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Ubuntu - etc - resolv.conf - Identifying which utility currently controls your /etc/resolv.conf

head /etc/resolv.conf

returns:

# This file is managed by man:systemd-resolved(8). Do not edit.
#
# This is a dynamic resolv.conf file for connecting local clients to the
# internal DNS stub resolver of systemd-resolved. This file lists all
# configured search domains.
#
# Run "systemd-resolve --status" to see details about the uplink DNS servers
# currently in use.
#
# Third party programs must not access this file directly, but only through the

NOTE: The first line here indicates that it is managed by systemd.

Some utilities don’t include a comment in the resolv.conf file, but you can identify these programs by checking for symbolic links with the following command:

ls -l /etc/resolv.conf

returns:

lrwxrwxrwx 1 root root 39 Aug  9  2019 /etc/resolv.conf -> ../run/systemd/resolve/stub-resolv.conf