su command is used has been changed. By default execution of the su command no longer provides you with expected user environmental variables. In the case of a simple switch to administrative user
root by executing su with no arguments the expected root's PATH variable is no set properly. Symptoms
Here is an example:$ su Password: # reboot bash: reboot: command not found # adduser bash: adduser: command not found
bash: reboot: command not found - Debian GNU/Linux missing path to
/sbin/ directorySolution
The trick on how to fix this inconvenience is to explicitly tell thesu to set environment variable as if the user logs in directly. This is can be done by the use of - switch. 
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Excerpt from the
man su manual page. -, -l, --login will provide an environment similar to what the user would expect had the user logged in directly.su command with - or -l or --login swith. Example: $ su - OR $ su -l
Note the different PATH settings for both attempts to gain a root access using
su command.