Python PermissionError

What It Means

PermissionError (a subclass of OSError) is raised when an operation is attempted without sufficient filesystem or operating system permissions. The error message reads: [Errno 13] Permission denied: 'filename'. This occurs when trying to read, write, execute, or delete files or directories you don’t have access to.

Common Causes

• Trying to write to a read-only file or directory
• Accessing files owned by root or another user
• Writing to system directories without elevated privileges
• File is locked by another process
• SELinux or AppArmor policies blocking access
• Docker container running as non-root without proper file ownership
• Trying to bind to a privileged port (< 1024) without root access

How to Fix

Check and fix file permissions

# Check current permissions
ls -la /path/to/file

# Fix permissions
chmod 644 /path/to/file      # Read/write for owner, read for others
chmod 755 /path/to/directory  # Includes execute for directories

# Change ownership
sudo chown $USER:$USER /path/to/file

Handle permission errors in code

import os

try:
    with open("/etc/protected_file", "w") as f:
        f.write("data")
except PermissionError:
    # Fall back to a writable location
    fallback_path = os.path.expanduser("~/protected_file")
    with open(fallback_path, "w") as f:
        f.write("data")
    print(f"Written to fallback path: {fallback_path}")

Write to user-accessible directories

import os
from pathlib import Path

# Bad: writing to system directories
with open("/var/log/myapp.log", "w") as f:  # PermissionError
    f.write("log entry")

# Good: write to user-writable paths
log_dir = Path.home() / ".myapp" / "logs"
log_dir.mkdir(parents=True, exist_ok=True)
with open(log_dir / "myapp.log", "a") as f:
    f.write("log entry\n")

# Good: use temp directory
import tempfile
with tempfile.NamedTemporaryFile(mode="w", delete=False) as f:
    f.write("temporary data")
    print(f"Written to: {f.name}")

Check permissions before operating

import os

path = "/path/to/file"

# Check read permission
if os.access(path, os.R_OK):
    with open(path) as f:
        data = f.read()
else:
    print(f"No read permission for {path}")

# Check write permission
if os.access(path, os.W_OK):
    with open(path, "w") as f:
        f.write("data")

# Check directory write permission
dir_path = os.path.dirname(path)
if os.access(dir_path, os.W_OK):
    print("Can write to directory")

Fix in Docker

# Create a non-root user with proper permissions
FROM python:3.12-slim
RUN useradd -m appuser

WORKDIR /app
COPY --chown=appuser:appuser . .

# Create writable directories
RUN mkdir -p /app/data && chown appuser:appuser /app/data

USER appuser
CMD ["python", "app.py"]

Fix port binding issues

# Error: PermissionError: [Errno 13] Permission denied
# when trying to bind to port 80

# Fix: use a non-privileged port (>= 1024)
app.run(host="0.0.0.0", port=8080)

# Or use authbind/setcap to allow binding low ports
# sudo setcap 'cap_net_bind_service=+ep' $(which python3)

Related Errors

• Python FileNotFoundError - File doesn’t exist at all (vs. exists but inaccessible).
• Python ImportError - Module cannot be loaded (may be permission-related for C extensions).