Change the effective user id and group id to that of USER. A mere - implies -l. If USER not given, assume root.
Options: -m, -p, --preserve-environment do not reset environment variables -g, --group <group> specify the primary group -G, --supp-group <group> specify a supplemental group
-, -l, --login make the shell a login shell -c, --command <command> pass a single command to the shell with -c --session-command <command> pass a single command to the shell with -c and do not create a new session -f, --fast pass -f to the shell (for csh or tcsh) -s, --shell <shell> run shell if /etc/shells allows it
-h, --help display this help and exit -V, --version output version information and exit