How to get parent PID of a given process in GNU/Linux from command line?

Question

Resolved before asked: cat /proc/1111/status | grep PPid

Answer 1

Command line:

ps -p 1111 -o ppid=

Function:

ppid () { ps -p ${1:-$$} -o ppid=; }

Script:

#!/bin/sh
pid=$1
if [ -z $pid ]
then
    read -p "PID: " pid
fi
ps -p ${pid:-$$} -o ppid=

If no PID is supplied to the function or the script, they default to show the PPID of the current process.

Answer 2

Parent pid is in shell variable PPID, so

echo $PPID

Answer 3

This is one of those things I learn, forget, relearn, repeat. But it's useful. The pstree command's ‘s’ flag shows a tree with a leaf at N:

pstree -sA $(pgrep badblocks)
systemd---sudo---mkfs.ext4---badblocks

Answer 4

Read /proc/$PID/status. Can be easily scripted:

#!/bin/sh
P=$1
if [ -z "$P" ]; then
    read P
fi
cat /proc/"$P"/status | grep PPid: | grep -o "[0-9]*"

Answer 5

Run top with whatever options you want, like -u username and -p PID.

And while top is working press F, it shows a list of options you want to display in top output, and the displayed parameters will be shown in CAPITAL letters and the parameters which or not displaying will be shown in small letters.

So by entering the letter before the parameter you can enable or disable it. For parent process ID you have to enter B and then press Enter, it'll display the PPID in top output.