1.1 Fedora TextbooksIndex

• In A Practical Guide to Fedora and Red Hat Enterprise Linux, 5th ed., by Mark Sobell, Prentice Hall, ISBN 0-13-706088-2
• Chapter 11 (pages 417 – 424, 430-1, 435)
• Chapter 15 (pages 543, 551)
• Boot Process
• Boot Loaders: Specifically GRUB
  • see also the LInux LOader: lilo
• Run Levels: display, change, etc.
• Startup Files

1.2 The InternetIndex

• Wikipedia: Booting
• We are using GRUB Legacy
  • For the latest GRUB< see GRUB Reference
• GRUB Legacy Tutorial
• GRUB Legacy Manual

5.1 A sample GRUB Legacy configuration file (version 0.9x)Index

All versions of GRUB use a configuration file under /boot/grub to display a menu of alternative operating systems to boot. Without a configuration file, GRUB starts in interactive mode and you have to specify and type everything yourself. With a configuration file, you can select from a menu list of choices.

In GRUB Legacy, each choice in the configuration file starts with a title keyword followed by a descriptive name:

# Sample GRUB menu.lst or grub.conf file (GRUB Legacy version 0.9x)
timeout=30
splashimage=(hd0,0)/grub/splash.xpm.gz
hiddenmenu
default=0

# this sdb disk has partition sdb1 for /boot and sdb2 for / (ROOT)
# (Note how pathnames do *not* start with /boot on a separate partition!)
title Fedora 2.6.31 on second disk
    root (hd1,0)
    kernel /vmlinuz-2.6.31.5-127.fc12.i686.PAE ro root=/dev/sdb2
    initrd /initramfs-2.6.31.5-127.fc12.i686.PAE.img

# this sdc disk has partition sdc1 for / (ROOT) and uses a /boot directory
# (not a separate /boot partition, so pathnames must start with /boot)
title Old Fedora 2.6.23 on third disk
    password sesame
    root (hd2,0)
    kernel /boot/vmlinuz-2.6.23.15.137.fc8 ro root=/dev/sdc1
    initrd /boot/initrd-2.6.23.15.137.fc8.img

# this first disk partition has a Windows boot loader in the first sector
title Windows on first disk
    rootnoverify (hd0,0)
    makeactive
    chainloader +1

Notes:

• The part of the file before the first title section is for general GRUB configuration options - see below for the keywords:
  • timeout: how long the menu waits before selecting the default
  • default: which title section to boot when the time-out happens
    • counts from zero – the first boot menu entry is number zero!
  • splashimage: a pretty picture to put behind the GRUB menu
  • hiddenmenu: hide the GRUB menu during the boot process
• The title boot menu entry sections for Linux kernels have these keywords:
  • root: lets you set this prefix for all following GRUB pathnames, similar to cd in the shell
    • this is not the Linux ROOT; this is the GRUB ROOT and uses GRUB device names such as (hd0,0)
    • this is prepended to all incomplete pathname references, e.g. incomplete /foo becomes complete path (hd1,0)/foo
  • kernel: the Linux kernel image followed by optional kernel options
  • initrd: the initial RAM disk to be used by the kernel at boot time
  • password: require the given password to boot this menu entry
• Windows may not be able to boot if it isn’t the first partition of the first disk! See the GRUB documentation for ways to work around this. We don’t handle Windows bugs in this course.
• Do not move or remove the GRUB configuration files! GRUB expects the files to be in a particular location on disk, and moving them may cause GRUB to fail to find them, requiring a re-install of GRUB.
  • you can edit the files in-place as long as you do not delete or move them

5.2 grub.conf keywordsIndex

• Global options (used before any title sections):
  • default n (optional): The nth title boot menu item, starting at 0, will be booted. Otherwise, the first (zeroth) title item is booted.
  • timeout 20 (optional): Number of seconds before booting into default.
  • password sesame (optional): Disable interactive editing and protect all boot menus that include the lock option
• Individual menu options (used within the title sections):
  • title: Menu title of this boot menu
  • kernel: Location of Linux kernel file, followed by options
  • lock (optional): Requires global password to boot this menu entry
  • password (optional): require the given password to boot this menu entry

Note: To find out about additional GRUB commands, type help at the GRUB shell prompt, and see the above Resources.

5.3 GRUB Device and file Naming Convention - (hd0,0)/grub/menu.lstIndex

A full GRUB path name specification is a device name (often a partition name) followed by a file system pathname inside that partition (relative to the start of the partition), e.g. (hd0,0)/grub/menu.lst where /grub/menu.lst is relative to the start of the partition (hd0,0). (This is similar to DOS/Windows and its drive letters.)

• Device names are identified by enclosing parentheses ()
• Hard disks are named hd, e.g (hd0), (hd1)
• Floppy disks are named fd, e.g. (fd0), (fd1)
• Disks and Floppies are numbered sequentially, starting at 0 (ZERO!)
• Partition numbers are given after commas, e.g. (hd0,0), (hd0,1)
• Partitions are also numbered sequentially, starting at 0 (ZERO!)
  • WARNING! Linux numbers disks starting at a! GRUB starts at ZERO.
  • WARNING! Linux numbers partitions starting at 1 (ONE)! GRUB starts at ZERO.
  • Linux sda1 is GRUB (hd0,0); Linux sdc2 is GRUB (hd2,1)
• Examples:
  • (hd0) – First recognized hard disk (any type: SCSI, ATA, USB, etc.); usually corresponds to /dev/sda
  • (fd0) – First recognized floppy diskette; usually corresponds to /dev/fd0
  • (hd0,0) – First partition on first recognized hard disk; usually corresponds to /dev/sda1
  • (hd1,4) – First logical drive on second recognized hard disk; usually corresponds to /dev/sdb5
• The GRUB root command can pre-set the device name for all following pathnames
  • e.g. “root (hd0,2)” followed by “kernel /linux” is the same as “kernel (hd0,2)/linux”

5.4 Effect of separate /boot partition on GRUB pathnamesIndex

GRUB configuration files are stored under directory /boot/grub in Linux. /boot/grub is the Linux pathname, not necessarily the GRUB pathname, because GRUB pathnames are composed of a partition name followed by a pathname inside the partition, e.g. (hd0,0)/some/path/name where /some/path/name is relative to the start of the partition.

Since partitions are mounted on directories in Linux, and those directory pathnames prefix the names inside the partition for Linux pathnames, a GRUB pathname and a Linux absolute pathname will always differ, except for the one partition that is mounted on ROOT (because prefixing an absolute pathname with / (ROOT) doesn’t change it).

5.5 Installing GRUBIndex

Your Linux installation already installed GRUB for you. If you have to re-install GRUB, you may find (or be able to install) the grub-install script that will do it for you. You can also try it manually, if the GRUB setup files are already stored under /boot/grub:

• As root, type grub at the command line: this will load GRUB and display the GRUB shell prompt grub>
• Type setup with two GRUB pathname arguments: the boot sector installation device and the device containing the GRUB setup files
  • the GRUB setup files (e.g. grub.conf) must be on the given partition
• To put GRUB into the MBR of the first disk:   setup (hd0) (hd0,0)
• Exit GRUB with the quit command when done

Most versions of the GRUB shell have TAB command completion, where you can type part of a device or pathname and GRUB will give you all the possible completions. The command-line GRUB in Fedora 12 is broken, and does not have this feature. The GRUB that runs at boot time is not broken and does have the TAB completion feature.

BE CAREFUL. GRUB does not ask you for confirmation! If you type the wrong thing, you will overwrite your boot sector with garbage and be unable to boot your system. You will need to boot a “live” CD and repair.

5.6 Booting without a GRUB menu - interactive GRUB commandsIndex

If grub.conf is not present or has been moved, GRUB cannot display a menu. In this case it will display the GRUB interactive shell, similar to what you get by typing grub at a Linux command line.

The interactive GRUB shell has its own prompt (grub>) and its own built-in commands, some with the same names as BASH shell commands. Be clear on when you are typing into the GRUB shell and when you are typing into BASH. The same command name may do different things, depending on whether GRUB executes it or BASH executes it.

Most versions of the GRUB shell have TAB command completion, where you can type part of a device or pathname and GRUB will give you all the possible completions. The command-line GRUB in Fedora 12 is broken, and does not have this feature enabled. The GRUB that runs stand-alone at boot time is not broken and does have the TAB completion feature.

Type help for a partial list of commands you can use. Some examples:

• cat - display a text file
• geometry - display information about disk partitions
• find - find which device (partition) contains a pathname
• md5crypt - prompt for and encrypt a password

At the GRUB shell prompt, GRUB commands can be entered to query the system, see text files, and load and then boot a kernel image. Examples:

grub> find /grub/grub.conf
grub> cat (hd0,0)/grub/grub.conf
grub> kernel (hd0,0)/vmlinuz ro root=/dev/sda2
grub> initrd (hd0,0)/initrd
grub> boot

Note: The GRUB shell can also be accessed by following directions (usually by pressing the letter c) when the GRUB menu is presented. [Esc] brings you from the GRUB shell back to the menu. Pressing e allows you to edit boot menu entries of grub.conf. Pressing b boots the edited menu item. Some versions of GRUB allow typing a to go directly to a GRUB kernel line and edit the options.

6.1 Booting Single User Mode (Maintenance Mode)Index

Single-user mode is a “half-up” state used for system repair and maintenance (especially for resetting the root password!). The system only brings up a minimal number of services (often none). The GUI is not started. Networking may not be enabled. Not all disks may be mounted. The console terminal gets a shell running as the root user.

To boot into single-user mode, add the word single as an option to a kernel line in a GRUB boot menu entry and then boot that entry, e.g.:

kernel (hd0,0)/vmlinuz ro root=/dev/sda3 single

6.2 Booting into a different Run LevelIndex

(Run Levels are summarized below.) To start Linux with a different Run Level than the default, add the Run Level digit to the end of the kernel options line during boot, e.g. to boot Run Level 3 (which on Fedora 12 means boot multi-user without the X11 GUI window system), use the GRUB menu to add 3 to the end of the kernel options:

kernel /vmlinuz ro root=/dev/sda2  3

6.3 Fixing a kernel panic (missing ROOT file system)Index

If you moved your ROOT file system to a different partition but forgot to change the GRUB configuration file, your kernel will “panic” and tell you it can’t find the ROOT file system. You can reboot into the GRUB shell and edit the root= option on the kernel line to point to the correct ROOT partition:

kernel (hd0,0)/vmlinuz ro root=/dev/sdb2

• FoxTrot Kernel Panic

7.1 Default Run Level in /etc/inittabIndex

• The default Run Level to use at boot time is set by the initdefault option of the /etc/inittab file. It looks like this if your default Run Level is number 5:

    id:5:initdefault:

7.2 Display Run LevelIndex

To display previous and current system Run Levels, use the runlevel command:

$ runlevel
N 5

An N will be printed as the previous Run Level right after booting, otherwise the first number will be the previous run level number.

7.3 Change Run LevelIndex

Only root can tell the system to change Run Levels.

To change Run Levels (as root) use the telinit command with an argument of the desired Run Level, e.g. telinit 5

See the table of Run Levels in the comments in the /etc/inittab file to know what each Run Level number means.

You rarely need to explicitly tell the system to change Run Levels. The shutdown command is much better for shutting down and/or rebooting the system, because shutdown will send a warning message to all logged-in users.

• You can change Run Levels while the system is running using commands such as telinit, but that command doesn’t print any warning messages.

• Usually use shutdown to shut down or reboot the system, because shutdown will send a warning message to all logged-in users.

7.4 Displaying and Controlling Run Level Services with chkconfigIndex

System services are started and stopped for each Run Level. You can see which services are on and off in each of the seven Run Levels using the chkconfig command:

$ chkconfig | wc
57 456 3195                # there are 57 possible services available

$ chkconfig --list sshd
sshd            0:off   1:off   2:on    3:on    4:on    5:on    6:off

$ chkconfig | grep syslog
rsyslog         0:off   1:off   2:on    3:on    4:on    5:on    6:off

$ chkconfig
NetworkManager  0:off   1:off   2:on    3:on    4:on    5:on    6:off
abrtd           0:off   1:off   2:off   3:on    4:off   5:on    6:off
acpid           0:off   1:off   2:on    3:on    4:on    5:on    6:off
atd             0:off   1:off   2:off   3:on    4:on    5:on    6:off
auditd          0:off   1:off   2:on    3:on    4:on    5:on    6:off
avahi-daemon    0:off   1:off   2:off   3:on    4:on    5:on    6:off
bluetooth       0:off   1:off   2:off   3:on    4:on    5:on    6:off
btseed          0:off   1:off   2:off   3:off   4:off   5:off   6:off
bttrack         0:off   1:off   2:off   3:off   4:off   5:off   6:off
cpuspeed        0:off   1:on    2:on    3:on    4:on    5:on    6:off
... many more lines ...

The chkconfig output gives a list of the known services and whether each service is supposed to be turned on or off in that Run Level.

The chkconfig command cannot tell you if the service is actually and currently on or off; it only knows what should be on or off and it does not start or stop any services itself. If you want to check whether or not a service is actually running, use the ps command to look for it.

You can use shell pipelines on the output of chkconfig, for example to find out which services are enabled to start in at least one Run Level:

# chkconfig | grep ':on'
NetworkManager  0:off   1:off   2:on    3:on    4:on    5:on    6:off
abrtd           0:off   1:off   2:off   3:on    4:off   5:on    6:off
acpid           0:off   1:off   2:on    3:on    4:on    5:on    6:off
atd             0:off   1:off   2:off   3:on    4:on    5:on    6:off
auditd          0:off   1:off   2:on    3:on    4:on    5:on    6:off
avahi-daemon    0:off   1:off   2:off   3:on    4:on    5:on    6:off
bluetooth       0:off   1:off   2:off   3:on    4:off   5:off   6:off
cpuspeed        0:off   1:on    2:on    3:on    4:on    5:on    6:off
crond           0:off   1:off   2:on    3:on    4:on    5:on    6:off
cups            0:off   1:off   2:on    3:on    4:on    5:on    6:off
... many more lines ...

A common use of chkconfig is to change which services are supposed to be turned on or off in which Run Level (requires root permissions):

# chkconfig --list bluetooth
bluetooth       0:off   1:off   2:off   3:on    4:on    5:on    6:off

# chkconfig --level 45 bluetooth off

# chkconfig --list bluetooth
bluetooth       0:off   1:off   2:off   3:on    4:off   5:off   6:off

You can also completely remove (delete) a service from chkconfig so that it does not appear at all in the output. (RTFM)

7.5 Displaying and Controlling Run Level Services without chkconfigIndex

If chkconfig is not available, you can still discover and change which services run in each Run Level by knowing how the System V Run Levels system works.

Services (such as the SSH server or the HTTP server) are started using shell scripts. All the SysV-style service start-up scripts are kept in directory /etc/init.d/:

$ ls /etc/init.d/http* /etc/init.d/ssh*
/etc/init.d/httpd  /etc/init.d/sshd

$ wc /etc/init.d/http* /etc/init.d/ssh*
 119  426 3158 /etc/init.d/httpd
 234  669 4537 /etc/init.d/sshd

Symbolic links to these scripts are placed in directory /etc/rc?.d/, e.g. the services for Run Level 3 are listed under directory /etc/rc3.d:

$ ls -l /etc/rc3.d/*ssh* /etc/rc3.d/*http*
lrwxrwxrwx. 1 root root 15 2011-09-02 09:53 /etc/rc3.d/K15httpd -> ../init.d/httpd
lrwxrwxrwx. 1 root root 14 2011-09-02 09:54 /etc/rc3.d/S55sshd -> ../init.d/sshd

The symbolic links starting with S and a number start a service; the symbolic links starting with K and a number stop (“kill”) a service, e.g.

/etc/rc3.d/K15httpd      # symlink to kill the HTTP daemon in Run Level 3
/etc/rc3.d/S55sshd       # symlink to start the SSH daemon in Run Level 3

Each of those symlinks points to a script file responsible for killing or starting the indicated service. Without chkconfig, you can change what services get killed or started by manually adding or removing symlinks from the corresponding /etc/rc?.d Run Level directories.

A service is started in a Run Level by calling its SysV start-up script with a single argument of start. A service is stopped in a Run Level by calling its SysV start-up script with a single argument of stop.

Most Run Level changes that cause these scripts to run happen at boot time and system shut down, though you can use the telinit command to change Run Levels if you need to.

While is is always possible to create and remove the symbolic links in the rc?.d directories by hand (using ln -s and rm), the chkconfig command is the preferred tool for listing and manipulating these symbolic links in their Run Level directories.

7.6 Resetting symlinks for a serviceIndex

Many/most of the SysV start-up scripts in /etc/init.d contain a chkconfig comment line in the comments at the start of the script. The comment line might look something like this:

$ grep 'chkconfig' /etc/init.d/crond
# chkconfig: 2345 90 60

The above shell comment line is readable by chkconfig if you give chkconfig the reset option for that service. With reset, chkconfig will read the above line and make sure there are start/stop symlinks for the service in Run Levels 2,3,4,5 at priority 90 and 60. For example:

# chkconfig crond reset

Now chkconfig --list crond will show crond enabled in Run Levels 2,3,4,5. The crond service will start at priority 90 and stop at priority 60. You can confirm this by looking for the symlinks in all the /etc/rc?.d directories:

$ chkconfig --list crond
crond           0:off   1:off   2:on    3:on    4:on    5:on    6:off

$ ls /etc/rc?.d/*crond*
/etc/rc0.d/K60crond  /etc/rc3.d/S90crond  /etc/rc6.d/K60crond
/etc/rc1.d/K60crond  /etc/rc4.d/S90crond
/etc/rc2.d/S90crond  /etc/rc5.d/S90crond

Note: You can always add the appropriate start/stop symlinks manually in the rc?.d directories if the above procedure isn’t possible because the chkconfig command is missing. Don’t depend on chkconfig!

7.7 Starting and Stopping Services using serviceIndex

Using chkconfig to change which servers are supposed to be on or off in any Run Level does not change what services are actually and currently running (or not running). A service may have died unexpectedly, or have been stopped or started manually.

System services can be started, stopped, and reset using the service command (as root) with a service name and an appropriate command operation argument:

# service crond
Usage: /etc/init.d/crond {start|stop|status|restart|condrestart|try-restart|reload|force-reload}

# service crond status
crond (pid  1597) is running...

# service crond restart
Stopping crond:                                            [  OK  ]
Starting crond:                                            [  OK  ]

# service crond status
crond (pid  8207) is running...

All services support the start and stop commands, which are used to start and stop services when the system changes Run Levels. You can omit any commands to generate a list of what other commands are possible:

# service httpd
Usage: httpd {start|stop|restart|condrestart|reload|status|fullstatus|graceful|help|configtest}

If your system is missing the service command, you can always execute any service script directly from the /etc/init.d/ directory, passing it an argument of what function you want to perform:

# /etc/init.d/crond status
crond (pid  8207) is running...

Remember: chkconfig only specifies what services should be on or off in a Run Level. It does not start or stop any services. You can start or stop any services in any Run Level using the service command.

8.1 Unclear Future for Upstart and/or SystemdIndex

In early 2013, there is still considerable controversy on the move from booting with Upstart to booting with Systemd. Fedora and Red Hat are moving to Systemd; Debian and Ubuntu are staying with Upstart; other distributions are watching the battle to see who wins.

See these references for some background on the heated discussions:

• Systemd controversy causes a fork of UDEV
  • Gentoo developers could also potentially be joined by Debian developers in what could turn out to be a groundswell of protest against the Red Hat led developments in Systemd.
• A developer complains that Systemd is breaking promises
  • We are now being told that, contrary to what was said when udev was migrated into the systemd tree, running udev without systemd is now deprecated and untested and might go away completely. How surprising, nobody ever predicted that when it migrated in, oh wait yes we did, and were assured that we were wrong, that standalone udev would always be supported for those of us who weren’t using systemd. Way to destroy your userbase’s trust in you…
• Linus Torvald rants against the udev developers
  • Stop this crazy. FIX UDEV ALREADY, DAMMIT. […] “Two-faced lying weasel” would be the most polite thing I could say. But it almost certainly will involve a lot of cursing.
• Linus Torvald rants against the Systemd developers
  • I also call bullshit on your “it will surely be fixed when we know what’s the right fix” excuses. […] Kay, you are so full of sh*t that it’s not funny. You’re refusing to acknowledge your bugs, you refuse to fix them even when a patch is sent to you, and then you make excuses for the fact that we have to work around *your* bugs, and say that we should have done so from the very beginning.

Good luck with the future of Linux booting.