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