I have being playing today with perf on latest available kernel in Fedora (3.13). These are just some observations and thoughts. perf trace This tool is similar to strace, but almost without overhead. Contrary to strace, you can use perf trace to watch syscalls system wide or system calls generated by processes owned by certain user. perf top Function names are shown correctly and -g parameter is now available. It means that you can get call traces in a real time (without perf record). Read more

Sometimes you will see processes on your linux box that are in D state as shown by ps, top, htop or similar. D means uninterruptible sleep. As opposed to normal sleep, you can’t do anything with these processes (i.e. kill them). Additional information could be found on LWN. Usually this means that process is stuck reading or writing something to disk or NFS and remote site does not answer. But not always. Read more