Mounting a Flash Filesystem
In order to use a flash filesystem on an EMAC OE system, it must be mounted first.
Contents
There are four steps to mounting a flash filesystem on an EMAC OE machine:
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Determine which device node is assigned to the flash device.
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Determine which partition to mount.
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Determine where to mount the device.
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Mount the device.
 | NOTE: You must have root permissions to perform some of the following steps. Make sure you are logged in as the root user prior to performing the following steps. The su command can be useful for this. The filesystem will also need to be mounted read/write in order to create the directory mentioned below. See the section regarding remounting the root filesystem as read/write (above) to see how to do this. |
Determining the Device Node Assigned to the Flash Device
The easiest way to determine which device node is assigned to a particular flash device is to inspect the output of the dmesg command shortly after the device has been connected to your machine. Follow these steps to do so:
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Insert the SD, CF or microSD card or plug in the USB flash device to your EMAC OE machine.
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Wait a few seconds for the device to settle and be recognized by the OS.
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Run this command at a shell on your EMAC OE machine:
root@emac-oe:~# dmesg | tail -n 15
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Inspect the output. The output should look similar to the following:
usb 2-2: new full speed USB device using at91_ohci and address 2 usb 2-2: not running at top speed; connect to a high speed hub usb 2-2: configuration #1 chosen from 1 choice scsi0 : SCSI emulation for USB Mass Storage devices usb-storage: device found at 2 usb-storage: waiting for device to settle before scanning scsi 0:0:0:0: Direct-Access Patriot Memory PMAP PQ: 0 ANSI: 4 usb-storage: device scan complete sd 0:0:0:0: [sda] 15634432 512-byte hardware sectors: (8.00 GB/7.45 GiB) sd 0:0:0:0: [sda] Write Protect is off sd 0:0:0:0: [sda] Mode Sense: 23 00 00 00 sd 0:0:0:0: [sda] Assuming drive cache: write through sd 0:0:0:0: [sda] Assuming drive cache: write through sda: sda1 sd 0:0:0:0: [sda] Attached SCSI removable disk
Inside square brackets, we see
sda. This is the root device node assigned to our flash device.
Determine Which Partition to Mount
On a line by itself, we see:
sda: sda1
This means one partition was found on our device: sda1. This is the partition we will use.
| NOTE: If there is more than one partition, you will need to decide which partition to use based on your knowledge of the paritions on the device. The partition device node assignment will be listed in order in the output above. If the first partition is sda1, and the second one is sda5, that is not an error. Only 4 primary partitions can exist on a device. If the second partition is number 5, that means it was created as an extended partition. |
Determine Where to Mount the Device
Now that we know what device node we are going to mount, we need to determine where to mount it. The /mnt directory is typically used for this (mnt is short for mount).
Create a directory to use for the mountpoint:
root@emac-oe:~# mkdir /mnt/myflash
Alternatively, you can pick another place in the filesystem to use. Just make sure you have permission to create a directory in that location. If the directory contains files, it will still be used as the mountpoint when the mount command is issued; however, the files contained in the directory will be hidden for as long as the directory is in use as a mountpoint. This could create a great deal of confusion, so beware this potential pitfall.
| NOTE The mountpoint (where a device is mounted) is the directory which is used to host the root of the filesystem located on the partition. In other words, if this were a machine running an operating system from Microsoft, the mountpoint would be a drive letter such as D: or Z:. In Linux (and Unix), there are no drive letters. Directories are used instead. Beneficially, using directories instead of drive letters makes things more consistent (and therefore simpler) from a programming standpoint. |
Mount the Device
Now that sda1 has been determined to be the partition to mount and /mnt/myflash has been created to be used as the mountpoint, we can mount our flash device with the following command:
root@emac-oe:~# mount /dev/sda1 /mnt/myflash
If no message is returned from the above command, then it succeeded. To verify this, try the following command
root@emac-oe:~# mount | grep sda1
You should see your device listed in the output of the above command. If it is listed more than once, it may have been mounted automatically by the OS. If so, inspection of the output should show you where it was mounted.
| NOTE: If the device node was something other than sda1, then replace sda1 in the command above with the device node you determine for your flash device in the Determine Which Partition to Mount section above. |
Unmounting the Filesystem After Use
After you are finished using the flash device, you may wish to unmount it (similar to "Safely Removing" a device on other operating systems). The umount command is used for this purpose.
Continuing on with the example above, the device mounted above would be unmounted with the following command:
root@emac-oe:~# umount /mnt/myflash
If it was automounted elsewhere, it will also need to be unmounted from that mountpoint before it will be safe to remove the device. For instance, if the automounter mounted it on /media/sda1, then issue the following command:
root@emac-oe:~# umount /media/sda1
| TIP: The sync command can also be handy for ensuring data written to a device is flushed to disk prior to performing some other activity with the device. |
