Installing CentOS in a chroot under Debian

This guide assumes you have a working Debian 10 (Buster) system and describes the steps needed to install a minimal CentOS 7 version into a chroot in it. Such installation can be useful if you need to build software for CentOS and/or Red Hat Enterprise Linux users.

Initial booststap using rinse

Debian packages rinse script in the package with the same, which can be used to create minimal installations of many RPM-based systems. Start by installing and then just run it, as root:

# apt install rinse
# rinse --arch amd64 --distribution centos-7 \
  --directory /srv/chroot/centos-7

It can be useful to additionally specify the --mirror option to select a particular mirror to use. This option also allows to explicitly select an exact CentOS version instead of installing the latest one by default, e.g. appending --mirror http://centos.mirrors.proxad.net/7.6.1810/os/x86_64/Packages to the command line above would download CentOS 7.6 packages from a particular mirror in France (mirrors close to your location can be found at this page).

Creating minimal /dev entries

CentOS 7 doesn't seem to provide the MAKEDEV script any longer, so the minimal set of required devices needs to be created by hand, i.e. executing the following commands inside the chroot:

# mknod /dev/null c 1 3
# chmod 666 /dev/null
# mknod /dev/ptmx c 5 2
# chmod 666 /dev/ptmx
# mkdir /dev/pts

Sharing users between the host system and chroot

Generally speaking, it's convenient to be able to reuse the same user in both the main, Debian, system and in chroot. For a single user it's enough to just create the same user entry in the chroot directory:

# chroot /srv/chroot/centos-7.6 adduser --no-create-home \
  --uid $USER_ID $USER_NAME

The --no-create-home option is used because we plan on reusing the home directories from the main system in the chroot, see the next section.

Mounting chroot filesystems

While not, strictly speaking, required, it is recommended to at least mount the /proc pseudo filesystem. Many tools also require the ability to create the pseudo-terminal devices, for which devpts must be mounted as well. And if you also decide to share the home directories between the main system and chroot, you need to use a bind-mount for it.

Taken together, this means that the following commands need to be executed:

# mount -t proc proc /srv/chroot/centos-7.6/proc
# mount -t devpts devpts /srv/chroot/centos-7.6/dev/pts
# mount -o bind /home /srv/chroot/centos-7.6/home

It also recommended to add the lines

proc /srv/chroot/centos-7.6/proc proc defaults 0 0
devpts /srv/chroot/centos-7.6/devpts devpts gid=5,mode=620 0 0
/home /srv/chroot/centos-7.6/home none bind 0 0

to /etc/fstab of the main system in order to make these mounts persistent.

Useful packages not included in the minimal installation

Installing ncurses-term is required in order to have non-dumb terminal functionality: this package provides the necessary terminfo entries.

The development tools included in CentOS 7 are quite ancient by now and it's recommended to install the latest version of RedHat development toolset to get the newer versions. For this the following commands need to be used:

# yum -y install centos-release-scl
# yum-config-manager --enable rhel-server-rhscl-7-rpms
# yum install devtoolset-8 rh-git218

Of course, remember to use

$ scl enable devtoolset-8 rh-git218 $SHELL

to actually enable using the programs included in these packages.