For when you're on limited environment but want to see a process tree
Just use this script:
#!/bin/busybox ash
#
# Script to show process tree.
# Accepts one optional argument:
# pid of root process - by default 1 (init)
cd /tmp
# Preserve ps output to show
ps w >ps.ps
# Build list of 'parent child' pids
grep 'PPid:' /proc/*/status | sed -r 's_/proc/([^/]*)/[^0-9]*([0-9]*)_\2 \1_' >ppids.ps
# # on platforms that have more advanced `ps`
# # and lack human-readable /proc/$$/status,
# # you can use these commands, instead
# ps -e -o pid,ppid,stime,args >ps.ps
# awk '{ print $2 " " $1 }' ps.ps >ppids.ps
# own pid - we don't show own children because they're guaranteed
# to change between above two calls
self=$$
# function to show one process with all children, recursively
# args:
# * pid of process to show
# * indent - string of spaces to print before current line
showproc()
{
# print current process
echo "$2$(grep "^ *$1 " ps.ps || echo "$1 ???")"
# don't print own children
test $1 == $self && return
# print children, adding two spaces to indent
for subpid in `grep "^$1 " ppids.ps | awk '{print $2}'`; do
showproc $subpid " $2"
done
}
# start with root process (pid 1 by default)
showproc ${1:-1} ''