Mounting a Flash Filesystem

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TODO: {{#todo: Complete (11.27.13-12:15->KY+);(12.04.13-23:00->MD+);(12.20.13-11:00->MW+)|Klint Youngmeyer|oe 4,oe 5,ky,Complete,md,mw}}

In order to use a flash filesystem on an EMAC OE system, it must be mounted first.

There are four steps to mounting a flash filesystem on an EMAC OE machine:

  1. Determine which device node is assigned to the flash device.

  2. Determine which partition to mount.

  3. Determine where to mount the device.

  4. Mount the device.

NOTE: You must have root permissions to perform some of the following steps. Use the su command to switch to the root user. The filesystem will also need to be mounted read/write in order to create the directory mentioned below. See Remounting a Filesystem

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.

  1. Insert the SD, CF or microSD card or plug in the USB flash device to your EMAC OE machine.

  2. Wait a few seconds for the device to settle and be recognized by the OS.

  3. Run this command at a shell on your EMAC OE machine: 

    root@emac-oe:~# dmesg | tail -n 15

  4. 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

    The highlighted line shows that the root device node for the flash device is sda containing one partition sda1.

Determine Which Partition to Mount

For this example, there is only one partition. It is possible that the flash device contains up to 4 primary partitions. If there are multiple partitions, choose the partition that contains the data that needs to be accessed. Repeat the steps below to mount the additional partitions if necessary. A partition with the number 5 (sda5) indicates an extended partition.

Determine Where to Mount the Device

Now that we know what partition we are going to mount, we need to determine where to mount it. The /mnt directory is typically used for the root mount point.

Create a directory to use for the mountpoint: 

root@emac-oe:~# mkdir /mnt/myflash

Any directory on the filesystem can be used as a mount point provided that the required permissions are obtained. If the directory used as the mount point contains files, they will be hidden when the flash device is mounted.


NOTE The mountpoint is the directory which is used to host the root of the filesystem located on the mounted 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, the flash device can be mounted 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

The device should be 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 where it was mounted.

NOTE: If the device node was something other than sda1, then replace sda1 in the command above with the correct device node for the 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. Make sure there are no terminal windows open accessing any files or directories on the mounted filesystem before unmounting.

Continuing on with the example above, the device 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.
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