**🚨 Common Linux Server Issues & Quick Fixes 🚨**
As a sysadmin or DevOps engineer, managing Linux servers can be challenging. Here’s a list of common issues and commands to resolve them efficiently:
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### **1. Disk Space Running Out**
**Fix**:
- Check disk usage: `df -h`
- Find large files: `du -sh /var/* | sort -rh`
- Clean temp files: `sudo rm -rf /tmp/*`
---
### **2. High CPU Usage**
**Fix**:
- Monitor CPU usage: `top`
- Terminate problematic process: `kill <PID>`
- Analyze processes: `ps aux --sort=-%cpu`
---
### **3. Memory Issues**
**Fix**:
- Check memory usage: `free -h`
- Identify memory-hogging processes: `ps aux --sort=-%mem`
- Clear cache: `echo 3 > /proc/sys/vm/drop_caches`
---
### **4. Service Unavailable**
**Fix**:
- Check service status: `sudo systemctl status <service>`
- Restart service: `sudo systemctl restart <service>`
- Check logs: `sudo journalctl -u <service>`
---
### **5. Network Problems**
**Fix**:
- Test connectivity: `ping <ip>`
- Check open connections: `netstat -tuln`
- Verify firewall rules: `sudo ufw status`
---
### **6. Permission Errors**
**Fix**:
- Check permissions: `ls -l <file>`
- Modify permissions: `sudo chmod 755 <file>`
- Change ownership: `sudo chown user:group <file>`
---
### **7. Update Failures**
**Fix**:
- Clear package cache: `sudo apt clean`
- Fix broken packages: `sudo apt --fix-broken install`
- Update system: `sudo apt update && sudo apt upgrade -y`
---
### **8. Logs Consuming Space**
**Fix**:
- Compress logs: `sudo tar -czvf logs_archive.tar.gz /var/log/`
- Configure log rotation: `sudo nano /etc/logrotate.conf`
---
### **9. SSH Access Issues**
**Fix**:
- Check SSH status: `sudo systemctl status sshd`
- Restart SSH: `sudo systemctl restart sshd`
- Check logs: `sudo tail -f /var/log/auth.log`
---
### **10. DNS Resolution Failure**
**Fix**:
- Check DNS config: `cat /etc/resolv.conf`
- Test DNS resolution: `nslookup google.com`
- Restart network: `sudo systemctl restart networking`
---
### **11. Time Synchronization Issues**
**Fix**:
- Check time sync status: `timedatectl status`
- Manually sync time: `sudo ntpdate pool.ntp.org`
- Restart NTP service: `sudo systemctl restart ntp`
---
### **12. Corrupted Filesystem**
**Fix**:
- Check filesystem integrity: `sudo fsck /dev/sdX`
- Reinstall critical packages: `sudo apt-get install --reinstall coreutils`
---
### **13. User Quota Exceeded**
**Fix**:
- Check quotas: `repquota -a`
- Modify user quotas: `edquota -u <username>`
---
### **14. Zombie Processes**
**Fix**:
- Identify zombie processes: `ps aux | grep 'Z'`
- Kill parent process: `kill -9 <PPID>`
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