UNIX Startup and Shutdown CSCI N321 – System and Network Administration Copyright © 2000, 2012 by Scott Orr and the Trustees of Indiana University

Section Overview Bootstrapping Startup Scripts and Run Levels Boot Configuration and Troubleshooting System Shutdown

References CQU COIT13146 System Administration Course Chapter 13

Monolithic Kernels Hardware Device Drivers, Dispatcher, … Scheduler, Virtual Memory IPC, File System VFS Application Source: KernelMode UserMode

Microkernels Hardware Basic IPC, Virtual Memory, Scheduling ApplicationIPC Source: KernelMode UserMode UNIXServer DeviceDriversFileServer Application

Bootstrapping Starting the system Process of loading kernel into memory Boot Modes Normal Single User/Safe Mode Rescue (on DVD)

RedHat Boot Process BIOS LoginShell GRUB /etc/inittab Source: LinuxKernelinit /etc/rc.d/rc.sysinit/etc/rc.d/rc RL Specific /etc/inittab/etc/rc.d/rc3.d/etc/rc.d/rc5.d

Fedora Boot Process BIOS LoginShell GRUB Source: LinuxKernelinit Systemd/etc/init/*.conf RL Specific /etc/rc.d/rc3.d/etc/rc.d/rc5.d systemd

Boot Process Power On Self Tests (POST) Run Boot Loader(s) Load & initialize kernel Detect & configure devices Fork system processes (Stop if Single User mode) Run startup scripts Start multiuser operations

Boot Loader ROM loads Master Boot program from disk Primary Bootloader BIOS - Basic I/O, Program Loading UEFI – Unified Extensible Firmware Interface 2 nd Boot Loader finds/loads kernel Checks available memory Initializes kernel internal data structures NTLDR – Microsoft Boot Loader GRand Unified Bootloader (GRUB/GRUB2) Can boot multiple OS Boot options can be edited at boot

GRUB Images (/boot/grub2) boot.img – Loaded first on BIOS systems diskboot.img – first sector of core image cdboot.img – DVD version of diskboot.img core.img Main image Includes kernel.img and module lists Built with grub-mkimage kernel.img – Basic run-time functions *.mod – Dynamically loadable modules

Basic grub.cfg options Shell script in /etc/boot2 set default=“0” set timeout=“5” menuentry ‘Fedora’ set root=‘(hd0,gpt2)’ linux /vmlinuz- initrd /initranfs-

Creating grub.cfg Compiled using grub2-mkconfig /etc/default/grub Variables to change default settings /etc/grub.d/* 00_header 10_linux 40_custom

System Processes BSD Systems swapper – PID 0 init – PID 1 pagedaemon – PID 2 AT&T SVR4 sched – PID 0 (invisible under RedHat) init – PID 1 /etc/inittab

Startup Services Hostname Timezone Check the hard drives Mount the hard drives Remove files from /tmp Configure network interfaces Start daemons and network services

BSD /etc/rc* Scripts /etc/rc Master script Executes supplemental scripts Example supplemental scripts (freeBSD) /etc/defaults/rc.conf /etc/rc.conf /etc/rc.conf.local

/etc/inittab Initializes system for use Format: id:rl:action:process id : uniquely identifies entry rl : Run level entry applies to action : How to execute process process : process command line Ex: Setting the default Runlevel: id:3:initdefault Replaced in Fedora with systemd

Systemd Becoming more prevalent in Linux Distros Currently used by Fedora and OpenSUSE Testing in Debian Mostly compatible with the init system init scripts are read as alternative format Established functionality such as fstab still supported

Systemd - Units Uses a dependency system between “units” Requires/Wants Conflicts Before After Encapsulate objects relevant to booting and maintenance Configured in config files May be tied through symbolic links

Systemd – Unit Types Different unit types control different aspects of the operating system service: handles daemons socket: handles network sockets target: Logical grouping of units (example: runlevel) device: expose kernel devices mount: controls mount points of the files system automount: mounts the file system snapshot: references other units (similar to targets)

Systemd Unit File Section [Unit] Description Requires Wants Conflicts Before After

Systemd Service Section [Service] Type= simple|oneshot|forking|dbus|notify|idle ExecStart ExecReload ExecStop Restart= no|on-success|on-failure|on-abort|always

Systemd Install Section [Install] Wantedby= Used to determine when to start (e.g. Runlevel)

Startup Run Levels RedHatMode 1 (S)Single user 2Multiuser (no networking) 3Full Multiuser 4Unused 5X11 6Reboot 0Halt

Systemd – Runlevels Runlevel is defined through a symbolic to one of the runlevel targets Runlevel Target Runlevel 3: /lib/systemd/system/multi-user.target Runlevel 5: /lib/systemd/system/graphical.target Change Runlevel: Remove current link /etc/systemd/system/default.target Add a new link to the desired runlevel

Systemd - Virtual Consoles Started in /etc/systemd/system/getty.target /sbin/agetty agetty Alternative Linux getty Opens tty port and prompts for login

Systemd - Virtual Consoles Example: [Unit] Description=Getty on %I BindTo=dev-%i.device … [Service] Environment=TERM=linux ExecStart=-/sbin/agetty %I Restart=always RestartSec=0 UtmpIdentifier=%I KillMode=process …

/etc/init/*.conf directives exec script start on stop on task respawn See man 5 init for more

“Events” control-alt-delete power-status-changed startup runlevel started stopped

/etc/init - Virtual Consoles Started in /etc/init/start-ttys.conf tty restarts in /etc/init/tty.conf Example: /etc/init.d/tty.conf: # tty - getty # # This service maintains a getty on the sepcified device. stop on runlevel [016] respawn instance $TTY exec /sbin/mingetty $TTY

Started in /etc/init/rc[S].conf : Example (rc.conf): start on runlevel [ ] stop on runlevel [!$RUNLEVEL] task export RUNLEVEL console output exec /etc/rc.d/rc $RUNLEVEL /etc/init - Run Levels

Run Level Scripts Actual scripts - /etc/rc.d/init.d/ /etc/rc.d/rc#.d/ Symbolic links to /etc/init.d scripts S## - Start scripts K## - Stop scripts /etc/sysconfig/ - script configuration files chkconfig on|off service start|stop|restart

Startup Messages Displayed to console RedHat – daemon [ ok ] /bin/dmesg History of boot messages Convenient to search RedHat allows for interactive setup (“i”)

Windows Boot Options When system starts booting…

Boot Display During Safe Mode

System Shutdown Turn off power – BAD!!! Reboot reboot shutdown –r Halting the system halt shutdown –h Changing the Run Level telinit shutdown –i

When to Shutdown Failures Maintenance and Upgrades Regularly Scheduled Housecleaning Window for Maintenance/Upgrades User Notification /etc/motd Support web pages