The `su` command allows one user to temporarily assume the identity of another user. By default, `su` assumes the identity of the superuser, but a different user can be specified. When using `su`, the user’s password is required unless the command is run by the superuser. The default shell for the user is used, or `/bin/sh` if none is specified. The current directory is not changed by default. Various options can be used with `su`, including `-c` to run a specific command and `-l` to make the shell a login shell. GNU su does not support the `wheel` group.
https://ftp.gnu.org/old-gnu/Manuals/coreutils-4.5.4/html_node/coreutils_149.html