Score:4

Ubuntu

pstree does not show every process

new_x

7/8/24, 5:35 PM

I opened a terminal made sudo su run the nano editor in the background by running it as nano&.

I tried to find the newly started nano process in the process list.
To do that, I typed

ps aux|grep -i nano

-> Saw the newly created nano

but when I tried to see the same nano process with pstree, it did not list the nano. I used

pstree -p|grep -i nano

No output was shown.

367

2 + 1

process

Raffa

7/8/24, 5:47 PM

`pstree -ap | grep -i nano` ... with `-a` should show it.

Score:6

Ubuntu

steeldriver

7/8/24, 6:22 PM

It appears that pstree truncates long lines when piped e.g.

# pstree -sp "$$"
systemd(1)───sddm(1007)───sddm-helper(1097)───lxqt-session(1114)───qterminal(1475)───bash(1478)───sudo(28929)───sudo(28930)───su(28931)───bash(28932)─┬─nano(28938)                          
                                                                                                                                                      └─pstree(29086)

but

# pstree -sp "$$" | cat                                                                                                                   
systemd(1)---sddm(1007)---sddm-helper(1097)---lxqt-session(1114)---qterminal(1475)---bash(1478)---sudo(28929)---sudo(28930)---su(28+

(notice everything after sudo(28930)---su(28+ is omitted).

You can pass the -l or --long option to prevent that, i.e.

# pstree -lsp "$$" | grep -i nano                                                                                                           
                                                                                                                                                      |-nano(28938)

or avoid the issue by not starting all the way from PID 1 - for example, starting from the parent shell's PID:

# pstree -p "$$" | grep -i nano
            |-nano(28938)

or (perhaps better) avoid grepping the pstree output (which is really intended for human eyes) by using pgrep instead:

# pgrep -af nano
28938 nano

+ 4

Raffa

7/8/24, 6:26 PM

What a coincidence :) +1

steeldriver

7/8/24, 6:29 PM

@Raffa indeed ;-p

new_x

7/8/24, 7:32 PM

Thank both of you. Since Rafta is the first I chose his answer. But thank you steeldriver for your super explanation

David Z

7/9/24, 2:09 AM

+1 for the suggestion of `pgrep`

Score:3

Ubuntu

Raffa

7/8/24, 6:25 PM

pstree through a pipe .. Check it with:

pstree -p | tee

might not show the full command/command-line arguments depending on how far to the right side of the tree a process is ... It might show a partial command followed by a plus sign indicating the output is shortened like --nan+ instead of --nano or might not even show that if that process is far enough to the right side of the processes tree.

Therefore, if you need to show command line arguments, then use the option for that which is -a:

pstree -ap | grep -i nano

Although grep is more suitable to ps than it is to pstree as the "tree" part will be lost ... If you have to use pstree with grep then at least use grep's -B and -A options to show a few lines before and after the match so that the "tree" is at least partially shown like so:

pstree -ap | grep -B 5 -A 5 -i nano

+ 2

Unmitigated

7/10/24, 2:08 AM

`-B 5 -A 5` can be replaced with `-C 5`.

Raffa

7/10/24, 7:41 AM

@Unmitigated Thanks for your comment ... That is correct as well as alternatively using only a dash `-` and a number i.e. `-5` at least on Ubuntu's implementation of GNU grep, but `-B` and `-A` offer more control of course.

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EN: pstree does not show every process

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