sclo extras/7/x86_64 CentOS-7 - Extras updates/7/x86_64 CentOS-7 - Updates
Yum does not have a simple command to list packages in a single repo, so you have to do this:
$ yum --disablerepo "*" --enablerepo centos-sclo-rh list available | less
This use of the --disablerepo and --enablerepo options is not well documented. You’re not really disabling or enabling anything, but only limiting your search query to a single repo. It spits out a giant list of packages, and that is why we pipe it through less.
EPEL
The excellent Fedora peoples maintain the EPEL, Extra Packages for Enterprise Linux repository for Fedora and all RHEL-compatible distributions. This contains updated package versions and software that is not included in the stock distributions. Install software from EPEL in the usual way, without having to bother with enable scripts. Specify that you want packages from EPEL using the --disablerepo and --enablerepo options:
$ sudo yum --disablerepo "*" --enablerepo epel install [package]
Remi Collet
Remi Collet maintains a large collection of updated and extra packages at Remi’s RPM repository. Install EPEL first as Remi’s repo depends on it.
The CentOS wiki has a list of additional third-party repositories to use, and some to avoid.
Learn more about Linux through the free “Introduction to Linux” course from The Linux Foundation and edX.
