With buildah I am trying to build a container
image that should only contain the program cowsay and its dependencies.
I am doing this on a Fedora 29 computer where I don't have root permissions. Instead of using a Dockerfile and the command buildah build-using-dockerfile (aka buildah bud) I would like to
/usr/bin/dnf on my host system to install packages directly into the file system under the mount point. The command buildah from scratch creates an empty container but when I try to mount the file system I get an error
[testuser@linux ~]$ container=$(buildah from scratch)
[testuser@linux ~]$ mnt=$(buildah mount $container)
cannot mount using driver overlay in rootless mode
ERRO[0000] exit status 1
[testuser@linux ~]$
Some more information
[testuser@linux ~]$ cat /etc/redhat-release
Fedora release 29 (Twenty Nine)
[testuser@linux ~]$ buildah --version
buildah version 1.6 (image-spec 1.0.0, runtime-spec 1.0.0)
[testuser@linux ~]$
What goes wrong? How can I build the container image from scratch as a non-root user?
buildah unshare is needed to create an unshare environment. That was missing which led to the error message
cannot mount using driver overlay in rootless mode .
To build the container image create the file build.sh with this content
container=$(buildah from scratch)
mnt=$(buildah mount $container)
LC_ALL=C dnf install --installroot $mnt --release 29 --setopt=install_weak_deps=False -q -y cowsay
LC_ALL=C dnf --installroot $mnt clean all
buildah umount $container
buildah commit $container cowsay-container1
Then run the script build.sh inside an unshare environment
[testuser@linux ~]$ buildah unshare bash build.sh
List all images to see the newly built container image
[testuser@linux ~]$ buildah images
IMAGE NAME IMAGE TAG IMAGE ID CREATED AT SIZE
localhost/cowsay-container1 latest 9d9b88a8d5f1 Feb 18, 2019 17:26 307 MB
[testuser@linux ~]$
To try out the the newly built container image run
[testuser@linux ~]$ podman run localhost/cowsay-container1 cowsay hello
_______
< hello >
-------
\ ^__^
\ (oo)\_______
(__)\ )\/\
||----w |
|| ||
[testuser@linux ~]$
The build.sh script could be improved by adding some buildah config commands to provide some metadata information (e.g. buildah config --created-by and buildah config --cmd).
Instead of building the container image with the script build.sh, it is also possible to step into the unshare environment and run build commands manually.
[testuser@linux ~]$ cat /etc/redhat-release
Fedora release 29 (Twenty Nine)
[testuser@linux ~]$ buildah unshare
[root@linux ~]# container=$(buildah from scratch)
[root@linux ~]# mnt=$(buildah mount $container)
[root@linux ~]# LC_ALL=C dnf install --installroot $mnt --release 29 --setopt=install_weak_deps=False -q -y cowsay
warning: /home/testuser/.local/share/containers/storage/overlay/cc67b957fb78eebe6a861a8b69ef4728d0660a636645813224b6ba94fbc80ce0/merged/var/cache/dnf/updates-0b4cc238d1aa4ffe/packages/bash-4.4.23-6.fc29.x86_64.rpm: Header V3 RSA/SHA256 Signature, key ID 429476b4: NOKEY
Importing GPG key 0x429476B4:
Userid : "Fedora 29 (29) <fedora-29@fedoraproject.org>"
Fingerprint: 5A03 B4DD 8254 ECA0 2FDA 1637 A20A A56B 4294 76B4
From : /etc/pki/rpm-gpg/RPM-GPG-KEY-fedora-29-x86_64
[root@linux ~]# LC_ALL=C dnf --installroot $mnt clean all
33 files removed
[root@linux ~]# buildah umount $container
020ee8e3fb29274a306c441770d2458c732e84076cc0487ce6ea06ac957640d4
[root@linux ~]# buildah commit $container cowsay-container2
Getting image source signatures
Copying blob b3fbecd80150: 292.45 MiB / 292.45 MiB [========================] 2s
Copying config 8aa2ad2933ce: 263 B / 263 B [================================] 0s
Writing manifest to image destination
Storing signatures
8aa2ad2933ce33c8ed8b7551c4a3261177ebd811c9b813b40d5ea77536ac6ef5
[root@linux ~]# exit
exit
[testuser@linux ~]$ buildah images
IMAGE NAME IMAGE TAG IMAGE ID CREATED AT SIZE
localhost/cowsay-container1 latest 9d9b88a8d5f1 Feb 18, 2019 17:26 307 MB
localhost/cowsay-container2 latest 8aa2ad2933ce Feb 18, 2019 17:47 307 MB
[testuser@linux ~]$ podman run localhost/cowsay-container2 cowsay hello
_______
< hello >
-------
\ ^__^
\ (oo)\_______
(__)\ )\/\
||----w |
|| ||
[testuser@linux ~]$