Unable to mount 512 MG filesystem not authorized

The most common thing to be mounted is a hard drive partition. Hard drives are kept in /dev and have different names depending on what type of drive they are. IDE/ATA drives are labelled as /dev/hda, /dev/hdb, /dev/hdc and /dev/hdd (since a PC's IDE interfaces can only handle 4 devices at a time). Note that these can be devices such as IDE/ATA CDROMS, Compact Flash to IDE converters, and some special floppy drives (although they tend to appear mainly in laptops). For SCSI devices the labels are /dev/sda, /dev/sdb, /dev/sdc, /dev/sdd, /dev/sde, /dev/sdf, /dev/sdg, /dev/sdh and /dev/sdi (since a SCSI chain can contain up to nine devices). Other types of drive, such as USB, SATA, etc. are mapped to these SCSI devices by Linux. Therefore SATA and USB drives are labelled as /dev/sdX where X is a letter, starting at "a".

Since these are literally the devices you can issue a command such as:
sudo eject /dev/hdc

If /dev/hdc is a CD drive then it will eject.

In the case of hard drives, there is another abstraction. A hard drive (and many devices such as USB "sticks" which act like hard drives) can be partitioned to allow many filesystems to be stored on them. This means that the filesystems themselves are accessible via the partition labels, such as /dev/hda1 (the first partition on /dev/hda). This means that we finally know about something we can mount, a partition, since it contains a filesystem.

Another physical filesystem which can be mounted is the ISO9660 filesystem used on CDROMs. Since there is only ever one CD in a CD drive there is no point creating /dev/hdc1 (where /dev/hdc is a CDROM drive) since there is only one filesystem on it. That means that you can mount CD drive devices explicitly, so if /dev/hdc is a CDROM drive then it is possible to mount /dev/hdc if there is a disc in it.

Floppy disks only contain one filesystem, and are labeled as /dev/fd0 for the first drive, /dev/fd1 for the second drive, etc. So now we know three things which can be mounted.

Devices like USB sticks are treated like hard drives (so /dev/sda1, for example, may contain a filesystem) and so are iPods (although I think the main data on an iPod is stored on the second partition)

Mounting is not restricted to physical devices. If you have a filesystem "image" (which IS a filesystem, whether an exact copy of an existing filesystem, or a filesystem created specifically for that file) then you can mount that through the use of a fake device called the "loopback device"

How To Mount/Unmount Filesystems

Unmounting

Firstly I will tell you how to unmount any filesystem you mount after trying these commands. Unmounting is done through the "umount" command, which can be given a device or a mount point so:
sudo umount /mnt
sudo umount /dev/hda1

Would both unmount the filesystem on /dev/hda1 if it is mounted on /mnt.

Remember that a filesystem cannot be in use when it is unmounted, otherwise umount will give an error. If you know it is safe to unmount a filesystem you can use:
sudo umount -l /mountpoint

The most common thing to be mounted is a hard drive partition. Hard drives are kept in /dev and have different names depending on what type of drive they are. IDE/ATA drives are labelled as /dev/hda, /dev/hdb, /dev/hdc and /dev/hdd (since a PC's IDE interfaces can only handle 4 devices at a time). Note that these can be devices such as IDE/ATA CDROMS, Compact Flash to IDE converters, and some special floppy drives (although they tend to appear mainly in laptops). For SCSI devices the labels are /dev/sda, /dev/sdb, /dev/sdc, /dev/sdd, /dev/sde, /dev/sdf, /dev/sdg, /dev/sdh and /dev/sdi (since a SCSI chain can contain up to nine devices). Other types of drive, such as USB, SATA, etc. are mapped to these SCSI devices by Linux. Therefore SATA and USB drives are labelled as /dev/sdX where X is a letter, starting at "a".

Since these are literally the devices you can issue a command such as:
sudo eject /dev/hdc

If /dev/hdc is a CD drive then it will eject.

In the case of hard drives, there is another abstraction. A hard drive (and many devices such as USB "sticks" which act like hard drives) can be partitioned to allow many filesystems to be stored on them. This means that the filesystems themselves are accessible via the partition labels, such as /dev/hda1 (the first partition on /dev/hda). This means that we finally know about something we can mount, a partition, since it contains a filesystem.

Another physical filesystem which can be mounted is the ISO9660 filesystem used on CDROMs. Since there is only ever one CD in a CD drive there is no point creating /dev/hdc1 (where /dev/hdc is a CDROM drive) since there is only one filesystem on it. That means that you can mount CD drive devices explicitly, so if /dev/hdc is a CDROM drive then it is possible to mount /dev/hdc if there is a disc in it.

Floppy disks only contain one filesystem, and are labeled as /dev/fd0 for the first drive, /dev/fd1 for the second drive, etc. So now we know three things which can be mounted.

Devices like USB sticks are treated like hard drives (so /dev/sda1, for example, may contain a filesystem) and so are iPods (although I think the main data on an iPod is stored on the second partition)

Mounting is not restricted to physical devices. If you have a filesystem "image" (which IS a filesystem, whether an exact copy of an existing filesystem, or a filesystem created specifically for that file) then you can mount that through the use of a fake device called the "loopback device"

How To Mount/Unmount Filesystems

Unmounting

Firstly I will tell you how to unmount any filesystem you mount after trying these commands. Unmounting is done through the "umount" command, which can be given a device or a mount point so:
sudo umount /mnt
sudo umount /dev/hda1

Would both unmount the filesystem on /dev/hda1 if it is mounted on /mnt.

Remember that a filesystem cannot be in use when it is unmounted, otherwise umount will give an error. If you know it is safe to unmount a filesystem you can use:
sudo umount -l /mountpoint