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`. The `pve-efiboot-tool` script assists in
  83 managing both the synced ESPs themselves and their contents.
  84
  85 The following kernel versions are configured by default:
  86
  87 * the currently running kernel
  88 * the version being newly installed on package updates
  89 * the two latest already installed kernels
  90 * the latest version of the second-to-last kernel series (e.g. 4.15, 5.0), if applicable
  91 * any manually selected kernels (see below)
  92
  93 The ESPs are not kept mounted during regular operation, in contrast to `grub`,
  94 which keeps an ESP mounted on `/boot/efi`. This helps to prevent filesystem
  95 corruption to the `vfat` formatted ESPs in case of a system crash, and removes
  96 the need to manually adapt `/etc/fstab` in case the primary boot device fails.
  97
  98 [[sysboot_systemd_boot_config]]
  99 Configuration
 100 ^^^^^^^^^^^^^
 101
 102 `systemd-boot` is configured via the file `loader/loader.conf` in the root
 103 directory of an EFI System Partition (ESP). See the `loader.conf(5)` manpage
 104 for details.
 105
 106 Each bootloader entry is placed in a file of its own in the directory
 107 `loader/entries/`
 108
 109 An example entry.conf looks like this (`/` refers to the root of the ESP):
 110
 111 ----
 112 title    Proxmox
 113 version  5.0.15-1-pve
 114 options   root=ZFS=rpool/ROOT/pve-1 boot=zfs
 115 linux    /EFI/proxmox/5.0.15-1-pve/vmlinuz-5.0.15-1-pve
 116 initrd   /EFI/proxmox/5.0.15-1-pve/initrd.img-5.0.15-1-pve
 117 ----
 118
 119
 120 .Manually keeping a kernel bootable
 121
 122 Should you wish to add a certain kernel and initrd image to the list of
 123 bootable kernel use `pve-efiboot-tool kernel add`.
 124
 125 For example run the following to add the kernel with ABI version `5.0.15-1-pve`
 126 to the list of kernels to keep installed and synced to all ESPs:
 127
 128 ----
 129 pve-efiboot-tool kernel add 5.0.15-1-pve
 130 ----
 131
 132 `pve-efiboot-tool kernel list` will list all kernel versions currently selected
 133 for booting:
 134
 135 ----
 136 # pve-efiboot-tool kernel list
 137 Manually selected kernels:
 138 5.0.15-1-pve
 139
 140 Automatically selected kernels:
 141 5.0.12-1-pve
 142 4.15.18-18-pve
 143 ----
 144
 145 Run `pve-efiboot-tool remove` to remove a kernel from the list of manually
 146 selected kernels, for example:
 147
 148 ----
 149 pve-efiboot-tool kernel remove 5.0.15-1-pve
 150 ----
 151
 152 NOTE: It's required to run `pve-efiboot-tool refresh` to update all EFI System
 153 Partitions (ESPs) after a manual kernel addition or removal from above.
 154
 155 [[sysboot_systemd_boot_setup]]
 156 .Setting up a new partition for use as synced ESP
 157
 158 To format and initialize a partition as synced ESP, e.g., after replacing a
 159 failed vdev in an rpool, or when converting an existing system that pre-dates
 160 the sync mechanism, `pve-efiboot-tool` from `pve-kernel-helpers` can be used.
 161
 162 WARNING: the `format` command will format the `<partition>`, make sure to pass
 163 in the right device/partition!
 164
 165 For example, to format an empty partition `/dev/sda2` as ESP, run the following:
 166
 167 ----
 168 pve-efiboot-tool format /dev/sda2
 169 ----
 170
 171 To setup an existing, unmounted ESP located on `/dev/sda2` for inclusion in
 172 {pve}'s kernel update synchronization mechanism, use the following:
 173
 174 ----
 175 pve-efiboot-tool init /dev/sda2
 176 ----
 177
 178 Afterwards `/etc/kernel/pve-efiboot-uuids` should contain a new line with the
 179 UUID of the newly added partition. The `init` command will also automatically
 180 trigger a refresh of all configured ESPs.
 181
 182 [[sysboot_systemd_boot_refresh]]
 183 .Updating the configuration on all ESPs
 184
 185 To copy and configure all bootable kernels and keep all ESPs listed in
 186 `/etc/kernel/pve-efiboot-uuids` in sync you just need to run:
 187
 188 ----
 189  pve-efiboot-tool refresh
 190 ----
 191 (The equivalent to running `update-grub` on Systems being booted with `grub`).
 192
 193 This is necessary should you make changes to the kernel commandline, or want to
 194 sync all kernels and initrds.
 195
 196 NOTE: Both `update-initramfs` and `apt` (when necessary) will automatically
 197 trigger a refresh.
 198
 199 [[sysboot_edit_kernel_cmdline]]
 200 Editing the kernel commandline
 201 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 202
 203 You can modify the kernel commandline in the following places, depending on the
 204 bootloarder used:
 205
 206 .Grub
 207
 208 The kernel commandline needs to be placed in the variable
 209 `GRUB_CMDLINE_LINUX_DEFAULT` in the file `/etc/default/grub`. Running
 210 `update-grub` appends its content to all `linux` entries in
 211 `/boot/grub/grub.cfg`.
 212
 213 .Systemd-boot
 214
 215 The kernel commandline needs to be placed as one line in `/etc/kernel/cmdline`.
 216 To apply your changes, run `pve-efiboot-tool·refresh`, which sets it as the
 217 `option` line for all config files in `loader/entries/proxmox-*.conf`.