The PATH variable of the root user differs on Debian 10 when using 'su' vs 'su -', directories like /sbin are missing when only 'su' is used which means that you might get command not found errors even for basic system administration commands. So always use 'su -' on Debian 10 to become root user. The man page of 'su' also makes it clear:

2020-5-9 · Updated Debian 10: 10.4 released. May 9th, 2020. The Debian project is pleased to announce the fourth update of its stable distribution Debian 10 (codename buster).This point release mainly adds corrections for security issues, along with a few adjustments for serious problems. Debian User Forums • View topic - su: Authentication failure 2014-9-6 How to Use Sudo on Debian, CentOS, and FreeBSD - 2016-2-7 · Note: In Debian, the sudo group is often found instead of wheel. You can however manually add the wheel group using the groupadd command. For the purpose of this tutorial, we will use the sudo group for Debian. The difference between wheel and sudo. In CentOS and Debian, a user belonging to the wheel group can execute su and directly ascend to

The su command is used to switch to another user, in other words change user ID during a normal login session (that is why it is sometimes referred to as switch (-) user by a number of Linux users). If executed without a username, for example su -, it will login as root user by default.

How to Switch User Using the "su" Command 2019-11-10 · The sudo command runs any command as another user account and is commonly used to elevate permissions so that the command is run with elevated security privileges (which in Linux terms is known as the root user).Sudo works for a brief period of time. To run as another user for a prolonged period of time then use the su command.

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su allows to run commands with a substitute user and group ID. When called without arguments, su defaults to running an interactive shell as root . For backward compatibility, su defaults to not change the current directory and to only set the environment variables HOME and SHELL (plus USER and LOGNAME if the target user is not root).