After all the upgrade hype, Now we will start getting a flood of questions about Why this or that command does not work ? Simply because so many Debian users do not read any documentation, and have no clue that they need to be using :
when they wannbee root,
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Probably a waste of time, since no one reads any thing any more, but for those that do:
https://wiki.debian.org/NewInBuster
Changes
The su command in buster is provided by the util-linux source package, instead of the shadow source package, and no longer alters the PATH variable by default. This means that after doing su, your PATH may not contain directories like /sbin, and many system administration commands will fail. There are several workarounds:
Use su - instead; this launches a login shell, which forces PATH to be changed, but also changes everything else including the working directory.
Use sudo instead. sudo still runs commands with an altered PATH variable.
To get a regular root shell with the correct PATH, you may use sudo -s.
To get a login shell as root (equivalent to su -), you may use sudo -i.
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There is much more, and honestly, Please read it