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How can I get the entire process tree spawned by a given process displayed as a tree and only that tree i.e. no other processes?

The output could e.g. look like

 4378 ?        Ss     0:10 SCREEN
 4897 pts/16   Ss     0:00  \_ -/bin/bash
25667 pts/16   S+     0:00  |   \_ git diff
25669 pts/16   S+     0:00  |       \_ less -FRSX
11118 pts/32   Ss+    0:00  \_ -/bin/bash
11123 pts/32   S+     0:00      \_ vi

I couldn't get the desired result purely with parameters to ps.

The following gives the desired result but seems a bit involved:

#!/bin/bash

pidtree() {
  echo -n $1 " "
  for _child in $(ps -o pid --no-headers --ppid $1); do
    echo -n $_child `pidtree $_child` " "
  done
}

ps f `pidtree 4378`

Does anyone have an easier solution?

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Not an answer, but start with ps auxf. –  jftuga Nov 30 '11 at 21:34
2  
@jtfuga This is in fact where I started, but this gives me all processes, which is exactly what I don't want. –  kynan Dec 1 '11 at 9:59

5 Answers 5

pstree ${pid}

where ${pid} is the pid of the parent process.

On gentoo pstree is in the package "psmisc," apparently located at http://psmisc.sourceforge.net/

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4  
Thanks, should have mentioned that I had looked at pstree, but missed a more verbose output format. However, pstree -p <pid> at least print the pids which is reasonably close. –  kynan Dec 1 '11 at 10:00
1  
I have this problem too, I need to gather all child pids recursively but I need only the pids, so I would have to sed all that.. mmm this works :) pstree -pn 4008 |grep -o "([[:digit:]]*)" |grep -o "[[:digit:]]*" –  Aquarius Power Jun 17 at 23:36

Here is my version that runs instantly (because ps executed only once). Works in bash and zsh.

pidtree() (
    [ -n "$ZSH_VERSION"  ] && setopt shwordsplit
    declare -A CHILDS
    while read P PP;do
        CHILDS[$PP]+=" $P"
    done < <(ps -e -o pid= -o ppid=)

    walk() {
        echo $1
        for i in ${CHILDS[$1]};do
            walk $i
        done
    }

    for i in "$@";do
        walk $i
    done
)
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The pstree is a very good solution, but it is a little bit reticent. I use ps --forest instead. But not for a PID (-p) because it prints only the specific process, but for the session (-g). It can print out any information ps can print in a fancy ASCII art tree defining the -o option.

So my suggestion for this problem:

ps --forest -o pid,tty,stat,time,cmd -g 2795

If the process is not a session leader, then a little bit more trick has to be applied:

ps --forest -o pid,tty,stat,time,cmd -g $(ps -o sid= -p 2795)

This gets the session id (SID) of the current process first and then call ps again with that sid.

If the column headers are not needed add a '=' after each column definition in '-o' options, like:

ps --forest -o pid=,tty=,stat=,time=,cmd= -g $(ps -o sid= -p 2795)

An example run and the result:

$ ps --forest -o pid=,tty=,stat=,time=,cmd= -g $(ps -o sid= -p 30085)
27950 pts/36   Ss   00:00:00 -bash
30085 pts/36   S+   00:00:00  \_ /bin/bash ./loop.sh
31888 pts/36   S+   00:00:00      \_ sleep 5

Unfortunately this does not work for screen as it sets the sid for each child screen and all grandchild bash.

To get all the processes spawned by a process the whole tree needs to be built. I used for that. At first it builds a hash array to contain all PID => ,child,child... . At the end it calls a recursive function to extract all the child processes of a given process. The result is passed to another ps to format the result. The actual PID has to be written as an argument to instead of <PID>:

ps --forest $(ps -e --no-header -o pid,ppid|awk -vp=<PID> 'function r(s){print s;s=a[s];while(s){sub(",","",s);t=s;sub(",.*","",t);sub("[0-9]+","",s);r(t)}}{a[$2]=a[$2]","$1}END{r(p)}')

For a SCREEN process (pid=8041) the example output looks like this:

  PID TTY      STAT   TIME COMMAND
 8041 ?        Ss     0:00 SCREEN
 8042 pts/8    Ss     0:00  \_ /bin/bash
 8092 pts/8    T      0:00      \_ vim test_arg test_server
12473 pts/8    T      0:00      \_ vim
12972 pts/8    T      0:00      \_ vim
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I have been working to find a solution to the exact same problem. Bascially, ps manpage does document any option allowing to do what we want with a single command. Conclusion: a script is needed.

I came up with a script very similar to yours. I pasted it in my ~/.bashrc so I can use it from any shell.

pidtree() {
  local parent=$1
  local list=
  while [ "$parent" ] ; do     
    if [ -n "$list" ] ; then
      list="$list,$parent"
    else
      list="$parent"
    fi
    parent=$(ps --ppid $parent -o pid h)
  done
  ps -f -p $list f
}
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I made a similar script based on Philippe's above

pidlist() {
local thispid=$1
local fulllist=
local childlist=
childlist=$(ps --ppid $thispid -o pid h)
for pid in $childlist
do
  fulllist="$(pidlist $pid) $fulllist"
done
echo "$thispid $fulllist"
}

This outputs all the child, grandchild, etc. pids in space-delimited format. This can, in turn, be fed to ps, as in

ps -p $(pidlist pid)

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