How to find ancestor chain of a process?

I can do ps -o "pid,ppid,args" -p my_pid to find the parent of my_pid.

I can continue ps -o "pid,ppid,args" -p previously_found_ppid in a loop until get to ppid=1.

However, I bet, there is a single call solution that would start with my_pid and list all its ancestors. Something reverse to pstree that starts with the parent and list all its descendants. Could you tell whether such Unix/Linux command is readily available?

It looks like pstree can do what you want, with it's -s Show parent processes of the specified process option

$ pstree -s 5698 
init───mdm───mdm───init───at-spi-bus-laun───dbus-daemon

Or more info (arguments) and prettier with the -a option

mint@mint ~ $ pstree -s -a 5698 
init
  └─mdm
      └─mdm
          └─init --user
              └─at-spi-bus-laun
                  └─dbus-daemon --config-file=/etc/at-spi2/accessibility.conf ...

Or a few options together

$ pstree -s -p -a -G -l 5698 
init,1
  └─mdm,1994
      └─mdm,5358
          └─init,5379 --user
              └─at-spi-bus-laun,5691
                  └─dbus-daemon,5698 --config-file=/etc/at-spi2/accessibility.conf --nofork --print-address 3

pstree can be used to print all the ancestors of a process. But latest Linux distributions uses systemd instead of init.

Example: pstree -p -s 6206 will give following output

systemd(1)───lightdm(1066)───lightdm(1191)───upstart(1360)───gnome-terminal-(5222)───bash(5229)───cpu-print(6206)

A systemd, may refer to all the packages, utilities and libraries around daemon. It was designed to overcome the shortcomings of init [1].

reference [1]:https://www.tecmint.com/systemd-replaces-init-in-linux/

How to find ancestor chain of a process?

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