Init is the parent of all processes


unisys18:~$ pstree


init-+-atd
     |-cron
     |-dhclient3
     |-5*[getty]
     |-inetd
     |-klogd
     |-login---bash---pstree 
     |-portmap
     |-rpc.statd
     |-sshd
     |-syslogd
     `-udevd


unisys18:~$ pstree -p -l

shows the process tree with their PID in the long (non-truncated) format. /usr/bin/pstree comes with package psmisc.

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