Serial Networking Devices  «Prev  Next»

Lesson 2 Serial devices
ObjectiveDescribe serial devices supported by Red Hat Linux.

Linux Serial Devices which are supported by Red Hat

Red Hat Enterprise Linux (RHEL) 9.2 provides extensive support for a variety of serial devices. These devices communicate via serial ports, which send data one bit at a time over a communication channel or computer bus. Below is an overview of the types of serial devices supported by RHEL 9.2.
  1. Serial Ports (RS-232, RS-422, RS-485): These are standard for serial binary data interconnection between devices. They are commonly used in industrial machines, scientific instruments, and network equipment. RHEL 9.2 supports these types of serial ports and provides tools for configuring them.
  2. Universal Serial Bus (USB) Devices: USB is a modern serial communication method used to connect peripherals such as keyboards, mice, printers, and storage devices. RHEL 9.2 supports a wide range of USB devices, including USB 2.0, USB 3.x, and USB 4. USB support in RHEL includes the handling of USB serial adapters, which are often used when more serial ports are needed than the motherboard natively provides.
  3. Modems: Modems, whether internal (ISA/PCI) or external (RS-232/USB), are also supported in RHEL 9.2. This includes traditional dial-up modems as well as more modern cellular modems. For cellular modems, additional software such as ModemManager might be required to manage connections.
  4. Serial Console: A serial console is a type of physical interface through which a device can be controlled. In server environments, a serial console is often used for direct system access during boot or in case of network failure. RHEL 9.2 supports serial console operation, which can be configured through the boot loader (GRUB) and the system service getty.
  5. Bluetooth Serial Devices: RHEL 9.2 also supports Bluetooth serial devices through the rfcomm protocol. This can be used for setting up dial-up networking (DUN), serial port profile (SPP) devices, or other services that traditionally use a serial port.
  6. Serial Over LAN (SOL): RHEL 9.2 provides support for SOL, which is a mechanism that enables the input and output of the serial port of a managed system to be redirected over IP. It's usually a feature of out-of-band management solutions like Intel's Active Management Technology (AMT).
It's important to note that while RHEL 9.2 provides the drivers and tools to use these devices, additional configuration might be required depending on the specific device and its intended use. This configuration might involve setting the appropriate baud rate and parity bits for serial port communication or installing vendor-specific drivers for certain USB or Bluetooth devices. The configuration of these devices should be performed by a system administrator with a good understanding of Linux and the specific hardware being used.

Linux Serial Devices

Red Hat Linux supports common serial devices, such as:
  1. Modems
  2. Mice
  3. Serial terminals
Serial devices attach to a computer through an external interface, either a 9-pin or 25-pin RS-232 connector, known as a serial port. Alternatively, an internal device might be assigned a logical serial port, through the computer's BIOS.

RS-232 connectors
RS-232 connectors

External and internal devices, although of the same type and similar functionality, might not have the same characteristics. For example, external and internal modems both connect two computers over a phone line. External modems are completely separate devices that operate without the support of the computer's CPU. Internal modems usually cannot function as standalone devices and require the operating system to assist them. Linux supports all external modems, but only a handful of internal modems.
  1. BIOS: Basic Input and Output System. The BIOS is responsible for providing a standard interface to the computer hardware. An operating system writes to a particular BIOS specification, rather than worrying about the details for all supported hardware.
  2. The getty daemon: Actual hardwired terminals are almost never seen anymore. The idea of a connected terminal (or serial device such as a mouse) remains, however.
The getty daemon[1] and its variants support serial communications under Linux. Commonly used protocols over serial lines include PPP and SLIP. The getty daemon allows users to log in to a Linux station using a serial device, which is allocated a terminal (tty). getty assigns each user a different tty session to communicate between themselves and the machine. The next lesson explains how to administer serial ports.

[1] Daemon: A daemon is a program that waits for a request from another program. The daemon then performs the desired action, such as creating an http session, or opening and maintaining a communications socket. Some common daemons include httpd, telnetd, and ftpd.