`dockerd-rootless.sh` fails on systems with IPv6 disabled

[acuD1]

The dockerd-rootless.sh script unconditionally attempts to enable IPv6 forwarding via sysctl -w net.ipv6.conf.all.forwarding=1, which causes rootless Docker installation to fail on systems where IPv6 is intentionally disabled for security hardening.

When running dockerd-rootless-setuptool.sh install on a system with IPv6 disabled at the kernel level, the installation fails with:

sysctl: cannot stat /proc/sys/net/ipv6/conf/all/forwarding: No such file or directory
[rootlesskit:child ] error: command [/usr/bin/dockerd-rootless.sh] exited: exit status 1

Expected Behavior

The script should either:

1. Gracefully handle the case where IPv6 is disabled (skip the IPv6 sysctl or treat errors as non-fatal)
2. Provide an environment variable (e.g., DOCKERD_ROOTLESS_DISABLE_IPV6=true) to skip IPv6 configuration
3. Check if IPv6 is available before attempting to configure it

Relevant Code

In /usr/bin/dockerd-rootless.sh (lines 242-243):

sysctl -w net.ipv4.ip_forward=1
sysctl -w net.ipv6.conf.all.forwarding=1

The IPv4 line succeeds, but the IPv6 line causes a fatal error when IPv6 is disabled.

Proposed Solution

Change line 243 to:

sysctl -w net.ipv6.conf.all.forwarding=1 2>/dev/null || true

Or add a conditional check:

if [ -f /proc/sys/net/ipv6/conf/all/forwarding ]; then
    sysctl -w net.ipv6.conf.all.forwarding=1
fi

Environment

• Docker version: 28.x (latest)
• OS: Ubuntu 24.04 (affects all Linux distributions)
• Installation method: docker-ce-rootless-extras package
• IPv6 status: Disabled via kernel parameter or sysctl

Additional Context

The Docker daemon configuration supports "ipv6": false in daemon.json, so there's already precedent for supporting IPv6-disabled environments at the daemon level. The rootless setup script should respect this same principle.

[AkihiroSuda]

Proposed Solution

Do you plan to submit a PR?
https://github.com/moby/moby/blob/master/contrib/dockerd-rootless.sh

[AkihiroSuda]

Seem fixed in:

• rootless: ignore error when enabling IPv6 forwarding moby/moby#51542

[acuD1]

@AkihiroSuda Ah yes it has been fixed nice ! I Close the issue