A Linux administrator has downloaded and installed the httpd package. Which of the following commands will start the service immediately and allow the service to start on system boot?

The command `systemctl start httpd` immediately starts the `httpd` service. The command `chkconfig httpd on` configures the service to start automatically during the boot process across different runlevels, though `systemctl enable httpd` is the more modern and preferred method for persistent enablement.

`systemctl status httpd` only shows the current status of the service; it does not start it.

`systemctl.start` is a syntax error; the correct command is `systemctl start`.

Adding `6` to `chkconfig httpd on` is incorrect syntax; `chkconfig` manages runlevels implicitly or with specific options, not as a bare number at the end of `on`.