In order to modify default environment PATH for ordinary users and superuser, edit file
/etc/default/login as root user, and place your additions in the line
You may have noticed that by switching user with
su command, the environment PATH variable is reset to what seems like a default value. To alter this behaviour, edit file
/etc/default/su and find the following lines:
PATH=is the value for switching toward an ordinary (non-root) user.
SUPATH=is the value for switching to the root user.