8.8. پیکربندی راه‌انداز اولیه

It is probably already functional, but it is always good to know how to configure and install the bootloader in case it “disappears“. This can occur after an installation or an upgrade of another operating system, such as Windows. The following information can also help you to modify the bootloader configuration if needed.

بازگشت به مقدمات Master Boot Record

رکورد راه‌انداز اصلی یا MBR اولین ۵۱۲ بایت اولین هارددیسک موجود را اشغال می‌کند و اولین چیزی است که توسط BIOS برای شناسایی برنامه‌ای که قادر به راه‌اندازی سیستم عامل باشد فراخوانی می‌گردد. به صورت کلی، راه‌انداز اولیه‌ای که در MBR نصب می‌گردد تمام محتوای قبلی را حذف می‌کند.

8.8.1. شناسایی دیسک‌ها

فرهنگ udev و /dev/

دایرکتوری /dev/ از قدیم محل نگهداری فایل‌های به اصطلاح “ویژه” بود، که نمایانگر دستگاه‌های جانبی متصل به سیستم بودند (قسمت بازگشت به مقدمات مجوزهای دسترسی به دستگاه را مشاهده کنید). در زمان‌های گذشته این دایرکتوری شامل تمام فایل‌های ویژه قابل استفاده بود. این رویکرد نقص‌های فراوانی به همراه داشت از جمله اینکه تعداد دستگاه‌هایی که یک نفر می‌توانست از آن‌ها استفاده کند را محدود می‌ساخت (به دلیل دست‌نویس بودن تمام نام‌ها) و اینکه تقریبا غیرممکن بود بفهمید کدام فایل واقعا کاربردی است.

Nowadays, the management of special files is entirely dynamic and matches better the nature of hot-swappable computer devices. The kernel cooperates with udev ( قسمت 9.11.3, “چگونگی کارکرد udev” ) to create and delete them as needed when the corresponding devices appear and disappear. For this reason, /dev/ doesn't need to be persistent and is thus a RAM-based filesystem that starts empty and contains only the relevant entries.

The kernel communicates lots of information about any newly added device and hands out a pair of major/minor numbers to identify it. With this udevd can create the special file under the name and with the permissions that it wants. It can also create aliases and perform additional actions (such as initialization or registration tasks). udevd's behavior is driven by a large set of (customizable) rules usually found in /lib/udev/rules.d/ and /etc/udev/rules.d/.

با نام‌هایی که به صورت خودکار اختصاص می‌یابند، می‌توانید یک نام یکسان برای دستگاه مشخصی تعیین کنید جدا از اینکه توسط چه اتصالی برقرار شده یا ترتیب آن به چه صورت بوده، که این عمل هنگام استفاده از درگاه‌های مختلف USB بسیار مفید است. اولین پارتیشن اولین هارددیسک می‌تواند نام /dev/sda1 را داشته باشد یا /dev/root-partition اگر آن را ترجیح دهید یا استفاده از هر دو در یک زمان چرا که udevd قادر است پیوندهای نمادین از این فایل‌ها بسازد.

In ancient times, some kernel modules did automatically load when you tried to access the corresponding device file. This is no longer the case, and the peripheral's special file no longer exists prior to loading the module; this is no big deal, since most modules are loaded on boot thanks to automatic hardware detection. But for undetectable peripherals (such as very old disk drives or PS/2 mice), this doesn't work. Consider adding the modules, floppy, psmouse and mousedev to /etc/modules or /etc/modules-load.d/ in order to force loading them on boot.

پیکربندی راه‌انداز اولیه باید هارد درایوهای مختلف با پارتیشن‌های مربوطه را شناسایی کند. لینوکس از فایل‌های ویژه “بلاک” که در /dev/ ذخیره می‌شوند به این منظور استفاده می‌کند. به این منظور، از دبیان Squeeze، شیوه نامگذاری هارد درایوها توسط کرنل لینوکس یکپارچه شده است و تمام هارد درایوها (IDE/SATA، SATA، SCSI، USB، IEEE 1394) اکنون توسط /dev/sd* شناخته می‌شوند.

هر پارتیشن با عدد مخصوص به خود روی دیسک شناسایی می‌گردد: برای نمونه، /dev/sda1 اولین پارتیشن روی اولین دیسک و /dev/sdb3 سومین پارتیشن روی دومین دیسک است.

معماری PC (یا “i386” به همراه “amd64”) تنها محدود به استفاده از قالب جدول پارتیشن “MS-DOS” بوده است، که تنها اجازه چهار پارتیشن “اولیه” روی هر دیسک را می‌دهد. برای غلبه بر این محدودیت یکی از پارتیشن‌ها باید به صورت “گسترش‌یافته” درآید و در آنجا می‌تواند شامل پارتیشن‌های “ثانویه” باشد. این پارتیشن‌های ثانویه از شماره ۵ آغاز می‌گردند. بنابراین اولیه پارتیشن ثانویه روی دیسک با /dev/sda5 شناخته می‌شود و به همین شکل ادامه می‌یابد.

Another restriction of the MS-DOS partition table format is that it only allows disks up to 2 TiB in size, which was becoming a real problem with recent disks.

A new partition table format called GPT (GUID Partition Table) loosens these constraints on the number of partitions (it allows up to 128 partitions when using standard settings) and on the size of the disks (up to 8 ZiB, which is more than 8 billion terabytes). If you intend to create many physical partitions on the same disk, you should therefore ensure that you are creating the partition table in the GPT format when partitioning your disk.

QUICK LOOK The Globally Unique Identifier (GUID)

Using GPT the partition type is represented as a 16 bytes long universally unique identifier, also known as Globally Unique Identifier (GUID), which is part of the UEFI standard (see یادداشت UEFI, جایگزینی پیشرفته برای BIOS). Compared to the hex code used to determine the partition type in the MS-DOS table format, you will have a hard time trying to remember these identifiers. Fortunately there are lists with all the IDs which you can use to create partition recipes to use with sfdisk or for preseeding the Debian installer.

→ https://en.wikipedia.org/wiki/GUID_Partition_Table#Partition_type_GUIDs

It is not always easy to remember what disk is connected to which SATA controller, or in third position in the SCSI chain, especially since the naming of hotplugged hard drives (which includes among others most SATA disks and external disks) can change from one boot to another. Fortunately, udev creates, in addition to /dev/sd*, symbolic links with a fixed name, which you could then use if you wished to identify a hard drive in a non-ambiguous manner. These symbolic links are stored in /dev/disk/by-id/. On a machine with two physical disks, for example, one could find the following:

mirexpress:/dev/disk/by-id# ls -l
total 0
lrwxrwxrwx 1 root root  9 23 jul. 08:58 ata-STM3500418AS_9VM3L3KP -> ../../sda
lrwxrwxrwx 1 root root 10 23 jul. 08:58 ata-STM3500418AS_9VM3L3KP-part1 -> ../../sda1
lrwxrwxrwx 1 root root 10 23 jul. 08:58 ata-STM3500418AS_9VM3L3KP-part2 -> ../../sda2
[...]
lrwxrwxrwx 1 root root  9 23 jul. 08:58 ata-WDC_WD5001AALS-00L3B2_WD-WCAT00241697 -> ../../sdb
lrwxrwxrwx 1 root root 10 23 jul. 08:58 ata-WDC_WD5001AALS-00L3B2_WD-WCAT00241697-part1 -> ../../sdb1
lrwxrwxrwx 1 root root 10 23 jul. 08:58 ata-WDC_WD5001AALS-00L3B2_WD-WCAT00241697-part2 -> ../../sdb2
[...]
lrwxrwxrwx 1 root root  9 23 jul. 08:58 scsi-SATA_STM3500418AS_9VM3L3KP -> ../../sda
lrwxrwxrwx 1 root root 10 23 jul. 08:58 scsi-SATA_STM3500418AS_9VM3L3KP-part1 -> ../../sda1
lrwxrwxrwx 1 root root 10 23 jul. 08:58 scsi-SATA_STM3500418AS_9VM3L3KP-part2 -> ../../sda2
[...]
lrwxrwxrwx 1 root root  9 23 jul. 08:58 scsi-SATA_WDC_WD5001AALS-_WD-WCAT00241697 -> ../../sdb
lrwxrwxrwx 1 root root 10 23 jul. 08:58 scsi-SATA_WDC_WD5001AALS-_WD-WCAT00241697-part1 -> ../../sdb1
lrwxrwxrwx 1 root root 10 23 jul. 08:58 scsi-SATA_WDC_WD5001AALS-_WD-WCAT00241697-part2 -> ../../sdb2
[...]
lrwxrwxrwx 1 root root  9 23 jul. 16:48 usb-LaCie_iamaKey_3ed00e26ccc11a-0:0 -> ../../sdc
lrwxrwxrwx 1 root root 10 23 jul. 16:48 usb-LaCie_iamaKey_3ed00e26ccc11a-0:0-part1 -> ../../sdc1
lrwxrwxrwx 1 root root 10 23 jul. 16:48 usb-LaCie_iamaKey_3ed00e26ccc11a-0:0-part2 -> ../../sdc2
[...]
lrwxrwxrwx 1 root root  9 23 jul. 08:58 wwn-0x5000c50015c4842f -> ../../sda
lrwxrwxrwx 1 root root 10 23 jul. 08:58 wwn-0x5000c50015c4842f-part1 -> ../../sda1
[...]
mirexpress:/dev/disk/by-id#

Note that some disks are listed several times (because they behave simultaneously as ATA disks and SCSI disks), but the relevant information is mainly in the model and serial numbers of the disks, from which you can find the peripheral file. While the links in /dev/disk/by-id/ are created using the device' serial number and physical path, there are more convenience links in e.g. /dev/disk/by-label/ (based on given labels), /dev/disk/by-uuid/ (based on unique identifiers, which can change when reformatting a device using mkfs.* or mkswap), /dev/disk/by-path/ (based on shortest physical path), and /dev/disk/by-partlabel/ and /dev/disk/by-partuuid/ (only partitions with GPT labels and their unique identifiers). If you use these links, e.g. in /etc/fstab, always prefer unique identifiers over labels. You can also obtain and change this information for each partition or device using the lsblk and blkid commands.

فایل‌های پیکربندی نمونه که در قسمت‌های بعدی به آن‌ها اشاره می‌شود بر اساس یک تنظیم یکسان هستند: یک دیسک SATA واحد، که اولین پارتیشن آن یک نصب قدیمی از ویندوز است و پارتیشن دوم شامل دبیان گنو/لینوکس است.

ALTERNATIVE The LILO bootloader

LILO که مخفف LInux LOader است قدیمی‌ترین راه‌انداز اولیه در لینوکس است - قدیمی اما اصیل. نشانی فیزیکی کرنل برای راه‌اندازی را روی MBR می‌نویسد، به همین دلیل هر بروزرسانی LILO یا فایل‌های پیکربندی آن باید به همراه اجرای دستور lilo باشد. فراموش کردن این امر باعث می‌شود سیستم در حالتی قرار بگیرد که نشانی کرنل قبلی پاک شده باشد و کرنل جدید نیز اکنون در MBR موجود نباشد.

فایل پیکربندی LILO با نام /etc/lilo.conf شناخته می‌شود؛ یک فایل نمونه برای پیکربندی استاندارد در ادامه آورده می‌شود.

مثال 8.4. فایل پیکربندی LILO

# The disk on which LILO should be installed.
# By indicating the disk and not a partition.
# you order LILO to be installed on the MBR.
boot=/dev/sda
# the partition that contains Debian
root=/dev/sda2
# the item to be loaded by default
default=Linux

# the most recent kernel image
image=/vmlinuz
  label=Linux
  initrd=/initrd.img
  read-only

# Old kernel (if the newly installed kernel doesn't boot)
image=/vmlinuz.old
  label=LinuxOLD
  initrd=/initrd.img.old
  read-only
  optional

# only for Linux/Windows dual boot
other=/dev/sda1
  label=Windows

As per request of the maintainer and upstream author of lilo, the bootloader has been removed in Debian 11 Bullseye and it is unlikely to make a comeback.

8.8.2. پیکربندی GRUB2

GRUB (GRand Unified Bootloader) is more recent. It is not necessary to invoke it after each update of the kernel; GRUB knows how to read the filesystems and find the position of the kernel on the disk by itself. To install it on the MBR of the first disk, simply type grub-install /dev/sda. This will overwrite the MBR, so be careful not to overwrite the wrong location. While it is also possible to install GRUB into a partition boot record, beware that it is usually a mistake and doing grub-install /dev/sda1 has not the same meaning as grub-install /dev/sda.

یادداشت نام دیسک‌ها برای GRUB

GRUB can only identify hard drives based on information provided by the BIOS. (hd0) corresponds to the first disk thus detected, (hd1) the second, etc. In most cases, this order corresponds exactly to the usual order of disks under Linux, but problems can occur when you associate SCSI and IDE disks. GRUB used to store the correspondences that it detected in the file /boot/grub/device.map. Nowadays, it avoids this problem using universally unique identifier (UUIDs) or file system labels when generating grub.cfg. However, the device map file is not obsolete yet, since it can be used to override when the current environment is different from the one on boot. If you find errors there (because you know that your BIOS detects drives in a different order), correct them manually and run grub-install again. grub-mkdevicemap can help creating a device.map file from which to start.

پارتیشن‌ها همچنین یک نام مخصوص به خود در GRUB دارند. زمانی که از پارتیشن‌های “کلاسیک” در قالب MS-DOS استفاده می‌کنید، اولین پارتیشن اولین دیسک به صورت (hd0,msdos1) برچسب‌گذاری می‌شود، دومین پارتیشن به صورت (hd0,msdos2) و الی آخر.

GRUB 2 configuration is stored in /boot/grub/grub.cfg, but this file (in Debian) is generated from others. Be careful not to modify it by hand, since such local modifications will be lost the next time update-grub is run (which may occur upon update of various packages). The most common modifications of the /boot/grub/grub.cfg file (to add command line parameters to the kernel or change the duration that the menu is displayed, for example) are made through the variables in /etc/default/grub. To add entries to the menu, you can either create a /boot/grub/custom.cfg file or modify the /etc/grub.d/40_custom file. For more complex configurations, you can modify other files in /etc/grub.d, or add to them; these scripts should return configuration snippets, possibly by making use of external programs. These scripts are the ones that will update the list of kernels to boot: 10_linux takes into consideration the installed Linux kernels; 20_linux_xen takes into account Xen virtual systems, and 30_os-prober adds other existing operating systems (Windows, OS X, Hurd), kernel images, and BIOS/EFI access options to the menu.

CAUTION error: symbol `grub_*' not found

One of the most often reported issues when using GRUB is that users get an error like error symbol `grub_calloc' not found and they are unable to boot the system anymore. Most of the time this error is caused by installing an updated version of GRUB that causes new modules in /boot/grub to be incompatible with old core images in the boot sector that your firmware jumps to when booting your machine. This happens on systems that are configured to run grub-install to a target device that is not actually the one that the firmware uses to boot your system (e.g. after replacing disks or moving them around - one can see the issue when running dpkg-reconfigure grub-pc showing the wrong target device). With the release of Debian 11 Bullseye (the change was also populated to Buster) the update process now checks for this issue and exits with an error in case it finds such a constellation.

→ https://bugs.debian.org/bug=966575#95

Setting up grub-pc (2.02+dfsg1-20+deb10u4) ...
/dev/disk/by-id/[..] does not exist, so cannot grub-install to it!
You must correct your GRUB install devices before proceeding:

  DEBIAN_FRONTEND=dialog dpkg --configure grub-pc
  dpkg --configure -a
dpkg: error processing package grub-pc (--configure):
 installed grub-pc package post-installation script subprocess returned error exit status 1

To fix the issue and continue the upgrade procedure, just follow the advice and run the commands given by the error message as root.

8.8.3. Using GRUB with EFI and Secure Boot

Using GRUB to boot either a traditional BIOS system (legacy or UEFI-CSM) or a UEFI system is quite different. Fortunately the user doesn't need to know the differences because Debian provides different packages for each purpose and the installer automatically cares about which one(s) to choose. The grub-pc package is chosen for legacy systems, where GRUB is installed into the MBR, while UEFI systems require grub-efi-arch, where GRUB is installed into the EFI System Partition (ESP). The latter requires a GTP partition table as well as an EFI partition.

→ https://wiki.debian.org/Grub2#UEFI_vs_BIOS_boot

To switch an existing system (supporting UEFI) from legacy to UEFI boot mode not only requires to switch the GRUB packages on the system, but also to adjust the partition table and the to create an EFI partition (probably including resizing existing partitions to create the necessary free space). It is therefore quite an elaborate process and we cannot cover it here. Fortunately, there are some manuals by bloggers describing the necessary procedures.

If you are using a system with “Secure Boot“ enabled and have installed shim-signed (see sidebar CULTURE Secure Boot and the shim bootloader), you must also install grub-efi-arch-signed. This package is not pulled in automatically, only if the installation of recommended package has been enabled.