Python — PermissionError: [Errno 13] Permission denied on file access

Resolve PermissionError by distinguishing file permission issues from directory, ownership and container boundary problems.

beginnerdebuggingpythonfilesystem

Symptoms

PermissionError: [Errno 13] Permission denied when opening a file
The failure happens on write but reading works
The path works in a shell but fails from the application
The error appears only inside a container or service

Possible causes

The file or its parent directory lacks write or execute permission for the running user
The process runs as a different, unprivileged user than your shell
A mounted volume is read-only or owned by another user
The path is a directory, not a file, so the open mode is wrong

Diagnosis steps

Identify the effective user and target path

id && ls -ld /path/to/file /path/to

Interpretation

The id shows which user runs the process, and ls reveals whether that user can read, write or traverse the path.

Test access with the process user

sudo -u appuser test -w /path/to/file && echo writable

Interpretation

Reproducing the access as the service user confirms whether permissions or the process identity is the cause.

Check mount and container options

mount | grep /path ; docker inspect --format "{{.HostConfig.ReadonlyRootfs}}" container

Interpretation

A read-only mount or read-only root filesystem explains writes that fail despite correct ownership.

Root cause

The effective user for the process cannot perform the requested operation on the path, because permissions, ownership, mount options or the user identity differ from your interactive shell.

Fix

Grant the service user the required permissions on the file and its parent directory, correct ownership, or write to a directory intended for runtime data. For read-only mounts, redirect writes to a writable location.

Verify the fix

Rerun the operation and confirm it succeeds, and check that the created or written file has the expected owner and mode.

Symptom walkthrough

Opening a file for writing raises PermissionError: [Errno 13] Permission denied, while the same path works when you test it manually. The discrepancy is the important clue: your shell and the application may run as different users, or the path may be on a read-only mount. Directories need execute permission for traversal, so a missing x bit on a parent directory can block access even when the file itself looks fine.

Fix in practice

Give the service account the rights the operation requires on the file and each parent directory, fix ownership mismatches, and send runtime writes to a directory designated for them. When the mount is read-only, explicitly redirect writes elsewhere instead of fighting the permissions.

Verification

Repeat the write and confirm it succeeds, then inspect the resulting file to confirm it has the expected owner and mode. A writable test as the service user is the most reliable confirmation.

Diagnostic commands

Check the behavior with commands like these:

id && ls -ld /path/to/file /path/to
sudo -u appuser test -w /path/to/file && echo writable
mount | grep /path ; docker inspect --format "{{.HostConfig.ReadonlyRootfs}}" container