Is it possible to get the child process id from parent process id in shell script?
I have a file to execute using shell script, which leads to a new process process1 (parent process). This process1 has forked another process process2(child process). Using script, I'm able to get the pid of process1 using the command:
cat /path/of/file/to/be/executed
but i'm unable to fetch the pid of the child process.
This question is related to
linux
shell
process
child-process
To get the child process and thread,
pstree -p PID
.
It also show the hierarchical tree
For the case when the process tree of interest has more than 2 levels (e.g. Chromium spawns 4-level deep process tree), pgrep
isn't of much use. As others have mentioned above, procfs files contain all the information about processes and one just needs to read them. I built a CLI tool called Procpath which does exactly this. It reads all /proc/N/stat
files, represents the contents as a JSON tree and expose it to JSONPath queries.
To get all descendant process' comma-separated PIDs of a non-root process (for the root it's ..stat.pid
) it's:
$ procpath query -d, "..children[?(@.stat.pid == 24243)]..pid"
24243,24259,24284,24289,24260,24262,24333,24337,24439,24570,24592,24606,...
I am not sure if I understand you correctly, does this help?
ps --ppid <pid of the parent>
You can get the pids
of all child processes of a given parent process <pid>
by reading the /proc/<pid>/task/<tid>/children
entry.
This file contain the pids of first level child processes.
For more information head over to https://lwn.net/Articles/475688/
ps -axf | grep parent_pid
Above command prints respective processes generated from parent_pid
, hope it helps.
+++++++++++++++++++++++++++++++++++++++++++
root@root:~/chk_prgrm/lp#
parent...18685
child... 18686
root@root:~/chk_prgrm/lp# ps axf | grep frk
18685 pts/45 R 0:11 | \_ ./frk
18686 pts/45 R 0:11 | | \_ ./frk
18688 pts/45 S+ 0:00 | \_ grep frk
The shell process is $$
since it is a special parameter
On Linux, the proc(5) filesystem gives a lot of information about processes. Perhaps
pgrep(1) (which accesses /proc
) might help too.
So try cat /proc/$$/status
to get the status of the shell process.
Hence, its parent process id could be retrieved with e.g.
parpid=$(awk '/PPid:/{print $2}' /proc/$$/status)
Then use $parpid
in your script to refer to the parent process pid (the parent of the shell).
But I don't think you need it!
Read some Bash Guide (or with caution advanced bash scripting guide, which has mistakes) and advanced linux programming.
Notice that some server daemon processes (wich usually need to be unique) are explicitly writing their pid into /var/run
, e.g. the sshd
server daemon is writing its pid into the textual file /var/run/sshd.pid
). You may want to add such a feature into your own server-like programs (coded in C, C++, Ocaml, Go, Rust or some other compiled language).
I've written a script to get all child process pids of a parent process. Here is the code. Hope it will help.
function getcpid() {
cpids=`pgrep -P $1|xargs`
# echo "cpids=$cpids"
for cpid in $cpids;
do
echo "$cpid"
getcpid $cpid
done
}
getcpid $1
#include<stdio.h>
#include <sys/types.h>
#include <unistd.h>
int main()
{
// Create a child process
int pid = fork();
if (pid > 0)
{
int j=getpid();
printf("in parent process %d\n",j);
}
// Note that pid is 0 in child process
// and negative if fork() fails
else if (pid == 0)
{
int i=getppid();
printf("Before sleep %d\n",i);
sleep(5);
int k=getppid();
printf("in child process %d\n",k);
}
return 0;
}
Source: Stackoverflow.com