Repeating a text-output terminal command, in a scrollable ncurses-like interface?

Question

man ps says:

If you want a repetitive update of the selection and the displayed information, use top(1) instead.

... however, in some cases, I don't like the output of top - I would instead like to have the output exactly the same as ps axf:

$ ps axf
  PID TTY      STAT   TIME COMMAND
    2 ?        S      0:00 [kthreadd]
    3 ?        S      0:06  \_ [ksoftirqd/0]
    6 ?        S      0:00  \_ [migration/0]
   11 ?        S<     0:00  \_ [cpuset]
   12 ?        S<     0:00  \_ [khelper]
   13 ?        S<     0:00  \_ [netns]
   15 ?        S      0:00  \_ [sync_supers]
   16 ?        S      0:00  \_ [bdi-default]
   17 ?        S<     0:00  \_ [kintegrityd]
   18 ?        S<     0:00  \_ [kblockd]
   19 ?        S<     0:00  \_ [kacpid]
   20 ?        S<     0:00  \_ [kacpi_notify]
   21 ?        S<     0:00  \_ [kacpi_hotplug]
   22 ?        S<     0:00  \_ [ata_sff]
   23 ?        S      0:00  \_ [khubd]
   24 ?        S<     0:00  \_ [md]
   26 ?        S      0:00  \_ [khungtaskd]
   27 ?        S      0:01  \_ [kswapd0]
   28 ?        SN     0:00  \_ [ksmd]
   29 ?        S      0:00  \_ [fsnotify_mark]
   30 ?        S<     0:00  \_ [aio]
   31 ?        S      0:00  \_ [ecryptfs-kthrea]
   32 ?        S<     0:00  \_ [crypto]
   36 ?        S<     0:00  \_ [kthrotld]
   38 ?        S      0:00  \_ [scsi_eh_0]
   39 ?        S      0:00  \_ [scsi_eh_1]
   40 ?        S<     0:00  \_ [kmpathd]
...

Now, running ps axf repeatedly is not a problem (plenty of suggestions on Repeat a Unix command every x seconds forever - Unix & Linux Stack Exchange); however, as the above snippet shows, its output can be quite larger than the size of a terminal window.

So I was wondering - is there a program which can run a command repeatedly, and collect its output, and display it in something like an ncurses window? I'd ideally like to set ps axf to refresh at half a second - and I'd like to have scrolling (given that the output will overflow terminal window bounds), however, such that if the text display starts vertically from, say, line 6 on top, it stays at that position - even if the latest output of the command has more (or less) lines of text in it than the previous one.

I hoped screen may do something like this, but then, I don't think it implements any scrolling behavior... Is there a program out there that does something like this?

Answer 1

This particular point of contention has come up here on U&L a couple of times before. Mainly around the tool watch, which doesn't have this feature.

• How can I scroll within the output of my watch command?
• Is there a way to dynamically refresh the less command?
• Is there a paging version of watch?

Generally you have 3 options.

1. Use watch with this limitation
2. Use a alternative script (mywatch.sh or watchless) or tool such as pwatch
3. Use an alternative tool to ps, such as htop or atop

So I would encourage you to let go of ps and use it for what it is. A quick way to get at the state of things when in a shell. If you want to "watch" the state of the various processes running on a system use a tool such as htop. It has a "tree" view similar to the one you're asking about and you can scroll through the output.

NOTE: To toggle "treeview" simply hit the t key while in htop.

   

Kernel thread in htop?

If you'd like to see Kernel Thread in htop you can enable them. They're disabled by default. There are 2 ways to do this. You can toggle them on and off using the keyborad shortcut Shift+K.

It's also accessible from the Setup menu, F2. Once you're in the Setup menu you can use the arrow keys (←,↑,→,↓) to move around, and to mark things you use the Spacebar. Once you've picked your changes, hit Esc to get out.

   

NOTE: In the above screenshot, #1 shows you're in the Setup menu. #2 shows we've used the ↑ and ↓ arrow keys to move to Display Options. To access these options, you'd use the ← and → arrow keys to move over to the "choices" part of the menu, followed by ↑ and ↓ arrows to "select". Once you've selected an option you can use the Spacebar to toggle it.

References

• System Monitoring Software
• Why doesn't htop display the same processes as top?