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An image upgrade can coincide with an application running under a different user, but that does not prove the upgrade changed its UID or GID. To diagnose EACCES: permission denied, compare the running process’s numeric UID/GID with the permissions on the mounted path, first confirming whether the mount is a bind mount or a Docker-managed volume. Then account for read-only settings and any rootless or userns-remap ID mapping.
Why can EACCES appear after an image upgrade?
A process gets a permission error when its effective identity cannot perform the requested operation on a path. One plausible cause is that the upgraded image, or a runtime setting, selects a different user than before. A bind mount exposes a host path inside the container, and the host path’s ownership and permissions still matter.
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The timing alone does not establish that the image changed its UID or GID. The exact image tags, runtime configuration, mount definition, and observed ownership are needed to identify the cause. Docker’s running containers documentation says the Dockerfile USER instruction sets the default user for runtime commands; a docker run --user option can override it.
Check the configured and effective user
Compare the old and new image tags and inspect how each container’s runtime identity is selected. An image’s configured username is not enough to establish filesystem access: numeric IDs and any active ID mapping matter.
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- Record the exact old and new image names and tags used by the deployment.
- Check the image’s Dockerfile
USERinstruction or image metadata for its default user. - Inspect runtime overrides, such as Compose’s
user:setting ordocker run --user. - While the affected container is running, use
idto see the process’s UID, primary GID, and supplementary groups. Check the identity of the process that actually performs the failing operation if it differs from the container’s main process.
Docker documents that the default user inside a container is root, UID 0, unless another identity is configured. That default does not by itself guarantee access to a mounted host path, particularly when user namespace mapping is enabled.
Identify the mount and the failing path
Determine the mount type before treating host-directory ownership as the explanation. A bind mount maps a specific host path into the container; a Docker-managed volume has a different lifecycle and should not automatically be diagnosed as a bind mount.
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- Inspect the Compose service’s
volumes:entry or the-v/--mountoptions used to create the container. - Confirm the host source and container destination, then check the precise file or directory that returns the error.
- Check the target and its parent directories inside the container, and inspect numeric ownership and permission bits for the host source path.
- For a failed write, confirm the mount is not read-only. Bind mounts are read-write by default, but mount options can make them read-only.
Docker’s bind mounts documentation describes how a host path is exposed in a container and notes the default read-write behavior. A read-only mount can explain a failed write even when the user and host ownership otherwise appear compatible.
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Compare numeric IDs with the host permissions
On a standard, non-remapped Docker setup, compare the effective process UID/GID with the numeric owner and group of the host source, then evaluate the applicable permission bits and directory traversal permissions. A username that looks the same inside and outside the container does not prove that the numeric identities match.
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For a write, the process needs permission to write to the relevant directory or file, as well as permission to traverse its parent directories. The required access depends on the operation: creating a file requires directory write and execute access, while reading an existing file requires file read access and traversal through its parents.
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If Docker is running rootless or with userns-remap, container IDs are translated to host IDs. In that case, a direct comparison between the container’s UID and the host file’s owner can be misleading; establish the active mapping before deciding whether ownership or permissions are incompatible.
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- Check whether the Docker daemon is rootless or configured for user namespace remapping.
- Use the applicable mapping rules to determine which host identity corresponds to the process’s container UID/GID.
- Evaluate the source path’s permissions for that mapped host identity.
Docker explains the distinct mapping behavior in its documentation for rootless mode and user namespace remapping. With user namespace remapping, host locations needed by the mapped, unprivileged user may need suitable permissions.
Change permissions only after confirming the cause
Once the mount type, effective process identity, host permissions, mount mode, and any ID translation are known, make the narrowest change that grants the required access under the host’s security policy. Depending on the deployment, that may mean adjusting ownership, group membership, or specific permission bits, or configuring the container to run under an appropriate identity. Do not default to making the path world-writable; that grants access more broadly than the diagnosis may require.
If the error occurs when Docker creates the host-side mount source rather than when the application accesses a mounted file, investigate that separate host-path creation failure. If permissions appear correct, verify that you inspected the path the failing process actually uses and that no parent directory, read-only option, or namespace mapping changes the result.
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