How to list processes without using ps command?

Question

linux

At the interview, I came across the following question: Display a list of processes without using ps, pgrep, pstree, top
How can this be done?

Answer 1

find /proc -maxdepth 1 -regex ".*[0-9]"
Return pid of all processes:

/proc/1
/proc/2
/proc/39
/proc/40
/proc/41
/proc/211

Excerpt from man 5 proc

/proc/[pid]
There is a numerical subdirectory for each running process; the subdirectory is named by the process ID. Each such subdirectory contains the following pseudo-files and directories.

Answer 2

/proc

Answer 3

# pgrep ranger
5836
# head -2 /proc/5836/status
Name: ranger
State: S (sleeping)