Creating and using chroots and containers

chroots and containers can be set up and used for many purposes, including:

• running glibc software on musl (and vice versa)
• running software in a more controlled or sandboxed environment
• creating a rootfs for bootstrapping a system

Chroot Creation

xvoidstrap

xvoidstrap(1) (from xtools) can be used to create the chroot:

# mkdir <chroot_dir>
# XBPS_ARCH=<chroot_arch> xvoidstrap <chroot_dir> base-container <other_pkgs>

<other_pkgs> is only needed if you want to pre-install other packages in the chroot.

Manual Creation

Alternatively, this process can be done manually.

Create a directory that will contain the chroot, then install a base system in it via the base-container package:

# mkdir -p "<chroot_dir>/var/db/xbps/keys"
# cp -a /var/db/xbps/keys/* "<chroot_dir>/var/db/xbps/keys"
# XBPS_ARCH=<chroot_arch> xbps-install -S -r <chroot_dir> -R <repository> base-container <other_pkgs>

The <repository> may vary depending on architecture.

<other_pkgs> is only needed if you want to pre-install other packages in the chroot.

Chroot Usage

xchroot

xchroot(1) (from xtools) can be used to automatically set up and enter the chroot.

Manual Method

Alternatively, this process can be done manually.

If network access is required, copy /etc/resolv.conf into the chroot; /etc/hosts may need to be copied as well.

Several directories then need to be mounted as follows:

# mount -t proc none <chroot_dir>/proc
# mount -t sysfs none <chroot_dir>/sys
# mount --rbind /dev <chroot_dir>/dev
# mount --rbind /run <chroot_dir>/run

Use chroot(1) to change to the new root, then run programs and do tasks as usual. Once finished with the chroot, unmount the chroot using umount(8). If any destructive actions are taken on the chroot directory without unmounting first, you may need to reboot to repopulate the affected directories.

Alternatives

Bubblewrap

bwrap(1) (from the bubblewrap package) has additional features like the ability for sandboxing and does not require root access.

bwrap is very flexible and can be used in many ways, for example:

$ bwrap --bind <chroot_dir> / \
	--dev /dev \
	--proc /proc \
	--bind /sys /sys \
	--bind /run /run \
	--ro-bind /etc/resolv.conf /etc/resolv.conf \
	--ro-bind /etc/passwd /etc/passwd \
	--ro-bind /etc/group /etc/group \
	<command>

In this example, you will not be able to add or edit users or groups. When running graphical applications with Xorg, you may need to also bind-mount ~/.Xauthority or other files or directories.

The bwrap(1) manpage and the Arch Wiki article contain more examples of bwrap usage.

Flatpak

Flatpak is a convenient option for running many applications, including graphical or proprietary ones, on both glibc and musl systems.

Application Containers

If a more integrated and polished solution is desired, Void also provides OCI containers that work with tools like docker and podman. These containers do not require the creation of a chroot directory before usage.