System Monitoring

Linux offers many tools for monitoring your system, most of which are available through the shell. The /proc file system is used as a gateway to view kernel processes, and many applications use the information available in /proc to view the status of the kernel.

Each process is assigned a Process ID (PID) by the kernel, for example if you start Gedit, it will be assigned a PID e.g. 3924. The ps command displays a list of all the current process, their PID and some other information.

The kill command is used to stop a process. It is supplied at the command line with the PID of the process you wish to stop. There are lots of alternative options that can be used with kill - see the kill man pages.

Niceness is a measure of the priority of a process. Computer systems have finite resources and therefore some way of proiritising the processes which are all vieying for the resources - this is measured by niceness. Niceness values range from -20 (highest priority) to 19 (lowest priority). When starting a process from the command line it is possible to assign its niceness value also. the renice command is used to reassign the niceness value to a process without the need to stop the process.

The top command displays a table of all the currently running processes and several items of information about them, and the system in general. It automatically updates ever few seconds.

System memory usage can be displayed using the free command. This information is static but can be changed to dynamic by using the watch command like this

watch free

watch tells the shell to update the free command every 2 seconds

vmstat is another command that displays virtual memory statistics.

uptime displays how long the computer has been running since the last reboot and gives load averages.

A GUI for the GNOME desktop enviironment that shows all useful system information in realtime is gnome-system-monitor. It has two different types of display - list and graph. Lots of useful things can be achieved with this programme, such as changing process niceness and killing processes.