Boot Pi from USB disk
Wed, Jan 2, 2019 · 4 minute readlinuxpi
Update 2019-11-17
Current versions of Raspberry Pi 4 do not support USB boot.
Tinkering with Raspberry Pi over Christmas, this note details setting Pi up to boot from USB disk.
A variant of these instructions
Some intructions (including the above) advise modifying /boot/config.txt to enable USB boot by adding program_usb_boot_mode=1
My experience is that this is not necessary, at least with recent Pi 3B+ which seems to have USB boot enabled by default.
Plus, the usb_boot_mode config directive does not seem to appear in the documentation for config.txt
# Value of 3020000a would indicate this Pi OS is capable of USB boot
root@pib:~# vcgencmd otp_dump | grep 17:
17:3020000aPlug your USB drive in and get it’s disk device name, sda in this case:
root@pib:~# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 111.8G 0 disk
mmcblk0 179:0 0 14.4G 0 disk
├─mmcblk0p1 179:1 0 43.9M 0 part /boot
└─mmcblk0p2 179:2 0 14.4G 0 part /Run parted to configure the disk with 100M partition for boot and remainder of disk as ext4.
Note: if you are reusing an old disk then you might need to delete existing partitions (using rm) first.
root@pib:~# parted /dev/sda
GNU Parted 3.2
Using /dev/sda
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) print
Model: Intenso SSD (scsi)
Disk /dev/sda: 120GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Disk Flags:
Number Start End Size Type File system Flags
(parted) mktable msdos
Warning: The existing disk label on /dev/sda will be destroyed and all data on this disk will be lost. Do you want to continue?
Yes/No? yes
(parted) mkpart primary fat32 0% 100M
(parted) mkpart primary ext4 100M 100%
(parted) print
Model: Intenso SSD (scsi)
Disk /dev/sda: 120GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Disk Flags:
Number Start End Size Type File system Flags
1 1049kB 99.6MB 98.6MB primary fat32 lba
2 99.6MB 120GB 120GB primary ext4 lba
(parted) quit
Information: You may need to update /etc/fstab.Run lsblk to check new disk configuration, sda now displays two partitions.
root@pib:~# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 111.8G 0 disk
├─sda1 8:1 0 94M 0 part
└─sda2 8:2 0 111.7G 0 part
mmcblk0 179:0 0 14.4G 0 disk
├─mmcblk0p1 179:1 0 43.9M 0 part /boot
└─mmcblk0p2 179:2 0 14.4G 0 part /Format the new disk partitions, boot as vfat and the remainder as ext4.
root@pib:~# mkfs.vfat -n BOOT -F 32 /dev/sda1
mkfs.fat 4.1 (2017-01-24)
root@pib:~# mkfs.ext4 /dev/sda2
mke2fs 1.43.4 (31-Jan-2017)
Creating filesystem with 29280768 4k blocks and 7323648 inodes
Filesystem UUID: 6be6a0dc-de1a-4f93-9ca6-b192fb5b6df6
Superblock backups stored on blocks:
32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,
4096000, 7962624, 11239424, 20480000, 23887872
Allocating group tables: done
Writing inode tables: done
Creating journal (131072 blocks): done
Writing superblocks and filesystem accounting information: doneMount the new disk partitions and install rsync (it may already be present):
root@pib:~# mkdir /mnt/target
root@pib:~# mount /dev/sda2 /mnt/target/
root@pib:~# mkdir /mnt/target/boot
root@pib:~# mount /dev/sda1 /mnt/target/boot/
root@pib:~# apt-get install rsync
Reading package lists... Done
Building dependency tree
Reading state information... Done
rsync is already the newest version (3.1.2-1+deb9u1).
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.Copy SD card to USB disk:
root@pib:~# rsync -ax --progress / /boot /mnt/target
sending incremental file list
./
bin/
bin/bash
912,712 100% 69.93MB/s 0:00:00 (xfr#1, ir-chk=1520/1542)
... snipped ...Refresh SSH server keys
root@pib:~# cd /mnt/target
root@pib:/mnt/target# mount --bind /dev dev
root@pib:/mnt/target# mount --bind /sys sys
root@pib:/mnt/target# mount --bind /proc proc
root@pib:/mnt/target# chroot /mnt/target
root@pib:/# rm /etc/ssh/ssh_host*
root@pib:/# dpkg-reconfigure openssh-server
Creating SSH2 RSA key; this may take some time ...
2048 SHA256:NDd/YHP7+k5nsS6fLNFbbEXCBUgXvs1+lFQcM5hy7BY root@pib.local.bits (RSA)
Creating SSH2 ECDSA key; this may take some time ...
256 SHA256:sD3yIMHAqjdVmfVCeTjjhk6uBaX4OOv//AX5wD9xeRA root@pib.local.bits (ECDSA)
Creating SSH2 ED25519 key; this may take some time ...
256 SHA256:Oc9q/MY3YQ3048PzsqPCGdysBVpwaWyUTaep1CnDifo root@pib.local.bits (ED25519)
Running in chroot, ignoring request.
root@pib:/# exit
exit
root@pib:/mnt/target# umount dev
root@pib:/mnt/target# umount sys
root@pib:/mnt/target# umount procRun blkid to get UUID’s of new partions (this is variation on instructions given in above link)
root@pib:/mnt/target# blkid -o export
...snipped...
DEVNAME=/dev/sda1
LABEL=BOOT
UUID=ACC2-B94D
TYPE=vfat
PARTUUID=590ea081-01
DEVNAME=/dev/sda2
UUID=6be6a0dc-de1a-4f93-9ca6-b192fb5b6df6
TYPE=ext4
PARTUUID=590ea081-02Update partition UUID’s (e.g. PARTUUID) in cmdline.txt and fstab
Note: Edit the ones on USB disk, not the originals on SD card :-)
root@pib:/mnt/target# cat /mnt/target/boot/cmdline.txt
dwc_otg.lpm_enable=0 console=serial0,115200 console=tty1 root=PARTUUID=cab20800-02 rootfstype=ext4 elevator=deadline fsck.repair=yes rootwait
root@pib:/mnt/target# vi /mnt/target/boot/cmdline.txt
root@pib:/mnt/target# cat /mnt/target/boot/cmdline.txt
dwc_otg.lpm_enable=0 console=serial0,115200 console=tty1 root=PARTUUID=590ea081-02 rootfstype=ext4 elevator=deadline fsck.repair=yes rootwait
root@pib:/mnt/target# cat /mnt/target/etc/fstab
proc /proc proc defaults 0 0
PARTUUID=cab20800-01 /boot vfat defaults 0 2
PARTUUID=cab20800-02 / ext4 defaults,noatime 0 1
# a swapfile is not a swap partition, no line here
# use dphys-swapfile swap[on|off] for that
root@pib:/mnt/target# vi /mnt/target/etc/fstab
root@pib:/mnt/target# cat /mnt/target/etc/fstab
proc /proc proc defaults 0 0
PARTUUID=590ea081-01 /boot vfat defaults 0 2
PARTUUID=590ea081-02 / ext4 defaults,noatime 0 1
# a swapfile is not a swap partition, no line here
# use dphys-swapfile swap[on|off] for thatUnmount USB disk and power off Pi
root@pib:/mnt/target# cd
root@pib:~# umount /mnt/target/boot
root@pib:~# umount /mnt/target
root@pib:~# poweroffRemove power from Pi before removing SD card …
Once SD card removed, power up Pi and it should boot from USB disk