strace - Trace system calls and signals. A diagnostic, debugging and instructional userspace utility.
htop - htop - an interactive process viewer for Unix. This is htop, an interactive process viewer for Unix systems. It is a text-mode application (for console or X terminals) and requires ncurses. Latest release: htop 2.
ftrace - A function tracer for the Linux kernel.
Valgrind - Valgrind is an instrumentation framework for building dynamic analysis tools.
Sysdig - Sysdig is an open source, system-level exploration that capture system state and activity from a running Linux instance, then save, filter and analyze.
DTrace - DTrace is a performance analysis and troubleshooting tool for Solaris, Mac OS X and FreeBSD.