Remote Serial Console HOWTO Glen Turner Australian Academic and Research Network <glen.turner+[email protected]> Mark F. Komarinski <mkomarinskiATwayga.org> v2.6 2003−03−31 Revision History Revision 2.6 2003−03−31 Revised by: gdt Correct opposing CTS/RTS explanations. Use <quote> in markup. TLDP PDF is now good, so remove instructions for rendering PostScript to PDF. Typo in GRUB configuration. Revision 2.5 2003−01−20 Revised by: gdt Only one console per technology type. Setting timezone. Use off parameter rather than comments in inittab. Cable lengths. Revision 2.4 2002−10−03 Revised by: gdt Kernel flow control bug, more cabling, Debian, Livingston Portmaster, typos (especially those found during translation to Japanese). Revision 2.3 2002−07−11 Revised by: gdt Updates for Red Hat Linux 7.3, corrections to serial port speeds and UARTs, ioctlsave. Revision 2.2 2002−05−22 Revised by: gdt Minor changes Revision 2.1 2002−05−16 Revised by: gdt Corrections to kernel console syntax. Addition of USB and devfs. Revision 2.0 2002−02−02 Revised by: gdt Second edition. Revision d1.0 2001−03−20 Revised by: mfk First edition. An RS−232 serial console allows Linux to be controlled from a terminal or modem attached to an asynchronous serial port. The monitor, mouse and keyboard are no longer required for system administration. Serial consoles are useful where Linux systems are deployed at remote sites or are deployed in high−density racks. This HOWTO describes how to configure Linux to attach a serial console. Dedication Glen Turner would like to thank his family for allowing him to work on this project for the surprisingly large number of evenings which it took to write this HOWTO. Thank you Karen, Kayla and Ella. Remote Serial Console HOWTO Table of Contents Chapter 1. Introduction......................................................................................................................................1 1.1. What is a console?............................................................................................................................1 1.2. Why use a serial console?.................................................................................................................1 1.3. Alternative meanings of "console"...................................................................................................3 1.4. Configuration overview....................................................................................................................3 Chapter 2. Preparation.......................................................................................................................................5 2.1. Create fallback position....................................................................................................................5 2.2. Select a serial port.............................................................................................................................5 2.2.1. Serial port names.....................................................................................................................5 2.2.2. Cannot share interrupt used for console's serial port...............................................................6 2.3. Select a serial speed and parameters.................................................................................................7 2.4. Configure the modem or the null−modem cable............................................................................10 2.5. Configure the terminal or the terminal emulator............................................................................10 Chapter 3. Optionally configure the BIOS.....................................................................................................11 Chapter 4. Configure the boot loader.............................................................................................................13 4.1. Configure the LILO boot loader.....................................................................................................13 4.2. Configure the GRUB boot loader...................................................................................................14 4.3. Configure the SYSLINUX boot loader...........................................................................................17 Chapter 5. Configure Linux kernel.................................................................................................................19 5.1. Configure Linux kernel using LILO...............................................................................................20 5.2. Configure Linux kernel using GRUB.............................................................................................21 5.3. Configure Linux kernel using SYSLINUX....................................................................................22 Chapter 6. Configure getty...............................................................................................................................23 6.1. init system.......................................................................................................................................23 6.2. Traditional getty..............................................................................................................................24 6.3. agetty...............................................................................................................................................25 6.4. mgetty.............................................................................................................................................26 6.5. mingetty..........................................................................................................................................27 6.6. No getty...........................................................................................................................................27 Chapter 7. Configure incidentals.....................................................................................................................29 7.1. Allow root to login from serial console..........................................................................................29 7.2. Change init level to textual.............................................................................................................29 7.2.1. Continuing to run X...............................................................................................................30 7.3. Remove saved console settings.......................................................................................................30 7.4. Serial console is not /dev/modem...................................................................................................30 7.5. Alter target of /dev/systty................................................................................................................31 7.6. Configure Pluggable Authentication Modules................................................................................32 7.7. Configure Red Hat Linux................................................................................................................33 Chapter 8. Reboot and test...............................................................................................................................35 8.1. Verify console operation.................................................................................................................35 8.2. Re−create saved console settings....................................................................................................35 i Remote Serial Console HOWTO Table of Contents Chapter 8. Reboot and test 8.3. Test the console...............................................................................................................................36 8.4. Where to next from here?...............................................................................................................37 Chapter 9. Security...........................................................................................................................................38 9.1. Use good passwords........................................................................................................................38 9.2. Obey Data Terminal Ready and Data Carrier Detect.....................................................................39 9.3. Use or configure a dumb modem....................................................................................................39 9.4. Restrict console messages...............................................................................................................40 9.4.1. Restrict console messages from the system log....................................................................40 9.4.2. Restrict broadcast messages to the console...........................................................................41 9.5. Modem features to restrict usage....................................................................................................42 9.6. BIOS features..................................................................................................................................43 9.7. Use a boot loader password............................................................................................................43 9.8. Non−interactive boot sequence.......................................................................................................43 9.9. Magic SysRq