While running
gksu gedit /etc/udev/rules.d/somefile.rules
I am getting this suggestion.
Command 'gksu' not found, did you mean:
command 'gosu' from deb gosu
command 'ksu' from deb heimdal-clients
command 'ksu' from deb krb5-user
Try: sudo apt install <deb name>
gksu has been deprecated.
It's been removed from Ubuntu 18.04, as well as Debian and other newer Linux distributions. If you do a web search with the phrase "Ubuntu man gksu", you will see there's no 18.04 version available. Here are alternatives:
Alternate[0]: use "-H"
Alternate[1]: Use "admin://"
Alternate[2]: Use "pkexec"