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Florida State College at Jacksonville *

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4640

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Information Systems

Date

Oct 30, 2023

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docx

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About the unix boost processes - Booting (bootstrapping) is the process of getting a computer system ready. o Can be done automatically or manually o Cold boot: initiated when the computer is on o Warm boot/restart: reboot command from a running system From Power On to Loading the Kernel - Firmware (BIOS, ROM, NVRAM) stores the initial boot instructions, which is executed when starting the boot process - Boot instructions may also execute in response to a command o They are used to locate and start up the system’s boot program – Unix OS o The boot program loads the Unix kernel into memory and passes control of the system to it. - A system usually has multiple bootable devices. o Without instructions, the system uses the first bootable device that is found. - Kernel is the part of the Unix OS that runs at all times when the system is up. o It is traditionally stored in or linked to the root directory o Typical Kernel names and directory locations: o The kernel, when given control, runs its preparation and creates another process that will run the “init” program as the process with PID1 (process identifier 1) Booting to Multiuser Mode - Init is the ancestor of all subsequent Unix processes and the direct parent of user login shells. - Init activities: o (IMPORTANT) Verify the integrity of the local filesystems, beginning with the root filesystem. o Checking the integrity of the filesystems (using “fsck”) o Mounting local disks o Designating and initializing paging areas o Performing filesystem cleanup activities o Starting system server processes (daemons) for subsystems like printing, email, accounting, error logging, and “cron” o Starting networking daemons and mounting remote disks o Enabling user logins (starting “getty” processes and/or the graphical login interface on the system console and removing the file /etc/nologin, if present - These activities are carried out by means of system initialization scripts, which are shell scripts executed by init at boot time. - Once the activities are complete, so is the process and the system is said to be in multiuser mode.

Booting to Single-User Mode - The init program can place the system in single-user mode by not completing the initialization tasks required for multiuser mode. - Single-user mode (maintenance mode) is designed for admin and maintenance activities, requiring complete and unshared system control. - System might enter single-user mode automatically if it can’t handle problems in boot process o Instead of picking up the boot process where it left off, the system may be rebooted by command “reboot” or “telinit 6” - Single-user mode = minimal system startup. The search path + terminal type are often set incorrectly (no running daemons + many shutdown Unix facilities) + no network connection + files are mounted read-only. - Password protection for single-user mode o Most systems now require that the root password be entered before granting system access. o On some System V-based systems, this is done via “sulogin” program that is invoked automatically by “init” once the system reaches single user mode. o Summary of single-user mode password protection: - Firmware Passwords o Some systems also allow you to assign a separate password to the firmware initialization program. o On some systems, you must use commands within the firmware program itself to perform this operation o On Linux systems, commonly used boot-loader programs have configuration settings to do the above Starting a Manual Boot - If autobooting is not enabled when the computer is powered on, it can be done via commands. - Low-level boot commands for: - AIX:

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