htop is an interactive process viewer for Linux, replacing the traditional top.
htop provides a more interactive process-viewing experience. You can surf through running processes, scrolling horizontally and vertically to reveal information that would otherwise have been clipped, information such as full command lines.
You can see what files a process has open (click "l"); you can even trace processes using strace. There's also a handy tree view for understanding process ancestry.
Installing on Linux
yum install htop
sudo apt-get install htop
Installing on FreeBSD
Add the following line to /etc/fstab:
linproc /compat/linux/proc linprocfs rw 0 0
Create a symbolic link for /usr/compat
mkdir -p /usr/compat/linux/proc ; ln -s /usr/compat /compat ; mount linproc
Compile and install