The following commit:

ec8d1ad Add the package manager or any other parent process command to the commit log

breaks etckeeper on systems with Busybox ps:

ps: unrecognized option: h
BusyBox v1.29.3 (2018-11-21 11:45:56 UTC) multi-call binary.

Usage: ps [-o COL1,COL2=HEADER]

Show list of processes

       -o COL1,COL2=HEADER     Select columns for display

From the Debian manpage on the h option:

h      No header.  (or, one header per screen in the BSD personality).  The h option is problematic.  Standard BSD ps uses this
          option to print a header on each page of output, but older Linux ps uses this option to totally disable the header.  This
          version of ps follows the Linux usage of not printing the header unless the BSD personality has been selected, in which case
          it prints a header on each page of output.  Regardless of the current personality, you can use the long options --headers
          and --no-headers to enable printing headers each page or disable headers entirely, respectively.

So the use of h could affect the portability of etckeeper and the problem is not limited to Busybox ps.