When attempting to restart Nginx, you might encounter permission-related errors preventing the service from functioning properly. The key symptoms include:

Restarting nginx: [alert]: could not open error log file: open() "/var/log/nginx/error.log" failed (13: Permission denied)
2011/02/16 17:20:58 [warn] 23925#0: the "user" directive makes sense only if the master process runs with super-user privileges
2011/02/16 17:20:58 [emerg] 23925#0: open() "/var/run/nginx.pid" failed (13: Permission denied)

The root cause lies in incorrect file ownership and permissions. Nginx requires proper access to:

• /var/log/nginx/ directory and its contents
• /var/run/nginx.pid file
• Configuration files in /etc/nginx/

First, check current permissions:

ls -la /var/log/nginx/
ls -la /var/run/nginx.pid
ls -la /etc/nginx/nginx.conf

Here's how to resolve the permission issues:

# 1. Create necessary directories if they don't exist
sudo mkdir -p /var/log/nginx /var/run/nginx

# 2. Set correct ownership (assuming nginx runs as www-data)
sudo chown -R www-data:www-data /var/log/nginx
sudo chown -R www-data:www-data /var/run/nginx

# 3. Set proper permissions
sudo chmod -R 755 /var/log/nginx
sudo chmod -R 755 /var/run/nginx

# 4. For the PID file specifically
sudo touch /var/run/nginx.pid
sudo chown www-data:www-data /var/run/nginx.pid

Ensure your /etc/nginx/nginx.conf has the correct user directive:

user www-data;
worker_processes auto;
pid /var/run/nginx.pid;

For systems with SELinux enabled, you may need additional steps:

# Check SELinux context
ls -Z /var/log/nginx/

# Fix context if needed
sudo chcon -R -t httpd_log_t /var/log/nginx/
sudo restorecon -Rv /var/log/nginx/

After making these changes:

sudo nginx -t  # Test configuration
sudo systemctl restart nginx  # Restart service
sudo systemctl status nginx  # Check status

For production environments, consider creating a systemd service override to handle permissions at startup:

# Create override directory
sudo mkdir -p /etc/systemd/system/nginx.service.d/

# Create override file
cat <
After fixing the Nginx service, verify CSS and other static files are loading properly:
curl -I http://yoursite.com/style.css

Ensure static files have correct permissions (typically 644) and are owned by the appropriate user.

When attempting to restart Nginx, you're likely encountering multiple permission-related errors that cascade into service failure. The key symptoms include:
1. Error log access denied: "/var/log/nginx/error.log" failed (13: Permission denied)
2. PID file creation failure: "/var/run/nginx.pid" failed (13: Permission denied)
3. User directive warning when running without root privileges

The root cause typically stems from incorrect ownership or permissions on critical Nginx directories. Let's examine the essential paths:
ls -ld /var/log/nginx/
ls -ld /var/run/
ls -ld /etc/nginx/

Common problematic scenarios include:

Nginx running as non-root user without proper directory access
Mixed ownership between root and www-data (or custom user)
SELinux/AppArmor restrictions (particularly on CentOS/RHEL)

1. Correct Directory Permissions
Execute these commands to fix common permission issues:
sudo chown -R root:nginx /var/log/nginx/
sudo chmod -R 770 /var/log/nginx/
sudo chown -R root:nginx /var/run/
sudo touch /var/run/nginx.pid
sudo chown nginx:nginx /var/run/nginx.pid

2. Configuration File Adjustments
Edit your nginx.conf to ensure proper user directives:
user nginx;
worker_processes auto;
error_log /var/log/nginx/error.log;
pid /var/run/nginx.pid;

3. SELinux Context Fix (For RHEL-based Systems)
sudo chcon -Rt httpd_log_t /var/log/nginx/
sudo semanage fcontext -a -t httpd_log_t "/var/log/nginx(/.*)?"
sudo restorecon -Rv /var/log/nginx

If issues persist, use these diagnostic commands:
# Check running processes
ps aux | grep nginx

# Verify effective permissions
sudo -u nginx ls -l /var/log/nginx/error.log

# Check audit logs (for SELinux)
ausearch -m avc -ts recent

Implement these practices to avoid future issues:
# Create systemd service override
sudo systemctl edit nginx

[Service]
ExecStartPre=/bin/mkdir -p /var/run/nginx
ExecStartPre=/bin/chown -R nginx:nginx /var/run/nginx
ExecStartPre=/bin/chmod -R 755 /var/run/nginx