Linux proc question!

Let me answer you by assuming that your environment is Linux.

ls/proc 1, 41, 57 etc. pid.

ps-ef You can see that the pid of mysql is 1.

cat /proc/1 where number 1 is mysql's pid. The command you ran mysqld appears.

You can get more information by searching for proc or cmdline.

http://man7.org/linux/man-pages/man5/proc.5.html