Monitor processes

A brief introduction to monitoring processes on the CCB cluster.

Snapshot current processes #

The ps command can be used to report a snapshot of the current processes.

ps

The output of the ps command will always include at least two entries:

• The bash process that is used to run the current Bash session.
• The ps process itself, which is being being executed to snapshot currently running processes.

Then, any other process that is currently running will be reported by the ps command.

For instance:

sleep 10 &
sleep 20 &
sleep 30 &
ps

In particular:

• PID – Process identifier (unique).
• TTY – Terminal type.
• TIME – CPU runtime.
• CMD – Process name.

Real-time monitoring #

The commands top and htop can be used to display a dynamic real-time view of a running system.

top #

The top command can be used to monitor processes and resource usage in real time.

Information is displayed as a table that can be filtered and sorted.

Above the table, a header displays system-wide information (e.g., total number of processes, memory available).

top

htop #

The htop command can be used to launch an interactive process viewer.

Similarly to the top command, informatio is displayed as a table that can be filtered and sorted, as well as a header that displays system-wide information (e.g., total number of processes, memory available, CPU usage).

htop

An annotated example output of the htop command is presented below.

Terminate a process #

kill #

Processed can be terminated (often said ‘killed’), either by users – including system administrators – or by the system itself.

Common reasons for terminating processes include:

• They are taking too long (e.g., froze, entered an infinite loop).
• They are using too many resources (e.g., memory, open file connections).
• They are no longer functioning properly.

The kill command can be used to terminate processes specified by their PID (Process IDentifier).

sleep 30 &
ps
kill <PID>

killall #

The killall command can be used to terminate all processes by name.

For instance, the code below launches a series of sleep commands, and then terminates all of them by name, without the need to specify their respective PID.

sleep 30 &
sleep 40 &
sleep 50 &
ps
killall sleep

Cheatsheet #

Common options for the ps command are listed below:

For instance, replace <user> by your own username and run the command below to display only your processes in full format:

ps -f -u <username>