system-booting.adoc

   1 [[sysboot]]
   2 Host Bootloader
   3 ---------------
   4 ifdef::wiki[]
   5 :pve-toplevel:
   6 endif::wiki[]
   7
   8 {pve} currently uses one of two bootloaders depending on the disk setup
   9 selected in the installer.
  10
  11 For EFI Systems installed with ZFS as the root filesystem `systemd-boot` is
  12 used. All other deployments use the standard `grub` bootloader (this usually
  13 also applies to systems which are installed on top of Debian).
  14
  15 [[sysboot_installer_part_scheme]]
  16 Partitioning scheme used by the installer
  17 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  18
  19 The {pve} installer creates 3 partitions on the bootable disks selected for
  20 installation. The bootable disks are:
  21
  22 * For Installations with `ext4` or `xfs` the selected disk
  23
  24 * For ZFS installations all disks belonging to the first `vdev`:
  25 ** The first disk for RAID0
  26 ** All disks for RAID1, RAIDZ1, RAIDZ2, RAIDZ3
  27 ** The first two disks for RAID10
  28
  29 The created partitions are:
  30
  31 * a 1 MB BIOS Boot Partition (gdisk type EF02)
  32
  33 * a 512 MB EFI System Partition (ESP, gdisk type EF00)
  34
  35 * a third partition spanning the set `hdsize` parameter or the remaining space
  36     used for the chosen storage type
  37
  38 `grub` in BIOS mode (`--target i386-pc`) is installed onto the BIOS Boot
  39 Partition of all bootable disks for supporting older systems.
  40
  41
  42 [[sysboot_grub]]
  43 Grub
  44 ~~~~
  45
  46 `grub` has been the de-facto standard for booting Linux systems for many years
  47 and is quite well documented
  48 footnote:[Grub Manual https://www.gnu.org/software/grub/manual/grub/grub.html].
  49
  50 The kernel and initrd images are taken from `/boot` and its configuration file
  51 `/boot/grub/grub.cfg` gets updated by the kernel installation process.
  52
  53 Configuration
  54 ^^^^^^^^^^^^^
  55 Changes to the `grub` configuration are done via the defaults file
  56 `/etc/default/grub` or config snippets in `/etc/default/grub.d`. To regenerate
  57 the `/boot/grub/grub.cfg` after a change to the configuration run:
  58
  59 ----
  60 `update-grub`.
  61 ----
  62
  63 [[sysboot_systemd_boot]]
  64 Systemd-boot
  65 ~~~~~~~~~~~~
  66
  67 `systemd-boot` is a lightweight EFI bootloader. It reads the kernel and initrd
  68 images directly from the EFI Service Partition (ESP) where it is installed.
  69 The main advantage of directly loading the kernel from the ESP is that it does
  70 not need to reimplement the drivers for accessing the storage.  In the context
  71 of ZFS as root filesystem this means that you can use all optional features on
  72 your root pool instead of the subset which is also present in the ZFS
  73 implementation in `grub` or having to create a separate small boot-pool
  74 footnote:[Booting ZFS on root with grub https://github.com/zfsonlinux/zfs/wiki/Debian-Stretch-Root-on-ZFS].
  75
  76 In setups with redundancy (RAID1, RAID10, RAIDZ*) all bootable disks (those
  77 being part of the first `vdev`) are partitioned with an ESP. This ensures the
  78 system boots even if the first boot device fails.  The ESPs are kept in sync by
  79 a kernel postinstall hook script `/etc/kernel/postinst.d/zz-pve-efiboot`. The
  80 script copies certain kernel versions and the initrd images to `EFI/proxmox/`
  81 on the root of each ESP and creates the appropriate config files in
  82 `loader/entries/proxmox-*.conf`.
  83
  84 The following kernel versions are configured by default:
  85
  86 * the currently running kernel
  87 * the version being newly installed on package updates
  88 * the two latest kernels
  89 * the latest version of each kernel series (e.g. 4.15, 5.0).
  90
  91 The ESPs are not kept mounted during regular operation, in contrast to `grub`,
  92 which keeps an ESP mounted on `/boot/efi`. This helps to prevent filesystem
  93 corruption to the `vfat` formatted ESPs in case of a system crash, and removes
  94 the need to manually adapt `/etc/fstab` in case the primary boot device fails.
  95
  96 [[sysboot_systemd_boot_config]]
  97 Configuration
  98 ^^^^^^^^^^^^^
  99
 100 `systemd-boot` is configured via the file `loader/loader.conf` in the root
 101 directory of an EFI System Partition (ESP). See the `loader.conf(5)` manpage
 102 for details.
 103
 104 Each bootloader entry is placed in a file of its own in the directory
 105 `loader/entries/`
 106
 107 An example entry.conf looks like this (`/` refers to the root of the ESP):
 108
 109 ----
 110 title    Proxmox
 111 version  5.0.15-1-pve
 112 options   root=ZFS=rpool/ROOT/pve-1 boot=zfs
 113 linux    /EFI/proxmox/5.0.15-1-pve/vmlinuz-5.0.15-1-pve
 114 initrd   /EFI/proxmox/5.0.15-1-pve/initrd.img-5.0.15-1-pve
 115 ----
 116
 117
 118 .Manually keeping a kernel bootable
 119
 120 Should you wish to add a certain kernel and initrd image to the list of
 121 bootable kernels you need to:
 122
 123 * create a directory on the ESP (e.g. `/EFI/personalkernel`)
 124 * copy the kernel and initrd image to that directory
 125 * create a entry for this kernel in `/loader/entries/*.conf`
 126
 127 NOTE: do not use `/EFI/proxmox` as directory since all entries there can be
 128 removed by `/etc/kernel/postinst.d/zz-pve-efiboot`
 129
 130 Example (keeping kernel 5.0.15-1-pve and copying to an ESP mounted on
 131 `/mnt/esp`):
 132
 133 ----
 134 mkdir /mnt/esp/EFI/preferred-kernel
 135 cp /boot/initrd.img-5.0.15-1-pve /boot/vmlinuz-5.0.15-1-pve /mnt/esp/EFI/preferred-kernel
 136 echo -n "title Preferred Kernel
 137 version 5.0.15-1-pve
 138 linux /mnt/esp/EFI/preferred-kernel/vmlinuz-5.0.15-1-pve
 139 initrd /mnt/esp/EFI/preferred-kernel/initrd.img-5.0.15-1-pve
 140 options " > /mnt/esp/loader/entries/preferred.conf
 141 cat /etc/kernel/cmdline >> /mnt/esp/loader/entries/preferred.conf
 142 ----
 143
 144
 145 [[sysboot_systemd_boot_refresh]]
 146 .Updating the configuration on all ESPs
 147
 148 To copy and configure all bootable kernels and keep all ESPs in sync you just
 149 need to run the kernel hook script `/etc/kernel/postinst.d/zz-pve-efiboot`.
 150 (The equivalent to running `update-grub` on Systems being booted with `grub`).
 151
 152 This is necessary should you make changes to the kernel commandline, or if you
 153 want to add another ESP (e.g. when replacing a failed disk in a redundant ZFS
 154 pool).
 155
 156 [[sysboot_edit_kernel_cmdline]]
 157 Editing the kernel commandline
 158 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 159
 160 You can modify the kernel commandline in the following places, depending on the
 161 bootloarder used:
 162
 163 .Grub
 164
 165 The kernel commandline needs to be placed in the variable
 166 `GRUB_CMDLINE_LINUX_DEFAULT` in the file `/etc/default/grub`. Running
 167 `update-grub` appends its content to all `linux` entries in
 168 `/boot/grub/grub.cfg`.
 169
 170 .Systemd-boot
 171
 172 The kernel commandline needs to be placed as line in `/etc/kernel/cmdline`
 173 Running `/etc/kernel/postinst.d/zz-pve-efiboot` sets it as `option` line for
 174 all config files in `loader/entries/proxmox-*.conf`.