Troubleshooting

Distribution-specific hint

Known limitations

• Only the following storage drivers are supported:
  • overlay2 (only if running with kernel 5.11 or later)
  • fuse-overlayfs (only if running with kernel 4.18 or later, and fuse-overlayfs is installed)
  • btrfs (only if running with kernel 4.18 or later, or ~/.local/share/docker is mounted with user_subvol_rm_allowed mount option)
  • vfs
• cgroup is supported only when running with cgroup v2 and systemd. See Limiting resources.
• Following features are not supported:
  • AppArmor
  • Checkpoint
  • Overlay network
  • Exposing SCTP ports
• To use the ping command, see Routing ping packets.
• To expose privileged TCP/UDP ports (< 1024), see Exposing privileged ports.
• IPAddress shown in docker inspect is namespaced inside RootlessKit's network namespace. This means the IP address is not reachable from the host without nsenter-ing into the network namespace.
• Host network (docker run --net=host) is also namespaced inside RootlessKit.
• NFS mounts as the docker "data-root" is not supported. This limitation is not specific to rootless mode.

Troubleshooting

Unable to install with systemd when systemd is present on the system

$ dockerd-rootless-setuptool.sh install
[INFO] systemd not detected, dockerd-rootless.sh needs to be started manually:
...

rootlesskit cannot detect systemd properly if you switch to your user via sudo su. For users which cannot be logged-in, you must use the machinectl command which is part of the systemd-container package. After installing systemd-container switch to myuser with the following command:

$ sudo machinectl shell myuser@

Where myuser@ is your desired username and @ signifies this machine.

Errors when starting the Docker daemon

[rootlesskit:parent] error: failed to start the child: fork/exec /proc/self/exe: operation not permitted

This error occurs mostly when the value of /proc/sys/kernel/unprivileged_userns_clone is set to 0:

$ cat /proc/sys/kernel/unprivileged_userns_clone
0

To fix this issue, add kernel.unprivileged_userns_clone=1 to /etc/sysctl.conf (or /etc/sysctl.d) and run sudo sysctl --system.

[rootlesskit:parent] error: failed to start the child: fork/exec /proc/self/exe: no space left on device

This error occurs mostly when the value of /proc/sys/user/max_user_namespaces is too small:

$ cat /proc/sys/user/max_user_namespaces
0

To fix this issue, add user.max_user_namespaces=28633 to /etc/sysctl.conf (or /etc/sysctl.d) and run sudo sysctl --system.

[rootlesskit:parent] error: failed to setup UID/GID map: failed to compute uid/gid map: No subuid ranges found for user 1001 ("testuser")

This error occurs when /etc/subuid and /etc/subgid are not configured. See Prerequisites.

could not get XDG_RUNTIME_DIR

This error occurs when $XDG_RUNTIME_DIR is not set.

On a non-systemd host, you need to create a directory and then set the path:

$ export XDG_RUNTIME_DIR=$HOME/.docker/xrd
$ rm -rf $XDG_RUNTIME_DIR
$ mkdir -p $XDG_RUNTIME_DIR
$ dockerd-rootless.sh

Note

You must remove the directory every time you log out.

On a systemd host, log into the host using pam_systemd (see below). The value is automatically set to /run/user/$UID and cleaned up on every logout.

systemctl --user fails with "Failed to connect to bus: No such file or directory"

This error occurs mostly when you switch from the root user to a non-root user with sudo:

# sudo -iu testuser
$ systemctl --user start docker
Failed to connect to bus: No such file or directory

Instead of sudo -iu <USERNAME>, you need to log in using pam_systemd. For example:

• Log in through the graphic console
• ssh <USERNAME>@localhost
• machinectl shell <USERNAME>@

The daemon does not start up automatically

You need sudo loginctl enable-linger $(whoami) to enable the daemon to start up automatically. See Advanced Usage.

docker pull errors

docker: failed to register layer: Error processing tar file(exit status 1): lchown <FILE>: invalid argument

This error occurs when the number of available entries in /etc/subuid or /etc/subgid is not sufficient. The number of entries required vary across images. However, 65,536 entries are sufficient for most images. See Prerequisites.

docker: failed to register layer: ApplyLayer exit status 1 stdout: stderr: lchown <FILE>: operation not permitted

This error occurs mostly when ~/.local/share/docker is located on NFS.

A workaround is to specify non-NFS data-root directory in ~/.config/docker/daemon.json as follows:

{"data-root":"/somewhere-out-of-nfs"}

docker run errors

docker: Error response from daemon: OCI runtime create failed: ...: read unix @->/run/systemd/private: read: connection reset by peer: unknown.

This error occurs on cgroup v2 hosts mostly when the dbus daemon is not running for the user.

$ systemctl --user is-active dbus
inactive

$ docker run hello-world
docker: Error response from daemon: OCI runtime create failed: container_linux.go:380: starting container process caused: process_linux.go:385: applying cgroup configuration for process caused: error while starting unit "docker
-931c15729b5a968ce803784d04c7421f791d87e5ca1891f34387bb9f694c488e.scope" with properties [{Name:Description Value:"libcontainer container 931c15729b5a968ce803784d04c7421f791d87e5ca1891f34387bb9f694c488e"} {Name:Slice Value:"use
r.slice"} {Name:PIDs Value:@au [4529]} {Name:Delegate Value:true} {Name:MemoryAccounting Value:true} {Name:CPUAccounting Value:true} {Name:IOAccounting Value:true} {Name:TasksAccounting Value:true} {Name:DefaultDependencies Val
ue:false}]: read unix @->/run/systemd/private: read: connection reset by peer: unknown.

To fix the issue, run sudo apt-get install -y dbus-user-session or sudo dnf install -y dbus-daemon, and then relogin.

If the error still occurs, try running systemctl --user enable --now dbus (without sudo).

--cpus, --memory, and --pids-limit are ignored

This is an expected behavior on cgroup v1 mode. To use these flags, the host needs to be configured for enabling cgroup v2. For more information, see Limiting resources.

Networking errors

This section provides troubleshooting tips for networking in rootless mode.

Networking in rootless mode is supported via network and port drivers in RootlessKit. Network performance and characteristics depend on the combination of network and port driver you use. If you're experiencing unexpected behavior or performance related to networking, review the following table which shows the configurations supported by RootlessKit, and how they compare:

For information about troubleshooting specific networking issues, see:

• docker run -p fails with cannot expose privileged port
• Ping doesn't work
• IPAddress shown in docker inspect is unreachable
• --net=host doesn't listen ports on the host network namespace
• Network is slow
• docker run -p does not propagate source IP addresses

docker run -p fails with cannot expose privileged port

docker run -p fails with this error when a privileged port (< 1024) is specified as the host port.

$ docker run -p 80:80 nginx:alpine
docker: Error response from daemon: driver failed programming external connectivity on endpoint focused_swanson (9e2e139a9d8fc92b37c36edfa6214a6e986fa2028c0cc359812f685173fa6df7): Error starting userland proxy: error while calling PortManager.AddPort(): cannot expose privileged port 80, you might need to add "net.ipv4.ip_unprivileged_port_start=0" (currently 1024) to /etc/sysctl.conf, or set CAP_NET_BIND_SERVICE on rootlesskit binary, or choose a larger port number (>= 1024): listen tcp 0.0.0.0:80: bind: permission denied.

When you experience this error, consider using an unprivileged port instead. For example, 8080 instead of 80.

$ docker run -p 8080:80 nginx:alpine

To allow exposing privileged ports, see Exposing privileged ports.

Ping doesn't work

Ping does not work when /proc/sys/net/ipv4/ping_group_range is set to 1 0:

$ cat /proc/sys/net/ipv4/ping_group_range
1       0

For details, see Routing ping packets.

IPAddress shown in docker inspect is unreachable

This is an expected behavior, as the daemon is namespaced inside RootlessKit's network namespace. Use docker run -p instead.

--net=host doesn't listen ports on the host network namespace

This is an expected behavior, as the daemon is namespaced inside RootlessKit's network namespace. Use docker run -p instead.

Network is slow

Docker with rootless mode uses slirp4netns as the default network stack if slirp4netns v0.4.0 or later is installed. If slirp4netns is not installed, Docker falls back to VPNKit. Installing slirp4netns may improve the network throughput.

For more information about network drivers for RootlessKit, see RootlessKit documentation.

Also, changing MTU value may improve the throughput. The MTU value can be specified by creating ~/.config/systemd/user/docker.service.d/override.conf with the following content:

[Service]
Environment="DOCKERD_ROOTLESS_ROOTLESSKIT_MTU=<INTEGER>"

And then restart the daemon:

$ systemctl --user daemon-reload
$ systemctl --user restart docker

docker run -p does not propagate source IP addresses

This is because Docker in rootless mode uses RootlessKit's builtin port driver by default, which doesn't support source IP propagation. To enable source IP propagation, you can:

• Use the slirp4netns RootlessKit port driver
• Use the pasta RootlessKit network driver, with the implicit port driver

The pasta network driver is experimental, but provides improved throughput performance compared to the slirp4netns port driver. The pasta driver requires Docker Engine version 25.0 or later.

To change the RootlessKit networking configuration:

1. Create a file at ~/.config/systemd/user/docker.service.d/override.conf.

2. Add the following contents, depending on which configuration you would like to use:

   • slirp4netns

     [Service]
     Environment="DOCKERD_ROOTLESS_ROOTLESSKIT_NET=slirp4netns"
     Environment="DOCKERD_ROOTLESS_ROOTLESSKIT_PORT_DRIVER=slirp4netns"

   • pasta network driver with implicit port driver

     [Service]
     Environment="DOCKERD_ROOTLESS_ROOTLESSKIT_NET=pasta"
     Environment="DOCKERD_ROOTLESS_ROOTLESSKIT_PORT_DRIVER=implicit"

3. Restart the daemon:

   $ systemctl --user daemon-reload
   $ systemctl --user restart docker
   

For more information about networking options for RootlessKit, see:

• Network drivers
• Port drivers

Tips for debugging

Entering into dockerd namespaces

The dockerd-rootless.sh script executes dockerd in its own user, mount, and network namespaces.

For debugging, you can enter the namespaces by running nsenter -U --preserve-credentials -n -m -t $(cat $XDG_RUNTIME_DIR/docker.pid).

Uninstall

To remove the systemd service of the Docker daemon, run dockerd-rootless-setuptool.sh uninstall:

$ dockerd-rootless-setuptool.sh uninstall
+ systemctl --user stop docker.service
+ systemctl --user disable docker.service
Removed /home/testuser/.config/systemd/user/default.target.wants/docker.service.
[INFO] Uninstalled docker.service
[INFO] This uninstallation tool does NOT remove Docker binaries and data.
[INFO] To remove data, run: `/usr/bin/rootlesskit rm -rf /home/testuser/.local/share/docker`

Unset environment variables PATH and DOCKER_HOST if you have added them to ~/.bashrc.

To remove the data directory, run rootlesskit rm -rf ~/.local/share/docker.

To remove the binaries, remove docker-ce-rootless-extras package if you installed Docker with package managers. If you installed Docker with https://get.docker.com/rootless (Install without packages), remove the binary files under ~/bin:

$ cd ~/bin
$ rm -f containerd containerd-shim containerd-shim-runc-v2 ctr docker docker-init docker-proxy dockerd dockerd-rootless-setuptool.sh dockerd-rootless.sh rootlesskit rootlesskit-docker-proxy runc vpnkit