If a Linux-build-server suddenly starts getting slow, you will check for the following three things
Application Level troubleshooting: RAM related issues, Disk I/O read write issues, Disk Space related Issues, etc.
System-Level troubleshooting: Check for Application log file OR application server log file, system performance issues, Web Server Log – check HTTP, tomcat log, etc. or check JBoss, WebLogic logs to see if the application server response/receive time is the issues for slowness, Memory Leak of any application
Dependent Services troubleshooting: Antivirus related issues, Firewall related issues, Network issues, SMTP server response time issues, etc.