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I am trying to have a terminal showing the last 5 processes opened. This is helpful for my debugging.

At this point I have

watch ps -ef --sort=start_time

This works fine but it shows all processes so they don't fit in the screen. How can I limit it to a specific number like 5 or 10?

-- Update --

A have tried

watch "ps -ef --sort=start_time | tail -n 5"

but the problem is that the header of ps is omitted so after a while I don't know what I am looking at.

  • watch ps -ef --sort=start_time | head -5 or watch ps -ef --sort=start_time | tail -5 depending on whether the sort is ascending or not – mnmnc Jul 23 '14 at 9:45
2

You want:

watch "ps -ef --sort=start_time | tail -n 5"

tail will only output the last n lines piped to it.

I assume you tried:

watch ps -ef --sort=start_time | tail -n 5

Which would try and pipe the output of watch to tail, rather than the output of ps, and as watch never terminates, tail can't determine when the last n lines are output, so also prints nothing.


If you wish to keep the header as well, you can use some clever bash to simply:

watch "ps -ef --sort=start_time | (head -n 1 ; tail -n 5)"

Which causes head to print the top line as well.

  • I tried this. The problem is that the header line is then omitted. Would prefer if I could keep the header.. – Pithikos Jul 23 '14 at 9:51
  • Apologies, I fell into the exact pitfall I mentioned in the middle of my post, try now! – Andrew Stubbs Jul 23 '14 at 10:01
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    The combination of head and tail on a single pipe does not work reliably, but only if the ps output is longer than head's input buffer (try watch "ps -f --sort=start_time | (head -n 1 ; tail -n 5)" to see what I mean). To make sure that both programs see all the output, you need to use a temporary file, eg watch "ps -ef --sort=start_time >TempFile; head -n 1 <TempFile ; tail -n 5 <TempFile" (you could also use tee to create tempFile). Both -f and -ef now show the last five lines. – AFH Jul 23 '14 at 11:55

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