How to get child process from parent process

Question

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

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I am not sure if I understand you correctly  does this help   ps --ppid  lt pid of the parent gt

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To get the child process and thread  pstree -p PID  It also show the hierarchical tree

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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  quot cpids  cpids quot      for cpid in  cpids      do         echo  quot  cpid quot          getcpid  cpid     done    getcpid  1

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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   quot   children     stat pid    24243    pid quot  24243 24259 24284 24289 24260 24262 24333 24337 24439 24570 24592 24606

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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

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include lt stdio h gt   include  lt sys types h gt   include  lt unistd h gt   int main            Create a child process          int pid   fork         if  pid  gt  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

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Just use    pgrep -P  your process1 pid

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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

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You can get the pids of all child processes of a given parent process  lt pid gt  by reading the  proc  lt pid gt  task  lt tid gt  children entry  This file contain the pids of first level child processes  For more information head over to https   lwn net Articles 475688

[linux] How to get child process from parent process

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