Booting with a USB Root Filesystem - Revision history

Btisler: removed unnecessary command

2021-04-27T16:07:26Z

removed unnecessary command

Mgloff at 18:26, 12 April 2019

2019-04-12T18:26:25Z

Mgloff at 23:51, 5 March 2019

2019-03-05T23:51:01Z

Mgloff at 23:40, 5 March 2019

2019-03-05T23:40:33Z

Mgloff at 23:31, 5 March 2019

2019-03-05T23:31:51Z

Mgloff at 23:13, 5 March 2019

2019-03-05T23:13:39Z

Mgloff: Created page with "It is possible to boot most EMAC OE systems using a USB thumb drive as the root filesystem and to optionally load a kernel from. This method can be especially useful for updat..."

2019-03-05T18:27:43Z

Created page with "It is possible to boot most EMAC OE systems using a USB thumb drive as the root filesystem and to optionally load a kernel from. This method can be especially useful for updat..."

New page

It is possible to boot most EMAC OE systems using a USB thumb drive as the root filesystem and to optionally load a kernel from. This method can be especially useful for updating or recovering the root filesystem when a network connection or a network file server is not available. This page describes the steps required to boot into a root filesystem residing on a USB thumb drive.

__TOC__

==Prerequisites==

Some prerequisites must be met prior to being able to boot a root filesystem from a USB drive.

===USB Thumb Drive===

Any blank USB drive. If it is not blank, this process will completely wipe the data that exists on the USB drive.

===Root Filesystem===

A complete root filesystem for the EMAC OE system to boot from must be stored on the USB drive.

===Linux Host Computer===

Either a native Linux host or Windows host running a Linux virtual machine.

==Configuring the USB Thumb Drive==

In a terminal window, start the dmesg log with the follow option to watch for new devices.

{{cli | username=developer | hostname=ldc | pwd=~ | dmesg -w }}

Insert the USB drive and watch for the device to be announced.

{{clo}}
[ 2796.940110] scsi host6: usb-storage 1-1.2:1.0 
[ 2797.963442] scsi 6:0:0:0: Direct-Access Generic STORAGE DEVICE 0272 PQ: 0 ANSI: 0 
[ 2797.963905] sd 6:0:0:0: Attached scsi generic sg4 type 0 
[ 2798.269544] sd 6:0:0:0: [sdd] 7774208 512-byte logical blocks: (3.98 GB/3.71 GiB) 
[ 2798.271027] sd 6:0:0:0: [sdd] Write Protect is off 
[ 2798.271030] sd 6:0:0:0: [sdd] Mode Sense: 0b 00 00 08 
[ 2798.272502] sd 6:0:0:0: [sdd] No Caching mode page found 
[ 2798.272508] sd 6:0:0:0: [sdd] Assuming drive cache: write through 
[ 2798.279486] sdd: 
[ 2798.283834] sd 6:0:0:0: [sdd] Attached SCSI removable disk 
{{clos}}

The output of the <code>dmesg</code> command shows that the root device node for the USB drive in this case is <code>sdd</code> and no partitions. Partitions on the drive would be listed as <code>sdd1</code>, <code>sdd2</code>, etc. Inspect the output shown above to see the particular device node on the development PC where the USB drive is mounted. This will be different depending on the configuration of the development PC. The <code>/dev/</code> prefix will go before the device name, but is not shown in the output of <code>dmesg</code>. The device node will start with <code>sd</code>. The third letter will specify which of these devices is assigned to the USB drive. The number will indicate the partitions, if any. Press Ctrl and 'c' to exit dmesg.

* At this point, it is wise to double check that device node is actually the USB drive and not a hard drive in the system. Specifying the wrong device node could cause a complete loss of data on a hard drive. Continuing with <code>/dev/sdd</code> as the example device node, type the following command:

{{clo}}
{{clio | username=developer | hostname=ldc | pwd=~ | mount {{!}} grep sdd }}
/dev/sdd on /media/developer/FBF6-1988 type vfat
{{clos}}

This shows that the device node, <code>/dev/sdd</code>, is in fact the USB drive. This is because:
* It is not mounted on one of the standard Linux filesystem mountpoints, such as <code>/</code>, <code>/boot</code>, <code>/usr</code>, or <code>/home</code>.
* It '''is''' mounted in the <code>/media</code> directory, where it is expected. It may alternatively get mounted in <code>/mnt</code>, depending upon the configuration of the Linux distribution in use.

Use <code>fdisk -l</code> to inspect the device node. Use <code>sudo</code> with <code>fdisk</code> to gain the required <code>root</code> privileges to run <code>fdisk</code>

{{clo}}
{{clio | username=developer | hostname=ldc | pwd=~ | sudo fdisk -l /dev/sdd }}
'Disk /dev/sdd: 3.7 GiB, 3980394496 bytes, 7774208 sectors 
Units: sectors of 1 * 512 = 512 bytes 
Sector size (logical/physical): 512 bytes / 512 bytes 
I/O size (minimum/optimal): 512 bytes / 512 bytes 
Disklabel type: dos 
Disk identifier 0x00000000 
{{clos}}

The output of fdisk will also show information about any partitions that may exist on the USB drive. For example, a drive with a single FAT32 formatted partition will look like:
{{clo}}
Disk /dev/sdd: 3.7 GiB, 3980394496 bytes, 7774208 sectors 
Units: sectors of 1 * 512 = 512 bytes 
Sector size (logical/physical): 512 bytes / 512 bytes 
I/O size (minimum/optimal): 512 bytes / 512 bytes 
Disklabel type: dos 
Disk identifier 0xb04870e5 
 
Device Boot Start End Sectors Size Id Type 
/dev/sdd1 * 8760 14438399 14429640 3.7G c W95 FAT32 (LBA) 
{{clos}}

* As can be seen from the output of the <code>fdisk -l</code> command above, the disk is 3.7 GB in size, which corresponds with the size of the 4 GB USB drive being used in this example.

Unmount all of the USB drives partitions that were listed from the <code>mount</code> command above.

{{cli | username=developer | hostname=ldc | pwd=~ | sudo umount /dev/sdd }}

If there is a partition listed:

{{cli | username=developer | hostname=ldc | pwd=~ | sudo umount /dev/sdd1 }}

==Repartition the USB Drive==

Once the correct drive letter is determined, we will create a new Linux partition.

{{clo}}
{{clio | username=developer | hostname=ldc | pwd=~ | sudo fdisk /dev/sdd }}
 
Welcome to fdisk (util-linux 2.31.1). 
Changes will remain in memory only, until you decide to write them. 
Be careful before using the write command. 
 
 
Command (m for help) o 
Created a new DOS disklabel with disk identifier 0xe6077d37. 
 
Command (m for help) n 
Partition type 
: p primary (0 primary, 0 extended, 4 free) 
: e extended (container for logical partitions) 
Select (default p) p 
Partition number (1-4, default 1) 1 
First sector (2048-7774207, default 2048) 
Last sector, +sectors or +size{K,M,G,T,P} (2048-7774207, default 7774207) 
 
Created a new partition 1 of type 'Linux' and of size 3.7 GiB. 
 
Command (m for help) p 
Disk /dev/sdd: 3.7 GiB, 3980394496 bytes, 7774208 sectors 
Units sectors of 1 * 512 = 512 bytes 
Sector size (logical/physical) 512 bytes / 512 bytes 
I/O size (minimum/optimal) 512 bytes / 512 bytes 
Disklabel type dos 
Disk identifier 0xe6077d37 
 
Device Boot Start End Sectors Size Id Type 
/dev/sdd1 2048 7774207 7772160 3.7G 83 Linux 
 
Command (m for help) w 
The partition table has been altered. 
Calling ioctl() to re-read partition table. 
Syncing disks. 
 
{{clos}}

The fdisk commands are:

<code>o</code> - Create a new empty partition table

<code>n</code> - Create a new partition

<code>p</code> - The type of partition is a primary partition

<code>1</code> - Create the first partition

<code><ENTER></code> - Accept default start

<code><ENTER></code> - Accept default end

<code>p</code> - Print the new partition layout

<code>w</code> - Write the new partition layout and exit

==Format the Partition==

The first partition will be formatted with the ext4 filesystem.

{{cli | username=developer | hostname=ldc | pwd=~ | sudo yes {{!}} mkfs.ext4 /dev/sdd1 }}

==Mount the Partition==

The first partition of the USB drive will be mounted so that it is accessible to write to.

{{cli | username=developer | hostname=ldc | pwd=~ | sudo mkdir -p /media/card }}
{{cli | username=developer | hostname=ldc | pwd=~ | sudo mount /dev/sdd1 /media/card }}

The USB drive is now accessible through the <code>/media/card</code> directory.

==Extract Filesystem Archive==

Locate where the filesystem archive has been downloaded. If the archive is called rootfs.tar.gz and is in the users Downloads directory:

{{cli | username=developer | hostname=ldc | pwd=~ | cd /media/card }}
{{cli | username=developer | hostname=ldc | pwd=/media/card | sudo tar zxf ~/Downloads/rootfs.tar.gz }}

==Configuring the Client to Boot from USB==

===Configuring U-Boot===

Set the bootargs variable to tell the kernel to boot into the USB filesystem:

U-Boot> setenv bootargs console=${console} root=/dev/sda1 rootfstype=ext4
U-Boot> run bootargs

This line sets up the environment needed to boot from the USB drive. These options will be passed to the Linux kernel when booting it. The <code>console=${console}</code> part tells Linux to use the console setting from the U-Boot environment variable; this will usually be something along the lines of <code>console=ttyS0,115200n8</code>. The <code>root=/dev/sda1</code> directive tells Linux to instantiate with the USB block device, <code>/dev/sda1</code>, as the root filesystem. The <code>rootfstype=ext4</code> directive tells Linux that the root filesystem is of the EXT4 variety.

If the kernel is already programmed into the flash, it can be used in most cases to boot into the USB root filesystem. Execute the next line to load and run the default kernel.

U-Boot> boot

The machine should now boot, and show output on its console as it does so.

===Alternate Kernel Load===

An alternate kernel can be loaded into memory temporarily and booted if the kernel is not already programmed in the flash or a development kernel is to be tested. Also see [[ Loading_Images_with_U-Boot#Executing_kernel_from_RAM | Executing kernel from RAM ]]

U-Boot> usb start

@@ Line 202: / Line 202: @@
 Set the bootargs variable to tell the kernel to boot into the USB filesystem:
-  U-Boot> setenv bootargs console=${console} root=/dev/sda1 rootfstype=ext4 rootwait
+  U-Boot> setenv bootargs "console=${console} root=/dev/sda1 rootfstype=ext4 rootwait"
 This line sets up the environment needed to boot from the USB drive.  These options will be passed to the Linux kernel when booting it.  The <code>console=${console}</code> part tells Linux to use the console setting from the U-Boot environment variable; this will usually be something along the lines of <code>console=ttyS0,115200n8</code>.  The <code>root=/dev/sda1</code> directive tells Linux to instantiate with the USB block device, <code>/dev/sda1</code>, as the root filesystem. The <code>rootfstype=ext4</code> directive tells Linux that the root filesystem is of the EXT4 variety.

@@ Line 55: / Line 55: @@
 Use <code>fdisk -l</code> to inspect the device node. Use <code>sudo</code> with <code>fdisk</code> to gain the required <code>root</code> privileges to run <code>fdisk</code>
-{{clo}}
+{{clop}}
-{{clio | username=developer | hostname=ldc | pwd=~ | sudo fdisk -l /dev/sdd }}
+{{cliop | username=developer | hostname=ldc | pwd=~ | sudo fdisk -l /dev/sdd }}<nowiki>
-The output of fdisk will also show information about any partitions that may exist on the USB drive. For example, a drive with a single FAT32 formatted partition will look like:
+Disk /dev/sdd: 3.7 GiB, 3980394496 bytes, 7774208 sectors
-{{clo}}
+Disk model: STORAGE DEVICE
-Disk /dev/sdd: 3.7 GiB, 3980394496 bytes, 7774208 sectors <br />
+Units: sectors of 1 * 512 = 512 bytes
-Units: sectors of 1 * 512 = 512 bytes <br />
+Sector size (logical/physical): 512 bytes / 512 bytes
-Sector size (logical/physical): 512 bytes / 512 bytes <br />
+I/O size (minimum/optimal): 512 bytes / 512 bytes
-I/O size (minimum/optimal): 512 bytes / 512 bytes <br />
+Disklabel type: dos
-Disklabel type: dos <br />
+Disk identifier: 0x4fcf5773
-Disk identifier 0xb04870e5 <br />
+</nowiki>
-<br />
+{{closp}}
-Device     Boot Start      End  Sectors  Size Id Type <br />
-/dev/sdd1  *     8760 14438399 14429640  3.7G  c W95 FAT32 (LBA) <br />
+The output of fdisk will also show information about any partitions that may exist on the USB drive. For example, another drive with a single FAT32 formatted partition will look like:
-{{clos}}
+{{clop}}
 * As can be seen from the output of the <code>fdisk -l</code> command above, the disk is 3.7 GB in size, which corresponds with the size of the 4 GB USB drive being used in this example.
@@ Line 92: / Line 99: @@
 Once the correct drive letter is determined, we will create a new Linux partition.
-{{clo}}
+{{clop}}
-{{clio | username=developer | hostname=ldc | pwd=~ | sudo fdisk /dev/sdd }}
+{{cliop | username=developer | hostname=ldc | pwd=~ | sudo fdisk /dev/sdd }}<nowiki>
-<br />
-Welcome to fdisk (util-linux 2.31.1). <br />
+Welcome to fdisk (util-linux 2.33.1).
-Changes will remain in memory only, until you decide to write them. <br />
+Changes will remain in memory only, until you decide to write them.
-Be careful before using the write command. <br />
+Be careful before using the write command.
-<br />
-<br />
-Command (m for help) o <br />
+Command (m for help): o
-Created a new DOS disklabel with disk identifier 0xe6077d37. <br />
+Created a new DOS disklabel with disk identifier 0x05d5e983.
-<br />
-Command (m for help) n <br />
+Command (m for help): n
-Partition type <br />
+Partition type
-:  p   primary (0 primary, 0 extended, 4 free) <br />
+   p   primary (0 primary, 0 extended, 4 free)
-:   e   extended (container for logical partitions) <br />
+   e   extended (container for logical partitions)
-Select (default p) p <br />
+Select (default p): p
-Partition number (1-4, default 1) 1 <br />
+Partition number (1-4, default 1): 1
-First sector (2048-7774207, default 2048) <br />
+First sector (2048-7774207, default 2048):
-Last sector, +sectors or +size{K,M,G,T,P} (2048-7774207, default 7774207) <br />
+Last sector, +/-sectors or +/-size{K,M,G,T,P} (2048-7774207, default 7774207):
-<br />
-Created a new partition 1 of type 'Linux' and of size 3.7 GiB. <br />
+Created a new partition 1 of type 'Linux' and of size 3.7 GiB.
-<br />
-Command (m for help) p <br />
+Command (m for help): p
-Disk /dev/sdd: 3.7 GiB, 3980394496 bytes, 7774208 sectors <br />
+Disk /dev/sdd: 3.7 GiB, 3980394496 bytes, 7774208 sectors
-Units sectors of 1 * 512 = 512 bytes <br />
+Disk model: STORAGE DEVICE
-Sector size (logical/physical) 512 bytes / 512 bytes <br />
+Units: sectors of 1 * 512 = 512 bytes
-I/O size (minimum/optimal) 512 bytes / 512 bytes <br />
+Sector size (logical/physical): 512 bytes / 512 bytes
-Disklabel type dos <br />
+I/O size (minimum/optimal): 512 bytes / 512 bytes
-Disk identifier 0xe6077d37 <br />
+Disklabel type: dos
-<br />
+Disk identifier: 0x05d5e983
-Device     Boot Start     End Sectors  Size Id Type <br />
-/dev/sdd1        2048 7774207 7772160  3.7G 83 Linux <br />
+Device     Boot Start     End Sectors  Size Id Type
-<br />
+/dev/sdd1        2048 7774207 7772160  3.7G 83 Linux
-Command (m for help) w <br />
-The partition table has been altered. <br />
+Command (m for help): w
-Calling ioctl() to re-read partition table. <br />
+The partition table has been altered.
-Syncing disks. <br />
+Calling ioctl() to re-read partition table.
-<br />
+Syncing disks.
-{{clos}}
+</nowiki>
 The fdisk commands are:

@@ Line 174: / Line 174: @@
 The first partition of the USB drive will be mounted so that it is accessible to write to.
-{{cli | username=developer | hostname=ldc | pwd=~ | sudo mkdir -p /media/card }}
+{{clop}}
-{{cli | username=developer | hostname=ldc | pwd=~ | sudo mount /dev/sdd1 /media/card }}
+{{clio | username=developer | hostname=ldc | pwd=~ | sudo mkdir -p /media/card }}
 The USB drive is now accessible through the <code>/media/card</code> directory.
@@ Line 183: / Line 185: @@
 Locate where the filesystem archive has been downloaded. If the archive is called rootfs.tar.gz and is in the users Downloads directory:
-{{cli | username=developer | hostname=ldc | pwd=~ | cd /media/card }}
+{{clop}}
-{{cli | username=developer | hostname=ldc | pwd=/media/card | sudo tar zxf ~/Downloads/rootfs.tar.gz }}
+{{clio | username=developer | hostname=ldc | pwd=~ | cd /media/card }}
 ==Configuring the Client to Boot from USB==
@@ Line 194: / Line 202: @@
 Set the bootargs variable to tell the kernel to boot into the USB filesystem:
-  U-Boot> setenv bootargs console=${console} root=/dev/sda1 rootfstype=ext4
+  U-Boot> setenv bootargs console=${console} root=/dev/sda1 rootfstype=ext4 rootwait
   U-Boot> run bootargs

@@ Line 56: / Line 56: @@
 * It is not mounted on one of the standard Linux filesystem mountpoints, such as <code>/</code>, <code>/boot</code>, <code>/usr</code>, or <code>/home</code>.
 * It '''is''' mounted in the <code>/media</code> directory, where it is expected.  It may alternatively get mounted in <code>/mnt</code>, depending upon the configuration of the Linux distribution in use.
 Use <code>fdisk -l</code> to inspect the device node. Use <code>sudo</code> with <code>fdisk</code> to gain the required <code>root</code> privileges to run <code>fdisk</code>

@@ Line 39: / Line 39: @@
 [ 2798.283834] sd 6:0:0:0: [sdd] Attached SCSI removable disk <br />
 {{clos}}
 The output of the <code>dmesg</code> command shows that the root device node for the USB drive in this case is <code>sdd</code> and no partitions. Partitions on the drive would be listed as <code>sdd1</code>, <code>sdd2</code>, etc.  Inspect the output shown above to see the particular device node on the development PC where the USB drive is mounted. This will be different depending on the configuration of the development PC. The <code>/dev/</code> prefix will go before the device name, but is not shown in the output of <code>dmesg</code>. The device node will start with <code>sd</code>. The third letter will specify which of these devices is assigned to the USB drive. The number will indicate the partitions, if any. Press Ctrl and 'c' to exit dmesg.

@@ Line 154: / Line 154: @@
 The first partition will be formatted with the ext4 filesystem.
-{{cli | username=developer | hostname=ldc | pwd=~ | sudo yes {{!}} mkfs.ext4 /dev/sdd1 }}
+{{cli | username=developer | hostname=ldc | pwd=~ | yes {{!}} sudo mkfs.ext4 /dev/sdd1 }}
 ==Mount the Partition==
@@ Line 177: / Line 177: @@
 ===Configuring U-Boot===
 Set the bootargs variable to tell the kernel to boot into the USB filesystem:
@@ Line 182: / Line 183: @@
   U-Boot> run bootargs
-This line sets up the environment needed to boot from the USB drive.  These options will be passed to the Linux kernel when booting it.  The <code>console=${console}</code> part tells Linux to use the console setting from the U-Boot environment variable; this will usually be something along the lines of <code>console=ttyS0,115200n8</code>.  The <code>root=/dev/sda1</code> directive tells Linux to instantiate with the USB block device, <code>/dev/sda1</code>, as the root filesystem.  The <code>rootfstype=ext4</code> directive tells Linux that the root filesystem is of the EXT4 variety.
+This line sets up the environment needed to boot from the USB drive.  These options will be passed to the Linux kernel when booting it.  The <code>console=${console}</code> part tells Linux to use the console setting from the U-Boot environment variable; this will usually be something along the lines of <code>console=ttyS0,115200n8</code>.  The <code>root=/dev/sda1</code> directive tells Linux to instantiate with the USB block device, <code>/dev/sda1</code>, as the root filesystem. The <code>rootfstype=ext4</code> directive tells Linux that the root filesystem is of the EXT4 variety.
 If the kernel is already programmed into the flash, it can be used in most cases to boot into the USB root filesystem. Execute the next line to load and run the default kernel.
@@ Line 192: / Line 193: @@
 ===Alternate Kernel Load===
-An alternate kernel can be loaded into memory temporarily and booted if the kernel is not already programmed in the flash or a development kernel is to be tested. Also see [[ Loading_Images_with_U-Boot#Executing_kernel_from_RAM  | Executing kernel from RAM ]]
+An alternate kernel can be loaded into memory temporarily and booted if the kernel is not already programmed in the flash or a development kernel is to be tested. The below example assumes a kernel named zImage-test was placed in the /boot directory of the USB drive. Also see [[ Loading_Images_with_U-Boot#Executing_kernel_from_RAM  | Executing kernel from RAM ]]
   U-Boot> usb start