Introduction

Linux servers are widely used for web hosting, databases, and enterprise applications due to their stability, security, and cost-effectiveness.
However, even experienced sysadmins encounter server issues—from permission errors to network connectivity problems.

In this guide, we’ll explore:

• ⚙️ Key Linux file permissions: chmod, chown, and Access Control Lists (ACLs)
• Common server issues and step-by-step solutions
• ️ Troubleshooting best practices

Understanding Linux Permissions: chmod, chown, and ACLs

Why Permissions Matter

Linux permissions protect files, directories, and system resources from unauthorized access, modifications, or deletions.

1. chmod (Change Mode)

The chmod command modifies file permissions based on three user classes:

• Owner (u)
• Group (g)
• Others (o)

Permission Types:

• Read (r) = 4
• ✏️ Write (w) = 2
• ️ Execute (x) = 1

️ Basic chmod Syntax:

chmod [permissions] [file/directory]
        

⚙️ Example 1: Assign Permissions Using Octal Notation

chmod 755 script.sh
        

Explanation:

• 7 (rwx): Owner – read, write, execute.
• 5 (r-x): Group – read, execute.
• 5 (r-x): Others – read, execute.

⚙️ Example 2: Assign Permissions Using Symbolic Notation

chmod u+x script.sh
        

Explanation: Adds execute permission to the file owner.

2. chown (Change Owner)

The chown command changes the ownership of files and directories.

️ Basic chown Syntax:

chown [owner][:group] [file/directory]
        

⚙️ Example 1: Change File Ownership

chown john:developers report.txt
        

Explanation: Changes file ownership to user john and group developers.

⚙️ Example 2: Recursively Change Directory Ownership

chown -R nginx:www-data /var/www/html
        

Explanation: Applies changes to all files and subdirectories.

3. Access Control Lists (ACLs)

ACLs provide granular permissions beyond the standard owner/group/others model.

️ Common ACL Commands:

# Set ACL for user john
setfacl -m u:john:rwx file.txt
# View ACL
getfacl file.txt
# Remove ACL for user john
setfacl -x u:john file.txt
        

Example: Grants john read, write, and execute permissions.

️ Linux Server Troubleshooting: Common Issues and Fixes

bash: ./backup.sh: Permission denied
            

ping google.com
ping: unknown host google.com
            

No space left on device
            

Troubleshooting Best Practices

• ✅ Document Everything: Track all configuration changes and fixes.
• Monitor System Health: Use tools like Nagios and Zabbix.
• Follow Least Privilege Principle: Limit access permissions.
• ⚙️ Regularly Update Software: Apply patches promptly.
• Automate Backups: Schedule regular backups and test them periodically.

Conclusion: Mastering Linux Troubleshooting

Linux server troubleshooting requires a combination of , problem-solving skills, and experience.
By understanding chmod, chown, and ACLs, you’ll be better equipped to handle common issues effectively.

Key Takeaways:

• Master file permissions: chmod, chown, and ACLs are essential for server security.
• ️ Adopt proactive monitoring: Detect issues early with tools like Prometheus and Nagios.
• Document changes: Maintain logs of all server modifications and fixes.