Difference between revisions of "Repartitioning a CompactFlash Disk for Linux"
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</syntaxhighlight> This output illustrates that <code>/dev/sda1</code> is the root filesystem, <code>/dev/sdf1</code> is an auxiliary disk mounted on <code>/media/backup</code>, and <code>/dev/sdc1</code> is not mounted. Given the results from these three commands, <code>/dev/sdc</code> is the CF disk. If <code>/dev/sdc1</code> is mounted, it should be unmounted before continuing. <br>'''Do not continue if you are not certain which device node corresponds to the CF disk.''' | </syntaxhighlight> This output illustrates that <code>/dev/sda1</code> is the root filesystem, <code>/dev/sdf1</code> is an auxiliary disk mounted on <code>/media/backup</code>, and <code>/dev/sdc1</code> is not mounted. Given the results from these three commands, <code>/dev/sdc</code> is the CF disk. If <code>/dev/sdc1</code> is mounted, it should be unmounted before continuing. <br>'''Do not continue if you are not certain which device node corresponds to the CF disk.''' | ||
# After determining the CF disk on the system, make a backup of the CF disk to ensure that it can be restored if something goes wrong during the repartitioning process. The steps below assume that <code>/dev/sdc</code> is the CF disk as determined in the example above. Replace the <code>/dev/sdc</code> occurrences with the appropriate device for your system. | # After determining the CF disk on the system, make a backup of the CF disk to ensure that it can be restored if something goes wrong during the repartitioning process. The steps below assume that <code>/dev/sdc</code> is the CF disk as determined in the example above. Replace the <code>/dev/sdc</code> occurrences with the appropriate device for your system. | ||
− | ## First, mount | + | ## First, mount the CF disk. It is important to do this manually rather than having the system auto-mount the device to prevent it from being mounted with options that will prevent a full archive from being obtained. The listing below demonstrates how to mount the CF disk to a temporary directory: <syntaxhighlight lang=bash>developer@ldc:~$ sudo mkdir /tmp/cf |
+ | developer@ldc:~$ sudo mount /dev/sdc1 /tmp/cf | ||
+ | </syntaxhighlight> After mounting, inspect the files at the mount point and verify that the filesystem is there as expected: <syntaxhighlight lang=bash> | ||
+ | developer@ldc:~$ ls /tmp/cf | ||
+ | bin boot dev etc home lib lost+found media mnt proc root sbin sys tmp usr var | ||
+ | </syntaxhighlight> | ||
+ | ## Use tar to create a gzipped tar archive of the entire flash. The following commands will create a backup archive named <code>/home/developer/rootfs-backup/rootfs_20130404.tar.gz</code>: <syntaxhighlight lang=bash> | ||
+ | developer@ldc:~$ cd /tmp/cf | ||
+ | developer@ldc:~$ sudo tar czvf ~/rootfs-backup/rootfs_20130404.tar.gz * | ||
+ | </syntaxhighlight> | ||
+ | ## Unmount the CF disk once the backup is complete:<syntaxhighlight lang=bash> | ||
+ | developer@ldc:~$ cd | ||
+ | developer@ldc:~$ sudo umount /dev/sdc1 | ||
+ | </syntaxhighlight> | ||
+ | # Start the <code>gparted</code> utility, passing the CF disk device node as an argument as shown below:<syntaxhighlight lang=bash> | ||
+ | developer@ldc:~$ sudo gparted /dev/sdc | ||
+ | </syntaxhighlight> This should bring up a window similar to the one shown in Figure 1 below. [[File:Gparted Init.png|center|frame|Figure 1: Gparted Initial View]] | ||
+ | # Hel Help |
Revision as of 12:07, 4 April 2013
Many embedded systems require writing to persistent storage during routine operation. While the journaling filesystems used on EMAC OE systems are tolerant of power failures during a write to the filesystem, it is still advantages to leave the root filesystem mounted read-only as often as possible to prevent any possibility of data loss or corruption on the root filesystem. One method to accomplish this is using a separate disk (such as an SD card) or secondary partitions on the primary storage device for any application-specific data that needs to be written to disk. This article describes the process of creating and utilizing an additional partition for data storage.
CompactFlash Partitioning
The majority of EMAC's x86-based systems utilize CompactFlash as the primary storage device. By default, EMAC OE is provided with a single ext3 partition on the CompactFlash holding the root filesystem. The most efficient method for repartitioning this type of device is using a CompactFlash card reader on a Linux PC. While command-line tools can be utilized, the application gparted
is a graphical application that works very well for resizing existing partitions. Follow the procedure below to resize the existing partition and create a secondary partition on a CompactFlash.
- Power down the target board and carefully remove the CF disk.
- Insert the CF disk into the CF reader connected to a Linux PC.
- The system will most likely bring up a window asking what to do with the device once it is detected. If this occurs, select "Do Nothing" or a similar option to indicate that the device should not be mounted.
- Determine the device node for the CF disk. There are several methods that can be used to accomplish this:
dmesg
can provide information about the disk that was reported by the kernel when it was detected as shown below.In this example,developer@ldc:~$ dmesg | tail [7414822.178026] sd 6:0:0:1: [sdc] 4001760 512-byte logical blocks: (2.04 GB/1.90 GiB) [7414822.179094] sd 6:0:0:1: [sdc] Assuming drive cache: write through [7414822.180711] sd 6:0:0:1: [sdc] Assuming drive cache: write through [7414822.180716] sdc: sdc1
sdc
is the device corresponding to the CF disk. Also note that the size reported matches the expected size for the CF disk (2 GB in this case). The output also shows that a single partition was detected on the device:sdc1
.- The
fdisk
command can also be used to list the available devices using the-l
options. Note that you may or may not have permissions to run thefdisk
command as a normal user, it may be necessary to run the command as root usingsudo
orsu
. An examplefdisk -l
output is shown below.Three devices are listed in this output:developer@ldc:~$ sudo /sbin/fdisk -l Disk /dev/sda: 500.1 GB, 500107862016 bytes 255 heads, 63 sectors/track, 60801 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Disk identifier: 0x00000000 Device Boot Start End Blocks Id System /dev/sda1 * 1 60302 484375783+ 83 Linux /dev/sda2 60303 60801 4008217+ 5 Extended /dev/sda5 60303 60801 4008186 82 Linux swap / Solaris Disk /dev/sdc: 2048 MB, 2048901120 bytes 224 heads, 56 sectors/track, 319 cylinders Units = cylinders of 12544 * 512 = 6422528 bytes Disk identifier: 0x6a5f7029 Device Boot Start End Blocks Id System /dev/sdc1 * 1 1008 6322175+ 83 Linux Disk /dev/sdf: 2000.3 GB, 2000398934016 bytes 255 heads, 63 sectors/track, 243201 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Disk identifier: 0x0b45dffc Device Boot Start End Blocks Id System /dev/sdf1 1 243201 1953512001 83 Linux
/dev/sda
,/dev/sdc
, and/dev/sdf
. Looking at the disk sizes,/dev/sdc
matches the 2 GB size of the CF card (2048 MB as listed in the output above). - After checking the
dmesg
andfdisk
output, inspect the mount locations on the system to verify that the correct disk is being used and that it has not been utilized by the system. In the example below, thegrep
command is used to search the output of themount
command for the string "/dev/sd".This output illustrates thatdeveloper@ldc:~$ mount | grep /dev/sd travis@cheeto:~$ mount | grep /dev/sd /dev/sda1 on / type ext3 (rw,errors=remount-ro) /dev/sdf1 on /media/backup type ext3 (rw)
/dev/sda1
is the root filesystem,/dev/sdf1
is an auxiliary disk mounted on/media/backup
, and/dev/sdc1
is not mounted. Given the results from these three commands,/dev/sdc
is the CF disk. If/dev/sdc1
is mounted, it should be unmounted before continuing.
Do not continue if you are not certain which device node corresponds to the CF disk.
- After determining the CF disk on the system, make a backup of the CF disk to ensure that it can be restored if something goes wrong during the repartitioning process. The steps below assume that
/dev/sdc
is the CF disk as determined in the example above. Replace the/dev/sdc
occurrences with the appropriate device for your system.- First, mount the CF disk. It is important to do this manually rather than having the system auto-mount the device to prevent it from being mounted with options that will prevent a full archive from being obtained. The listing below demonstrates how to mount the CF disk to a temporary directory: After mounting, inspect the files at the mount point and verify that the filesystem is there as expected:
developer@ldc:~$ sudo mkdir /tmp/cf developer@ldc:~$ sudo mount /dev/sdc1 /tmp/cf
developer@ldc:~$ ls /tmp/cf bin boot dev etc home lib lost+found media mnt proc root sbin sys tmp usr var
- Use tar to create a gzipped tar archive of the entire flash. The following commands will create a backup archive named
/home/developer/rootfs-backup/rootfs_20130404.tar.gz
:developer@ldc:~$ cd /tmp/cf developer@ldc:~$ sudo tar czvf ~/rootfs-backup/rootfs_20130404.tar.gz *
- Unmount the CF disk once the backup is complete:
developer@ldc:~$ cd developer@ldc:~$ sudo umount /dev/sdc1
- First, mount the CF disk. It is important to do this manually rather than having the system auto-mount the device to prevent it from being mounted with options that will prevent a full archive from being obtained. The listing below demonstrates how to mount the CF disk to a temporary directory:
- Start the
gparted
utility, passing the CF disk device node as an argument as shown below:This should bring up a window similar to the one shown in Figure 1 below.developer@ldc:~$ sudo gparted /dev/sdc
- Hel Help