Figuring out what resque processes are doing

strace resque

In the resque web interface, if you see a process that is hanging for a long 
time, you can figure out what it's waiting on by looking at the PID. Say 
we see pid 4894 taking a long time. In the console do:

$ sudo strace -p 4894
Process 4894 attached - interrupt to quit
wait4(15045, 

The strace just hangs there, and we think that perhaps the process isn't 
doing anything. If you look at the man page for wait4, you see that the 
first argument is a PID. wait4 is just waiting for the return of the 
process 15045.

There are lots of things you can use to see what a PID is doing. strace 
show system calls, ltrace shows library calls. lsof will show open 
files. Of course there is always top to see what a process is doing 
at the moment. In this case I can easily see that process 15045 is 
legitimately busy and not hung.