• For Nvidia GPUs there is a tool nvidia-smi that can show memory
  usage, GPU utilization and temperature of GPU.


• For Intel GPU's you can use the intel-gpu-tools.



• AMD has two options

  
  
  
  
  

  1. fglrx (closed source drivers):

     
     
     

     aticonfig --odgc --odgt
     
     

  
  
  2. And for mesa (open source drivers), you can use RadeonTop .
  
  

^{Source:GPU usage monitoring}