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  • Đặng Thanh Bình

    Service and Boot Loader Management

  • Contents• 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

    – The first processes that init starts is a script /etc/rc.d/rc.sysinit

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

    • Upstart: Some core boot tasks started by upstart are– 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

  • 7

    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

  • 8

    Runlevel Types• Red Hat family0 — 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

  • 9

    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

  • 10

    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.

  • 11

    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.

  • 12

    Init a Runlevel

    • You can init a runlevel by:– init 5

    – teleint 5

  • BOOT LOADER INTRODUCTION

  • 14

    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.

  • 15

    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.

  • 16

    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.

  • 17

    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

  • 19

    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

  • 20

    IntroductionOriginal 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

    Type Bootloader

    License GNU GPL version 3

    Website www.gnu.org/software/grub/

  • CONFIGURE GRUB 1

  • 22

    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

  • 23

    /var/log/anaconda.program.log13:00:23,089 INFO    : Running... ['/sbin/grubinstall', 'justcopy']

    13:00:23,134 INFO    : Running... ['/sbin/grub', 'batch', 'nofloppy', '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> 

  • 24

    Configure GRUB - /boot/grub/grub.conf

  • 25

    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.

  • 26

    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.

  • 27

    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

  • 28

    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.

  • 29

    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).

  • 30

    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

  • 31

    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.

  • 32

    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

  • 33

    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

  • 35

    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

  • 36

    update-grub command

    • update-grub is a stub for runninggrubmkconfig o /boot/grub/grub.cfg

    • to generate a grub2 config file.

  • 37

    What to do?● Two steps:

    1.Edit the /etc/default/grub file2.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

  • 38

    Edit the GRUB2 Configuration File● gksu gedit /etc/default/grub

  • 39

    What to Focus?● Save a Default Operating System:

    – If you choose GRUB_DEFAULT=saved– You also need to add a GRUB_SAVEDEFAULT=true line

  • 40

    What to Focus?● Choose Whether GRUB is Hidden:

    – Set GRUB_HIDDEN_TIMEOUT=0– If the number is 5, GRUB will display an empty screen

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

    – To prevent GRUB from being automatically hidden, comment the line out — just add a # before it so that it reads #GRUB_HIDDEN_TIMEOUT=0 .

  • 41

    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.

  • 42

    Make Your Changes Take Effect● Save what u did to the /etc/default/grub file● Run sudo update-grub command●

  • GRUB CUSTOMIZER

  • 44

    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

  • 45

    Install Grub Customizer● sudo add-apt-repository

    ppa:danielrichter2007/grub-customizer● sudo apt-get update● sudo apt-get install grub-customizer

  • 46

    Use Grub Customizer● It has a Graphical User Interface, try it by

    yourself

  • INIT SYSTEM

  • 48

    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.

  • 49

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

  • SYSTEM V (SYSTEM 5)

  • 51

    System V• The SysV init runlevel system provides a

    standard process for controlling which programs init launches or halts when initializing a runlevel.

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

  • 52

    System V• The configuration files for SysV init are

    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.

  • 53

    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

  • 54

    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.

  • 55

    System V Commandsupdate-rc.d samples• Insert links using the defaults: updaterc.d foobar defaults• 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

    updaterc.d foobar stop 20 2 3 4 5 .

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

  • UPSTART

  • 57

    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

  • 58

    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.

  • 59

    Differences to SysV• SysVinit daemon uses 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.

  • 60

    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.

  • 61

    Software packageThe Upstart system is contained in one package, which is installed by default:• upstart — Provides the Upstart init daemon

    and initctl utility.

  • 62

    Definition• Jobs

    – A job is a series of instructions that init reads– Categorized into tasks and services

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

    waiting state when it is done.– A task blocks the program/process that emitted the

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

  • 63

    Definition• Service

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

    – 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– The initctl (init control) utility communicates with the

    Upstart init daemon

  • 64

    initctl Examples• To start/stop/restart/reload a

    job/service#initctl start/stop/restart/reload JOB 

    • To get the status of a service/job # initctl status JOB 

    • To list all the initctl controlled services/jobs

    # initctl list 

    • To reload the configuration file# initctl reloadconfiguration JOB 

    • To get the version of the init daemon

    # initctl version 

    • To set the log priority# initctl debug

    # initctl info

    # initctl message

    # initctl warn

    # initctl error

    # initctl fatal 

  • 65

    A Test Job• sudo nano /etc/init/testjob.confdescription "A test job file"

    author "Your Name"

    start on runlevel [2345]

    exec  echo  Test  Job  ran  at    'date'  >> /var/log/testjob.log

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

  • SYSTEMD

  • 67

    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

  • 68

    Systemd Components

  • 69

    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.

  • 70

    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.

  • 71

    CommandsOperation 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

    See status of services

    initctl list systemctl status

    Check configuration is valid

    init-checkconf /tmp/foo.conf

    systemd-analyze verify

    Show job environment

    initctl list-env systemctl show-environment

    Set job environment variable

    initctl set-env foo=bar

    systemctl set-environment foo=bar

  • 72

    CommandsOperation Upstart Command Systemd equivalent

    Remove job environment variable

    initctl unset-env foo

    systemctl unset-environment foo

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

    sudo journalctl -u $unit

    tail -f job log

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

    sudo journalctl -u $unit -f

    Show relationship between services

    initctl2dot systemctl list-dependencies --all

  • 73

    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"

  • 74

    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

    Package Management - UbuntuContentsINTRODUCTIONIntroIntroSlide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12BOOT LOADER INTRODUCTIONWhat is a boot loader?Boot Loaders Loading StagesSlide 16Boot Loaders In ActionGNU GRUBIntroductionSlide 20Slide 21Additional Configuration At Boot TimeAdditional Configuration At Boot TimeConfigure GRUB - /boot/grub/grub.confAdditional Configuration At Boot TimeAdditional Configuration At Boot TimeAdditional Configuration At Boot TimeAdditional Configuration At Boot TimeAdditional Configuration At Boot TimeAdditional Configuration At Boot TimeAdditional Configuration At Boot TimeAdditional Configuration At Boot TimeAdditional Configuration At Boot TimeSlide 34Slide 35Slide 36Slide 37Slide 38Slide 39Slide 40Slide 41Slide 42Slide 43Slide 44Slide 45Slide 46INTRODUCTIONIntroIntroSlide 50Slide 51Slide 52Slide 53Slide 54Slide 55Slide 56Slide 57Slide 58Slide 59Slide 60Slide 61Slide 62Slide 63Slide 64Slide 65Slide 66Slide 67Slide 68Slide 69Slide 70Slide 71Slide 72Slide 73Slide 74