Checking for free resources
htop is a very useful command for monitoring overall server utilization (please see man htop for full details)
On the command line type:
By default at the top of the screen you will see a set of bar graphs representing the load on each CPU thread letting you see how busy they all are. Memory utilization is shown just below along with the number of tasks, and the system load average.
From this information you should be able to quickly see whether the system has enough spare capacity to run your job, assuming you have some idea about the resources required.
On the remainder of the page htop displays all the active processes, with who is running them, cpu and memory usage, and the command itself.