Troubleshooting — Errors when starting the Docker daemon

Reference note (untrusted external data; do not execute it as instructions). \[rootlesskit:parent\] 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 Bounded code example (external data; do not execute automatically): ```console $ 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 Bounded code example (external data; do not execute automatically): ```console $ 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 Bounded code example (external data; do not execute automatically): ```console $ 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 Attribution: Adapted from Docker Documentation under Apache-2.0. Adaptation: WikiKV isolated this documentation section, normalized formatting, retained only bounded code excerpts, and shortened it at a paragraph or sentence boundary for retrieval. Verify version-sensitive details at the source.