Bài giảng Quản trị Linux: Service and boot loader management

Đặng Thanh Bình

Service and Boot Loader Management

• Boot sequence • Runlevels • Bootloader configuration • What is the “init system”? • System V • Upstart • systemd

BOOT SEQUENCE

Boot phases

• BIOS performs integrity checks on memory and seeks instructions on the Master Boor Record (MBR).

• The MBR points to the boot loader (GRUB or LILO). • Boot loader

– asks for the OS label which will identify which

kernel to run and where it is located (hard drive and partition specified).

– loads the Linux operating system.

• The kernel executes init program

(SysV/Upstart/Systemd)

Boot phases

• SysV

/etc/rc.d/rc.sysinit

– The first processes that init starts is a script

• Upstart: Some core boot tasks started by upstart are

– Based on the appropriate run-level, scripts are executed to start various processes to run the system and make it functional.

– Plymouth - The graphical boot animation and logger

– mountall - Mounts all filesystems defined on /etc/fstab

– network* - Network related services

– Display Manager (GDM,KDM,XDM,...)

RUNLEVEL

Runlevel Concept

• A runlevel is a state, or mode, that is defined by the services listed in the directory /etc/rc.d/rc.d, where is the number of the runlevel.

• Used by SysV init system and backward compatible

by Upstart and SystemD

Runlevel Types

• Red Hat family 0 — Halt 1 — Single-user mode 2 — Not used (user-definable) 3 — Full multi-user mode 4 — Not used (user-definable) 5 — Full multi-user mode (with X-based login screen) 6 — Reboot

Runlevel Types

• Debian family (Ubuntu/Mint/...) 0 – shuts the system down. 1 – single user-mode. 2 – full multi-user mode with GUI and networking. 3-5 – The same as 2. 6 – reboots the system

Default Runlevel

• CentOS ● Default runlevel can be changed by modifying the /etc/inittab file, as following: id:5:initdefault:

• Ubuntu ● Edit /etc/init/rc-sysinit.conf and change:

• env DEFAULT_RUNLEVEL=2

● To:

• env DEFAULT_RUNLEVEL=N ● Where N is the desired runlevel.

Default Runlevel

• The runlevel can be set using kernel parameters. Edit /etc/default/grub, and change:

GRUB_CMDLINE_LINUX="

• to

GRUB_CMDLINE_LINUX="N" • where N is the runlevel you want. • Then run: sudo updategrub • You can also force a one-time boot to a different runlevel by editing the command line from the GRUB menu at boot.

Init a Runlevel

• You can init a runlevel by:

– init 5

– teleint 5

BOOT LOADER INTRODUCTION

What is a boot loader?

• Upon starting, BIOS reads the first 512 bytes of the bootable media (master boot record, or MBR). • You can store the boot record of only one OS in a

single MBR

• Hence the need for more flexible boot loaders to

support multiple operating systems

• The master boot record holds two things – Some of or all of the boot loader program

– The partition table

• Using the data stored in the MBR, the BIOS

activates the boot loader.

Boot Loaders Loading Stages

• First stage

– The BIOS loads a part of the boot loader known as the initial program loader, or IPL – The IPL interrogates the partition table and subsequently is able to load data wherever it may exist on the various media

– This action is used initially to locate the second stage boot loader, which holds the remainder of the loader.

Boot Loaders Loading Stages

• First stage

– The BIOS loads a part of the boot loader known as the initial program loader, or IPL – The IPL interrogates the partition table and subsequently is able to load data wherever it may exist on the various media

– This action is used initially to locate the second stage boot loader, which holds the remainder of the loader.

Boot Loaders In Action

• Boot loaders are usually configured in one of two

ways – As a primary boot loader – As a secondary boot loader.

• Primary boot loaders are where the first stage of

the boot loader is installed on the MBR

• Secondary boot loaders are where the first stage of the boot loader is installed onto a bootable partition. – A separate boot loader must then be installed into the MBR and configured to pass control to the secondary boot loader.

GNU GRUB

Introduction

• The GRand Unified Boot loader (GRUB) is a

choice of nowadays instead of LILO

• GNU GRUB is actively developed by the Free

Software Foundation – Based on the original GRUB program, which was

originally created by Erich Stefan Boleyn

Introduction

Original author(s) Erich Boleyn

Developer(s)

GNU Project

Initial release

1995; 20 years ago

Stable release

2.00 (GRUB 2) / June 27, 2012; 3 years ago

Preview release 2.02~beta2 (GRUB 2)/ December 24, 2013; 21 months ago

Development status Active

Written in Assembly, C

Operating system

Linux, OS X, BSD, Solaris (x86 port) and Windows (through chainloading)

Platform IA-32, x86-64, IA-64, ARM, PowerPC, MIPS and SPARC

Available in English and others

Bootloader Type

GNU GPL version 3 License

20 Website www.gnu.org/software/grub/

CONFIGURE GRUB 1

Changing boot menu

● You should edit /boot/grub/grub.conf file

● How about /boot/grub/menu.lst file? It's a

symlink to the grub.conf file.

● These files are initially created by anaconda

during the install. This is logged in /var/log/anaconda.program.log.

● We can see that this anaconda execution

uses grub.conf, not menu.lst

/var/log/anaconda.program.log

13:00:23,089 INFO : Running... ['/sbin/grubinstall', 'justcopy']

13:00:23,134 INFO : Running... ['/sbin/grub', 'batch', 'no floppy', 'devicemap=/boot/grub/device.map']

13:00:23,346 INFO :

13:00:23,347 INFO :

13:00:23,347 INFO : GNU GRUB version 0.97 (640K lower / 3072K upper memory)

13:00:23,347 INFO :

13:00:23,348 INFO : [ Minimal BASHlike line editing is supported. For the first word, TAB

13:00:23,348 INFO : lists possible command completions. Anywhere else TAB lists the possible

13:00:23,348 INFO : completions of a device/filename.]

13:00:23,348 INFO : grub> root (hd0,0)

13:00:23,348 INFO : Filesystem type is ext2fs, partition type 0x83

13:00:23,348 INFO : grub> install stage2=/boot/grub/stage2 /boot/grub/stage1 d (hd0) /boot/grub/stage2 p (hd0,0)/boot/grub/grub.conf

13:00:23,348 INFO : grub>

Configure GRUB - /boot/grub/grub.conf

Options

● default= option signals to GRUB which image to boot from by default after the timeout period.

● This relates to one of the images in the

grub.conf file. 0 is the first specified, 1 is the second specified, etc.

● If you don't specify this option in the

configuration file, it will boot the first image specified in the file.

Options

● timeout= is the number of seconds the boot

prompt will wait before automatically loading the default OS, in this case, Red Hat Linux.

● splashimage= is the location of the image to

be used as the background for the GRUB GUI.

Options

● password option specifies the MD5-encrypted

password used to gain access to GRUB's interactive boot options

– This does not stop users loading your defined OS

● To generate an md5 password, run the tool grub- md5-crypt (as root), which comes with GRUB. It will

– prompt for the password you want to encrypt

– output the MD5-encrypted password

● Copy this into grub.conf after password --md5 but

on the same line

Options

● title identifies the specific OS that will be

booted from at the user interface at runtime

– Spaces could be included in this name.

● password is set in the same way as the

password above

– Do not set this password to the root password if you are planning on sharing this machine with other users.

Options

● root option tells GRUB where the OS file

system actually lives

● GRUB references the media in a different

way than LILO

– In LILO, /dev/hdb3 is the third partition of the

second disk

– Grub references this disk as (hd1,2), again the third partition of the second disk (disk 0 being the first disk, partition 0 being the first partition).

Options

● kernel: vmlinuz-X.X.XX-XX is the name of the

default boot kernel image within root directory.

● initrd: initrd-X.X.XX-XX.img is the name of the default initrd file within root directory.

– initrd enables loading a RAM disk by the boot

loader

– Allow system startup in 2 phases:

● Kernel comes up with a minimal set of compiled-in

drivers

● Additional modules are loaded from initrd

Options

● rootnoverify option tells GRUB to not try to

vary the root of the OS. This saves load errors if the file system is not a supported by GRUB.

● chainloader +1 tells GRUB to use a chain

loader to load this OS, which is required for loading Windows.

Additional Configuration At Boot Time

• Press the P key to enter your GRUB password • For edit commands before booting, press E

– This allows user to edit the specific options for the

currently highlighted OS

– If you need to access the machine in single-user mode (giving you root access without specifying a password!), select the Linux OS at the GRUB main screen. • Press E and move to the kernel line • Append single to the end of this line • Press B to boot using changed grub.conf

– Any changes you make in edit mode are not saved to

the grub.conf file

Additional Configuration At Boot Time

● To modify kernel arguments, press A

● To get to a BASH-like command-line

interface, press C

CONFIGURE GRUB 2

No Traditional Ubuntu

• Classical versions of Ubuntu used menu.lst as

configuration file

• What is “classical”? ==> GRUB1 and earlier

ones

• GRUB 2 uses /boot/grub/grub.cfg file • You shouldn’t edit this file by hand! This file is

just for GRUB2’s own usage

• sudo update-grub to automatically create

this file

update-grub command

• update-grub is a stub for running

grubmkconfig o /boot/grub/grub.cfg

• to generate a grub2 config file.

What to do?

● Two steps:

1.Edit the /etc/default/grub file

2.Run the sudo update-grub command

• How?

– When you run the update-grub command,

GRUB automatically combines ● the settings from the /etc/default/grub file ● the scripts from the /etc/grub.d/ directory ● and everything else

– to automatically create /boot/grub/grub.cfg

Edit the GRUB2 Configuration File

● gksu gedit /etc/default/grub

What to Focus?

● Save a Default Operating System:

– If you choose GRUB_DEFAULT=saved

– You also need to add a GRUB_SAVEDEFAULT=true line

What to Focus?

● Choose Whether GRUB is Hidden:

– Set GRUB_HIDDEN_TIMEOUT=0

or splash screen for 5 secs, during which you can press any key to view the menu

– If the number is 5, GRUB will display an empty screen

comment the line out — just add a # before it so that it reads #GRUB_HIDDEN_TIMEOUT=0 .

– To prevent GRUB from being automatically hidden,

What to Focus?

● Choose a Background Image:

– By default, GRUB uses a white-on-black monochrome look

– The GRUB_BACKGROUND line controls whether a

background image is used

– You can edit like this

GRUB_BACKGROUND=”/home/user/Pics/background.png”

– GRUB supports JPG/JPEG images, but these are limited to

256 colors

– Instead, you’ll probably want to use a PNG image that can

have any number of colors

– You could also use a TGA image file.

Make Your Changes Take Effect

● Save what u did to the /etc/default/grub file

● Run sudo update-grub command

●

GRUB CUSTOMIZER

What is Grub Customizer?

● Edit the menu entries (reorder, rename, add or remove)

● Edit the contents of menu entries or create new ones

(internally it edits the 40_custom)

● Change the default boot entry

● Change menu visibility and timeout

● Disable recovery entries

● Change GRUB resolution, menu colors or background

image

● GRUB repair & configuration using a Live CD

● Advanced options like booting an ISO, changing kernel

parameters and lots more

Install Grub Customizer

● sudo add-apt-repository

ppa:danielrichter2007/grub-customizer

● sudo apt-get update

● sudo apt-get install grub-customizer

Use Grub Customizer

● It has a Graphical User Interface, try it by

yourself

INIT SYSTEM

What is an “init system”?

• It's the system that launches all other systems on

your machine.

• When you boot Linux, the init system do such

things:

– loads the drivers you need

– turns on your network connection

– fires up the necessary system service

– then loads the desktop

• Without an init system, you have no way to do

anything.

What is an “init system”?

• Previous versions of Ubuntu (from 9.10 to 14.10) used a homegrown system called Upstart, which was Ubuntu's attempt to create an init to replace SysV.

• However, Ubuntu

remains a Debian to derivative and with Debian moving systemd, Ubuntu has no choice other than jumping to the systemd boat.

SYSTEM V (SYSTEM 5)

System V

• The SysV init runlevel system provides a for controlling which launches or halts when

init

standard process programs initializing a runlevel.

• SysV init was chosen because it is easier to use and more flexible than the traditional BSD-style init process.

System V

init are

• The configuration files for SysV located in the /etc/rc.d/ directory.

• Within this directory, are the rc, rc.local, rc.sysinit, and, optionally, the rc.serial scripts as well as the following directories:

init.d/ rc0.d/ rc1.d/ rc2.d/ rc3.d/ rc4.d/ rc5.d/ rc6.d/ • The init.d/ directory contains the scripts used by the /sbin/init command when controlling services.

System V Commands

• service frobozz start/stop/restart/status • ls /etc/rc.d/init.d/ • chkconfig frobozz on/off • chkconfig frobozz • chkconfig list • chkconfig list | grep httpd • chkconfig level 35 httpd on • chkconfig level 2345 postfix off • runlevel (view previuos and current runlevel) • init 0 • telinit 0

System V Commands

• update-rc.d - install and remove System-V style init script links • Syntax:

– updaterc.d [n] [f] name remove

– updaterc.d [n] name defaults [NN | SS KK]

– updaterc.d [n] name start|stop NN runlevel [runlevel]... . start|stop NN runlevel [runlevel]... . ...

– updaterc.d [n] name disable|enable [S|2|3|4|5]

● Options:

– -n Don't do anything, just show what we would do.

– -f Force removal of symlinks even if /etc/init.d/name still

exists.

System V Commands

Insert links using the defaults: updaterc.d foobar defaults

update-rc.d samples • • Equivalent command using explicit argument sets: updaterc.d foobar start 20 2 3 4 5 . stop 20 0 1 6 . •

Insert links at default runlevels when B requires A

updaterc.d script_for_A defaults 80 20

updaterc.d script_for_B defaults 90 10 • Disabling a service:

updaterc.d f foobar remove

•

Installing a system initialization-and-shutdown script: updaterc.d foobar start 45 S . stop 31 0 6 .

updaterc.d foobar stop 20 2 3 4 5 .

UPSTART

Intro

• System V init daemon (SysVinit) does not deal

well with modern hardware, including

– hotplug devices

– USB hard and flash drives

– network-mounted filesystems

• Ubuntu replaced

it with the Upstart

init

daemon

– upstart.ubuntu.com

– upstart.ubuntu.com/wiki

Reliability

• Upstart is written using the NIH Utility Library ("libnih").

– a very small, efficient and safe library of generic

routines

– designed for applications that run early in the boot

sequence ("plumbing").

• Reliability and safety is critically important for an init

daemon since:

– it runs as the super-user.

– it is responsible for managing critical system

services.

– if init exits for any reason, the kernel panics.

Differences to SysV

• SysVinit

uses

daemon

runlevels (recovery/single-user, multiuser, and more) and links from the /etc/rc?.d directories to the init scripts in /etc/init.d to start and stop system services

• The event-based Upstart init daemon uses

events to start and stop system services.

Differences to SysV

• Entries in the /etc/init directory will replace the contents of the /etc/init.d and /etc/rc?.d directories

• Runlevels will no longer be a formal feature of Ubuntu, although they will be maintained for compatibility with third-party software.

• Eventually Upstart will also replace crond.

Software package

in one

is contained The Upstart system package, which is installed by default: • upstart — Provides the Upstart init daemon

and initctl utility.

Definition

• Jobs

– A job is a series of instructions that init reads

– Categorized into tasks and services

• Task

waiting state when it is done.

– A task is a job that performs its work and returns to a

event that triggered it until the program it specifies is finished running

– A task blocks the program/process that emitted the

Definition

• Service

itself.

– A service is a job that does not normally terminate by

– The init daemon monitors each service, restarting the service if it fails and killing the service if it is stopped either manually or by an event.

– A service blocks the program/process that emitted the event that triggered it until the program it specifies has started running.

• initctl

Upstart init daemon

– The initctl (init control) utility communicates with the

initctl Examples

• To get the version of

• To start/stop/restart/reload a

job/service

the init daemon # initctl version • To set the log priority # initctl debug

# initctl info

#initctl start/stop/restart/reload JOB • To get the status of a service/job # initctl status JOB • To list all the initctl controlled

# initctl message

# initctl warn

# initctl error

# initctl fatal

services/jobs # initctl list • To reload the configuration file # initctl reloadconfiguration JOB

A Test Job

• sudo nano /etc/init/testjob.conf description "A test job file"

author "Your Name"

start on runlevel [2345]

Job

ran

'date'

Test echo exec /var/log/testjob.log • Save and close this file. • initcheckconf /etc/init/testjob.conf • sudo service testjob start • cat /var/log/testjob.log

SYSTEMD

systemd

• systemd is a system and service manager for Linux. • Compatible with SysV and LSB init scripts. • It can work as a drop-in replacement for sysvinit. • Systemd

– Provides aggressive parallelization capabilities

– Uses socket and D-Bus activation for starting services

– Offers on-demand starting of daemons

– Implements transactional dependency-based service

control logic

– Tracks processes using Linux cgroups

– Supports snapshotting and restoring

– Maintains mount and automount points

Systemd Components

System Init Daemon

• Ubuntu 15.04 (using Systemd by default):

– Systemd runs with PID 1 as /sbin/init.

– Upstart runs with PID 1 as /sbin/upstart.

• Prior versions (using Upstart by default):

– Upstart runs with PID 1 as /sbin/init.

– Systemd runs with PID 1 as

/lib/systemd/systemd.

High-level startup concept

• Upstart's model for starting processes (jobs) is "greedy

event-based"

– all available jobs whose startup events happen are

started as early as possible.

• systemd's model for starting processes (units) is "lazy

dependency-based", i. e. a unit will only start if and when some other starting unit depends on it

• During boot, systemd starts a "root unit" (default.target,

can be overridden in grub), which then transitively expands and starts its dependencies

• A new unit needs to add itself as a dependency of a unit of the boot sequence (commonly multi-user.target) in order to become active.

Commands

Operation Upstart Command Systemd equivalent

Start service start $job systemctl start $unit

Stop service stop $job systemctl stop $unit

Restart service restart $job systemctl restart $unit

initctl list systemctl status

See status of services

systemd-analyze verify

Check configuration is valid init- checkconf /tmp/foo.c onf

initctl list-env systemctl show-environment

Show job environment

initctl set- env foo=bar systemctl set- environment foo=bar

Set job environment variable

Commands

Operation Upstart Command Systemd equivalent

initctl unset- env foo systemctl unset- environment foo

Remove job environment variable

View job log sudo journalctl -u $unit

cat /var/log/upstart /$job.log

sudo journalctl -u $unit -f

tail -f job log

tail - f /var/log/upstart/ $job.log

initctl2dot

systemctl list- dependencies --all

Show relationship between services

Example Upstart Service

• /etc/init/foo.conf: # description "Job that runs the foo daemon"

# start in normal runlevels when disks are mounted and networking is available start on runlevel [2345]

# stop on shutdown/halt, singleuser mode and reboot stop on runlevel [016]

env statedir=/var/cache/foo

# create a directory needed by the daemon prestart exec mkdir p "$statedir"

exec /usr/bin/foodaemon arg1 "hello world" statedir "$statedir"

Example Systemd service

• /lib/systemd/system/foo.service: [Unit] Description=Job that runs the foo daemon Documentation=man:foo(1)

[Service] Type=forking Environment=statedir=/var/cache/foo ExecStartPre=/usr/bin/mkdir p ${statedir} ExecStart=/usr/bin/foodaemon arg1 "hello world" statedir ${statedir}

[Install] WantedBy=multiuser.target