uptime gives a one line display of the following information. The current time, how long the system has been running, how many users are currently logged on, and the system load averages for the past 1, 5, and 15 minutes.

pavs

This is a system call, and the operating system presumably knows its name, release and version. It also knows what hardware it runs on. So, four of the fields of the struct are meaningful. On the other hand, the field nodename is meaningless: it gives the name of the present machine in some undefined network, [...]

ps displays information about a selection of the active processes. If you want a repetitive update of the selection and the displayed information, use top(1) instead.
This version of ps accepts several kinds of options:
1 UNIX options, which may be grouped and must be preceded by a dash.
2 BSD options, which may be grouped and must [...]

The iostat command is used for monitoring system input/output device loading by observing the time the devices are active in relation to their average transfer rates. The iostat command generates reports that can be used to change system configuration to better balance the input/output load between physical disks.
The first report generated by the iostat command [...]