Strace is a Linux command that allows you to follow what a process on your server is doing. Let's say process 351711 has been running for an extended period, and you're wondering if it's doing anything, or it's hung/stuck - strace is perfect for such situations! First of all, we need to install it.
yum install strace
Debian and Ubuntu:
apt-get install strace
Once it's installed, it's as simple as running strace -p PID (where PID is the process ID).
If there's no process running, you'll see something like this:
# strace -p 351711
strace: attach: ptrace(PTRACE_ATTACH, ...): No such process