Troubleshooting High CPU Usage During SSH Sessions

High CPU usage during SSH sessions can be attributed to several factors. Here are some potential causes and solutions to help mitigate the issue:

Potential Causes

1. Encryption Overhead: SSH uses encryption, which can be CPU-intensive. If your CPU is older or under heavy load from other processes, this can lead to high CPU usage during SSH sessions.
2. Large Data Transfers: Transferring large files over SSH (using tools like scp or rsync) can consume significant CPU resources, particularly if the encryption algorithms are demanding.
3. SSH Key Size: The modulus size of your SSH keys can impact performance. Using larger keys (e.g., 2048 bits or higher) increases the computational load.
4. Background Processes: Other processes running on the server may be consuming CPU resources, leaving less available for handling SSH connections.
5. Network Management Systems (NMS): If an NMS is monitoring your switch or server during SSH sessions, it may flag high CPU usage due to the additional load from SSH traffic.

Solutions

1. Optimize SSH Configuration:
   • Consider using a less CPU-intensive encryption algorithm (e.g., blowfish instead of aes256).
   • Adjust the key size to a more manageable level (e.g., 1024 bits) if security requirements allow.
2. Monitor Background Processes: Use tools like top or htop to identify any processes that are consuming excessive CPU resources and terminate them if necessary.
3. Increase Hardware Resources: If possible, upgrading your server's CPU or increasing RAM can alleviate bottlenecks caused by high load.
4. Limit Data Transfer Size: When transferring files, consider splitting large transfers into smaller chunks or using multi-threaded tools that can better utilize available CPU resources.
5. Adjust NMS Settings: If NMS is causing false positives for high CPU usage during SSH sessions, consider adjusting its thresholds or settings to reduce unnecessary alerts.

By addressing these areas, you should be able to reduce the high CPU usage experienced during SSH sessions and improve overall system performance.