Linux containers, or LXC, is a lightweigt yet powerful container solution. It can run applications or distros but (unlike virtual machines) share the same kernel and hardware resources and (unlike Docker) persistently.
This is not a cutting-edge technology and is fully supported in Fedora. However, the official Wiki page describes only a hard way to create and run LXC containers. It is time for a missing (but not the only) guide.
Install LXC and Supporting Tools
LXC and, additionally, related template files needs to be installed to enable easy usage of LXC.
$ sudo dnf install lxc lxcfs lxc-templatesNow we can get familiar with all LXC executables or commands:
$ ls /usr/bin/lxc*
lxc-attach lxc-config lxc-device lxc-ls lxc-top lxc-wait
lxc-autostart lxc-console lxc-execute lxc-monitor lxc-unfreeze
lxc-cgroup lxc-copy lxc-freeze lxc-snapshot lxc-unshare
lxc-checkconfig lxc-create lxcfs lxc-start lxc-update-config
lxc-checkpoint lxc-destroy lxc-info lxc-stop lxc-usernsexec The templates package will add useful scripts in the LXC templates directory:
$ ls /usr/share/lxc/templates
lxc-busybox lxc-download lxc-local lxc-ociCurrently (until Mar 2021), LXD is not packaged in Fedora.
Configure Linux Containers
Define UID Mappings
LXC is shipped with some default vaules. Unfortunately some of them is not correct and block the creating process of unprivileged containers:
lxc-create: example_container: parse.c: lxc_file_for_each_line_mmap: 80 No such file or directory - Failed to open file "/home/asaba/.config/lxc/default.conf"
lxc-create: example_container: conf.c: userns_exec_mapped_root: 4489 No uid mapping for container root
....
lxc-create: example_container: lxccontainer.c: do_lxcapi_create: 1871 Failed to create (none) storage for example_container
lxc-create: example_container: tools/lxc_create.c: main: 319 Failed to create container example_containerThis could be fixed by creating ~/.config/lxc/default.conf with the recommended content:
lxc.include = /etc/lxc/default.conf
lxc.idmap = u 0 100000 65536
lxc.idmap = g 0 100000 65536Configure LXC Network
We can re-use virbr0 created by libvirtd to simplify the configuration process:
$ BRIF=virbr0
$ echo "`whoami` veth ${BRIF} 10" > /etc/lxc/lxc-usernetCreate Containers
LXC container images could be either pulled (downloaded and imported) or built. Either method requires some scripting to generate images. Lucky we can use templates, and we also have a tool script from lxc-templates package to pull images from linuxcontainers.org or other download server.
List Available Images
First we can have a look at what images are available:
$ /usr/share/lxc/templates/lxc-download --list
Setting up the GPG keyring
Downloading the image index
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DIST RELEASE ARCH VARIANT BUILD
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....Create Privileged Containers
Containers could be created as privileged where the container uid 0 is mapped to the host's uid 0.
$ CONTAINER_NAME=guilin
$ sudo lxc-create -n ${CONTAINER_NAME} -t /usr/share/lxc/templates/lxc-download -- --dist debian --release stretch --arch amd64Setting up the GPG keyring
Downloading the image index
Downloading the rootfs
Downloading the metadata
The image cache is now ready
Unpacking the rootfs
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You just created a Debian stretch amd64 (20210309_05:24) container.
To enable SSH, run: apt install openssh-server
No default root or user password are set by LXC.Create Unprivileged Containers
Containers could also be unprivileged.
$ CONTAINER_NAME=guilin
$ lxc-create -n ${CONTAINER_NAME} -t /usr/share/lxc/templates/lxc-download -- --dist debian --release stretch --arch amd64Grant execute permission on container root and related directories to the world:
$ chmod +x ~ ~/.local ~/.local/shareTo start and attach to the container:
$ systemd-run --unit=java --user --scope -p "Delegate=yes" lxc-start -n ${CONTAINER_NAME} -F
$ systemd-run --user --scope -p "Delegate=yes" lxc-attach ${CONTAINER_NAME}Additional Parameters
You can add --server mirrors.tuna.tsinghua.edu.cn/lxc-images to download from mirrors or alternative download servers.
Manage and Delete Containers
Privileged containers are stored at /var/lib/lxc/${NAME} while unprivileged ones are stored at ~/.local/share/lxc. Tools like lxc-ls and lxc-info are oftenly used to manage them.
To delete a container, there is nothing like lxc-delete or lxc-remove, but lxc-destroy.
