RootlessKit: Linux-native fakeroot using user namespaces
RootlessKit is a Linux-native implementation of “fake root” using user_namespaces(7).
The purpose of RootlessKit is to run Docker and Kubernetes as an unprivileged user (known as “Rootless mode”), so as to protect the real root on the host from potential container-breakout attacks.
What RootlessKit actually does
RootlessKit creates user_namespaces(7) and mount_namespaces(7),
and executes newuidmap(1)/newgidmap(1) along with subuid(5) and subgid(5).
RootlessKit also supports isolating network_namespaces(7) with userspace NAT using “slirp”.
Kernel-mode NAT using SUID-enabled lxc-user-nic(1) is also experimentally supported.
Similar projects
Tools based on LD_PRELOAD (not enough to run rootless containers and yet lacks support for static binaries):
Tools based on ptrace(2) (not enough to run rootless containers and yet slow):
Tools based on user_namespaces(7) (as in RootlessKit, but without support for --copy-up, --net, …):
Projects using RootlessKit
Container engines:
Container image builders:
- BuildKit: Next-generation
docker build backend
Kubernetes distributions:
- Usernetes: Docker & Kubernetes, installable under a non-root user’s
$HOME.
- k3s: Lightweight Kubernetes
Setup
Run make && sudo make install .
The following binaries will be installed:
/usr/local/bin/rootlesskit/usr/local/bin/rootlessctl/usr/local/bin/rootlesskit-docker-proxy (DEPRECATED; Only required for Docker prior to v28)
Requirements
subuid
-
newuidmap and newgidmap need to be installed on the host. These commands are provided by the uidmap package on most distributions.
-
/etc/subuid and /etc/subgid should contain more than 65536 sub-IDs. e.g. penguin:231072:65536. These files are automatically configured on most distributions.
$ id -u
1001
$ whoami
penguin
$ grep "^$(whoami):" /etc/subuid
penguin:231072:65536
$ grep "^$(whoami):" /etc/subgid
penguin:231072:65536
See also https://rootlesscontaine.rs/getting-started/common/subuid/
sysctl
Old distros may require setting up sysctl such as kernel.unprivileged_userns_clone=1:
See https://rootlesscontaine.rs/getting-started/common/sysctl/.
AppArmor
On Ubuntu 24.04 or later, the rootlesskit binary is expected to be exactly under /usr/bin.
To install rootlesskit on other paths such as /usr/local/bin, you need to install a custom AppArmor profile.
See https://rootlesscontaine.rs/getting-started/common/apparmor/.
Usage
Inside rootlesskit bash, your UID is mapped to 0 but it is not the real root:
(host)$ rootlesskit bash
(rootlesskit)# id
uid=0(root) gid=0(root) groups=0(root),65534(nogroup)
(rootlesskit)# ls -l /etc/shadow
-rw-r----- 1 nobody nogroup 1050 Aug 21 19:02 /etc/shadow
(rootlesskit)# cat /etc/shadow
cat: /etc/shadow: Permission denied
Environment variables are kept untouched:
(host)$ rootlesskit bash
(rootlesskit)# echo $USER
penguin
(rootlesskit)# echo $HOME
/home/penguin
(rootlesskit)# echo $XDG_RUNTIME_DIR
/run/user/1001
Filesystems can be isolated from the host with --copy-up:
(host)$ rootlesskit --copy-up=/etc bash
(rootlesskit)# rm /etc/resolv.conf
(rootlesskit)# vi /etc/resolv.conf
You can even create network namespaces with Slirp:
(host)$ rootlesskit --copy-up=/etc --copy-up=/run --net=slirp4netns --disable-host-loopback bash
(rootleesskit)# ip netns add foo
...
Full CLI options
$ rootlesskit --help
NAME:
rootlesskit - Linux-native fakeroot using user namespaces
USAGE:
rootlesskit [global options] [arguments...]
VERSION:
3.1.0
DESCRIPTION:
RootlessKit is a Linux-native implementation of "fake root" using user_namespaces(7).
Web site: https://github.com/rootless-containers/rootlesskit
Examples:
# spawn a shell with a new user namespace and a mount namespace
rootlesskit bash
# make /etc writable
rootlesskit --copy-up=/etc bash
# set mount propagation to rslave
rootlesskit --propagation=rslave bash
# create a network namespace with slirp4netns, and expose 80/tcp on the namespace as 8080/tcp on the host
rootlesskit --copy-up=/etc --net=slirp4netns --disable-host-loopback --port-driver=builtin -p 127.0.0.1:8080:80/tcp bash
Note: RootlessKit requires /etc/subuid and /etc/subgid to be configured by the real root user.
See https://rootlesscontaine.rs/getting-started/common/ .
OPTIONS:
Misc:
--debug debug mode (default: false)
--print-semver value print a version component as a decimal integer [major, minor, patch]
--help, -h show help
--version, -v print the version
Mount:
--copy-up value [ --copy-up value ] mount a filesystem and copy-up the contents. e.g. "--copy-up=/etc" (typically required for non-host network)
--copy-up-mode value copy-up mode [tmpfs+symlink] (default: "tmpfs+symlink")
--propagation value mount propagation [rprivate, rslave] (default: "rprivate")
Network:
--net value network driver [host, none, pasta(experimental), slirp4netns, vpnkit, lxc-user-nic(experimental), gvisor-tap-vsock(experimental)] (default: "host")
--mtu value MTU for non-host network (default: 65520 for pasta and slirp4netns, 1500 for others) (default: 0)
--cidr value CIDR for pasta, slirp4netns and gvisor-tap-vsock networks (default: 10.0.2.0/24)
--ifname value Network interface name (default: tap0 for pasta, slirp4netns, and vpnkit; eth0 for lxc-user-nic)
--disable-host-loopback prohibit connecting to 127.0.0.1:* on the host namespace (default: false)
--ipv6 enable IPv6 routing. Unrelated to port forwarding. Only supported for pasta and slirp4netns. (experimental) (default: false)
--detach-netns detach network namespaces (default: false)
Network [lxc-user-nic]:
--lxc-user-nic-binary value path of lxc-user-nic binary for --net=lxc-user-nic (default: "/usr/libexec/lxc/lxc-user-nic")
--lxc-user-nic-bridge value lxc-user-nic bridge name (default: "lxcbr0")
Network [pasta]:
--pasta-binary value path of pasta binary for --net=pasta (default: "pasta")
--pesto-binary value path of pesto binary for --port-driver=pesto (default: "pesto")
Network [slirp4netns]:
--slirp4netns-binary value path of slirp4netns binary for --net=slirp4netns (default: "slirp4netns")
--slirp4netns-sandbox value enable slirp4netns sandbox (experimental) [auto, true, false] (the default is planned to be "auto" in future) (default: "false")
--slirp4netns-seccomp value enable slirp4netns seccomp (experimental) [auto, true, false] (the default is planned to be "auto" in future) (default: "false")
Network [vpnkit]:
--vpnkit-binary value path of VPNKit binary for --net=vpnkit (default: "vpnkit")
Port:
--port-driver value
提示：代码过长已自动截断
State directory
The following files will be created in the state directory, which can be specified with --state-dir:
lock: lock filechild_pid: decimal PID text that can be used for nsenter(1).api.sock: REST API socket. See ./docs/api.md and ./docs/port.md.netns (since v2.0.0): Detached NetNS. Created only with --detach-netns. Valid only in the child mount namespace.resolv.conf (since v2.0.0): resolv.conf file. Bind-mounted to /etc/resolv.conf unles --detach-netns is specified.hosts (since v2.0.0): hosts file. Bind-mounted to /etc/hosts unless --detach-netns is specified.
If --state-dir is not specified, RootlessKit creates a temporary state directory on /tmp and removes it on exit.
Undocumented files are subject to change.
Environment variables
The following environment variables will be set for the child process:
ROOTLESSKIT_STATE_DIR (since v0.3.0): absolute path to the state dirROOTLESSKIT_PARENT_EUID (since v0.8.0): effective UIDROOTLESSKIT_PARENT_EGID (since v0.8.0): effective GID
Undocumented environment variables are subject to change.
Additional documents
./docs/network.md: Networking (--net, --mtu, --cidr, --disable-host-loopback, --slirp4netns-*, …)./docs/port.md: Port forwarding (--port-driver, -p, …)./docs/mount.md: Mount (--propagation, …)./docs/process.md: Process (--pidns, --reaper, --cgroupns, --evacuate-cgroup2, …)./docs/api.md: REST API./docs/subid.md: Sub UIDs and sub GIDs
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