ps: How can i recursively get all child process for a given pid
Solution 1:
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 awk 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 awk 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
Solution 2:
pstree ${pid}
where ${pid}
is the pid of the parent process.
On Gentoo Linux, pstree
is in the package "psmisc," apparently located at http://psmisc.sourceforge.net/
Solution 3:
Here is my version that runs instantly (because ps
executed only once). Works in bash and zsh.
pidtree() (
[ -n "$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
)
Solution 4:
I've created a small bash script to create a list pid's of a parent's child process(es). Recursively till it finds the last child process which does not have any childs. It does not give you a tree view. It just lists all pid's.
function list_offspring {
tp=`pgrep -P $1` #get childs pids of parent pid
for i in $tp; do #loop through childs
if [ -z $i ]; then #check if empty list
exit #if empty: exit
else #else
echo -n "$i " #print childs pid
list_offspring $i #call list_offspring again with child pid as the parent
fi;
done
}
list_offspring $1
first argument of list_offspring is the parent pid
Solution 5:
ps -H -g "$pid" -o comm
doesn't add a tree per se, it is just the list of processes.
gives for example
COMMAND
bash
nvim
python