Fix: Linux Permission Denied Errors

!Symptoms

• Command fails with 'Permission denied'
• Cannot read, write, or execute a file despite it existing
• SSH connection refused with 'Permission denied (publickey)'
• Scripts fail with permission errors when run by a service account

?Root Causes

• File ownership does not match the running user
• File permissions (chmod) are too restrictive
• SELinux or AppArmor blocking the action
• SSH key permissions too open (must be 600)
• Trying to bind to a privileged port (< 1024) without root
• sudo not configured for the user

#Diagnosis Steps

1. 1Check file permissions: `ls -la <file>`
2. 2Check current user: `whoami` and `id`
3. 3Check SELinux status: `getenforce` and `ls -laZ <file>`
4. 4For SSH: check key permissions `ls -la ~/.ssh/` (should be 700 for .ssh, 600 for keys)
5. 5Check sudo access: `sudo -l`

>Fix

1. 1Fix ownership: `chown <user>:<group> <file>`
2. 2Fix permissions: `chmod 644 <file>` for files, `chmod 755 <dir>` for directories
3. 3For SSH keys: `chmod 600 ~/.ssh/id_rsa && chmod 644 ~/.ssh/id_rsa.pub`
4. 4Fix SELinux context: `restorecon -Rv <path>`
5. 5For port binding: use a port > 1024 or grant capability: `setcap 'cap_net_bind_service=+ep' <binary>`

*Prevention

• Follow the principle of least privilege for file permissions
• Use groups to manage access instead of changing ownership frequently
• Document required permissions in deployment runbooks
• Use ansible/chef/puppet to enforce consistent permissions
• Set umask appropriately for service accounts

Related Error Messages