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OP meant 512 bytes (which checks out with the math)
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edit approved Jan 28, 2018 at 19:57
mwfearnley
edit approved Jan 28, 2018 at 19:57
mwfearnley
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First, my thanks to all who contributed. I learned a few useful things.

Still, my experience is that most of these answers are somewhat incomplete, at least where CD and DVDs are concerned, notably regarding whether they are available to normal users rather than restricted to the superuser.
This is based on tests on my Linux Mageia 2.

Commands intended for the superuser can always be accessed by a normal user by prefixing them with /sbin/, or sometimes with /usr/sbin/. Now they may or may not work for a normal user.

Many may work, for a normal user, for a DVD on the DVD drive, even when it is not mounted, while they will not work for a hard disk (again when invoked as normal user).

For example /sbin/fdisk -l /dev/cdrom will work on my system and give the "geometry" of the DVD in the drive ... which is apparently mostly nonsense. But it does give the size of the DVD in bytes and in sectors, and a correct sector size (of 2048 bytes as is usual for DVD).

The same is true of /usr/sbin/gdisk -l /dev/cdrom, which give only the size in sectors of 2048 bytes.

other examples (as non-root, normal user)

$ /sbin/blockdev --getss /dev/cdrom   # DVD sector size
2048
$ /sbin/blockdev --getsize64 /dev/cdrom  # DVD byte size
5453316096

$ cat /proc/partitions  # see below
...
   8        8  416027241 sda8
  11        0    5325504 sr0
   8       16 1465138584 sdb
...

This works for the DVD drive, here called sr0, since the device for it is actually /dev/sr0, /dev/cdrom being only a symbolic link to it. The size is given in chunks of 1k.

Similarly, as normal user, the command

$ cat /sys/class/block/sr0/size
10651008

will give the size of a DVD on device /dev/sr0, in chunks of 512k512 bytes (as well as the size of other disk, even not mounted). However cat /sys/class/block/cdrom/size will not work be cause /dev/cdrom is only a symbolic link

The command df, suggested by some, gives the size of mounted partitions, not of whole disks. Furthermore, for a mounted CD or DVD it gives less than the actual size of the CD/DVD. More precisely, there are two distinct sizes one may be interested in :

  • the overall size of the device, including what is used for its internal organization. Typically that is the size of the file obtained if it is copied whole with the command dd;
  • the size of the space available (possibly only in read-only mode) to the user when it is mounted, which is always less. That is the size that is indicated by the command df.

First, my thanks to all who contributed. I learned a few useful things.

Still, my experience is that most of these answers are somewhat incomplete, at least where CD and DVDs are concerned, notably regarding whether they are available to normal users rather than restricted to the superuser.
This is based on tests on my Linux Mageia 2.

Commands intended for the superuser can always be accessed by a normal user by prefixing them with /sbin/, or sometimes with /usr/sbin/. Now they may or may not work for a normal user.

Many may work, for a normal user, for a DVD on the DVD drive, even when it is not mounted, while they will not work for a hard disk (again when invoked as normal user).

For example /sbin/fdisk -l /dev/cdrom will work on my system and give the "geometry" of the DVD in the drive ... which is apparently mostly nonsense. But it does give the size of the DVD in bytes and in sectors, and a correct sector size (of 2048 bytes as is usual for DVD).

The same is true of /usr/sbin/gdisk -l /dev/cdrom, which give only the size in sectors of 2048 bytes.

other examples (as non-root, normal user)

$ /sbin/blockdev --getss /dev/cdrom   # DVD sector size
2048
$ /sbin/blockdev --getsize64 /dev/cdrom  # DVD byte size
5453316096

$ cat /proc/partitions  # see below
...
   8        8  416027241 sda8
  11        0    5325504 sr0
   8       16 1465138584 sdb
...

This works for the DVD drive, here called sr0, since the device for it is actually /dev/sr0, /dev/cdrom being only a symbolic link to it. The size is given in chunks of 1k.

Similarly, as normal user, the command

$ cat /sys/class/block/sr0/size
10651008

will give the size of a DVD on device /dev/sr0, in chunks of 512k (as well as the size of other disk, even not mounted). However cat /sys/class/block/cdrom/size will not work be cause /dev/cdrom is only a symbolic link

The command df, suggested by some, gives the size of mounted partitions, not of whole disks. Furthermore, for a mounted CD or DVD it gives less than the actual size of the CD/DVD. More precisely, there are two distinct sizes one may be interested in :

  • the overall size of the device, including what is used for its internal organization. Typically that is the size of the file obtained if it is copied whole with the command dd;
  • the size of the space available (possibly only in read-only mode) to the user when it is mounted, which is always less. That is the size that is indicated by the command df.

First, my thanks to all who contributed. I learned a few useful things.

Still, my experience is that most of these answers are somewhat incomplete, at least where CD and DVDs are concerned, notably regarding whether they are available to normal users rather than restricted to the superuser.
This is based on tests on my Linux Mageia 2.

Commands intended for the superuser can always be accessed by a normal user by prefixing them with /sbin/, or sometimes with /usr/sbin/. Now they may or may not work for a normal user.

Many may work, for a normal user, for a DVD on the DVD drive, even when it is not mounted, while they will not work for a hard disk (again when invoked as normal user).

For example /sbin/fdisk -l /dev/cdrom will work on my system and give the "geometry" of the DVD in the drive ... which is apparently mostly nonsense. But it does give the size of the DVD in bytes and in sectors, and a correct sector size (of 2048 bytes as is usual for DVD).

The same is true of /usr/sbin/gdisk -l /dev/cdrom, which give only the size in sectors of 2048 bytes.

other examples (as non-root, normal user)

$ /sbin/blockdev --getss /dev/cdrom   # DVD sector size
2048
$ /sbin/blockdev --getsize64 /dev/cdrom  # DVD byte size
5453316096

$ cat /proc/partitions  # see below
...
   8        8  416027241 sda8
  11        0    5325504 sr0
   8       16 1465138584 sdb
...

This works for the DVD drive, here called sr0, since the device for it is actually /dev/sr0, /dev/cdrom being only a symbolic link to it. The size is given in chunks of 1k.

Similarly, as normal user, the command

$ cat /sys/class/block/sr0/size
10651008

will give the size of a DVD on device /dev/sr0, in chunks of 512 bytes (as well as the size of other disk, even not mounted). However cat /sys/class/block/cdrom/size will not work be cause /dev/cdrom is only a symbolic link

The command df, suggested by some, gives the size of mounted partitions, not of whole disks. Furthermore, for a mounted CD or DVD it gives less than the actual size of the CD/DVD. More precisely, there are two distinct sizes one may be interested in :

  • the overall size of the device, including what is used for its internal organization. Typically that is the size of the file obtained if it is copied whole with the command dd;
  • the size of the space available (possibly only in read-only mode) to the user when it is mounted, which is always less. That is the size that is indicated by the command df.
added 440 characters in body
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babou
babou
  • 888
  • 1
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  • 19

First, my thanks to all who contributed. I learned a few useful things.

Still, my experience is that most of these answers are somewhat incomplete, at least where CD and DVDs are concerned, notably regarding whether they are available to normal users rather than restricted to the superuser.
This is based on tests on my Linux Mageia 2.

Commands intended for the superuser can always be accessed by a normal user by prefixing them with /sbin/, or sometimes with /usr/sbin/. Now they may or may not work for a normal user.

Many may work, for a normal user, for a DVD on the DVD drive, even when it is not mounted, while they will not work for a hard disk (again when invoked as normal user).

For example /sbin/fdisk -l /dev/cdrom will work on my system and give the "geometry" of the DVD in the drive ... which is apparently mostly nonsense. But it does give the size of the DVD in bytes and in sectors, and a correct sector size (of 2048 bytes as is usual for DVD).

The same is true of /usr/sbin/gdisk -l /dev/cdrom, which give only the size in sectors of 2048 bytes.

other examples (as non-root, normal user)

$ /sbin/blockdev --getss /dev/cdrom   # DVD sector size
2048
$ /sbin/blockdev --getsize64 /dev/cdrom  # DVD byte size
5453316096

$ cat /proc/partitions  # see below
...
   8        8  416027241 sda8
  11        0    5325504 sr0
   8       16 1465138584 sdb
...

This works for the DVD drive, here called sr0, since the device for it is actually /dev/sr0, /dev/cdrom being only a symbolic link to it. The size is given in chunks of 1k.

Similarly, as normal user, the command

$ cat /sys/class/block/sr0/size
10651008

will give the size of a DVD on device /dev/sr0, in chunks of 512k (as well as the size of other disk, even not mounted). However cat /sys/class/block/cdrom/size will not work be cause /dev/cdrom is only a symbolic link

The command df, suggested by some, gives the size of mounted partitions, not of whole disks. Furthermore, for a mounted CD or DVD it gives less than the actual size of the CD/DVD. More precisely, there are two distinct sizes one may be interested in :

  • the overall size of the device, including what is used for its internal organization. Typically that is the size of the file obtained if it is copied whole with the command dd;
  • the size of the space available (possibly only in read-only mode) to the user when it is mounted, which is always less. That is the size that is indicated by the command df.

First, my thanks to all who contributed. I learned a few useful things.

Still, my experience is that most of these answers are somewhat incomplete, at least where CD and DVDs are concerned, notably regarding whether they are available to normal users rather than restricted to the superuser.
This is based on tests on my Linux Mageia 2.

Commands intended for the superuser can always be accessed by a normal user by prefixing them with /sbin/, or sometimes with /usr/sbin/. Now they may or may not work for a normal user.

Many may work, for a normal user, for a DVD on the DVD drive, even when it is not mounted, while they will not work for a hard disk (again when invoked as normal user).

For example /sbin/fdisk -l /dev/cdrom will work on my system and give the "geometry" of the DVD in the drive ... which is apparently mostly nonsense. But it does give the size of the DVD in bytes and in sectors, and a correct sector size (of 2048 bytes as is usual for DVD).

The same is true of /usr/sbin/gdisk -l /dev/cdrom, which give only the size in sectors of 2048 bytes.

other examples (as non-root, normal user)

$ /sbin/blockdev --getss /dev/cdrom   # DVD sector size
2048
$ /sbin/blockdev --getsize64 /dev/cdrom  # DVD byte size
5453316096

$ cat /proc/partitions  # see below
...
   8        8  416027241 sda8
  11        0    5325504 sr0
   8       16 1465138584 sdb
...

This works for the DVD drive, here called sr0, since the device for it is actually /dev/sr0, /dev/cdrom being only a symbolic link to it. The size is given in chunks of 1k.

Similarly, as normal user, the command

$ cat /sys/class/block/sr0/size
10651008

will give the size of a DVD on device /dev/sr0, in chunks of 512k (as well as the size of other disk, even not mounted). However cat /sys/class/block/cdrom/size will not work be cause /dev/cdrom is only a symbolic link

The command df, suggested by some, gives the size of mounted partitions, not of whole disks. Furthermore, for a mounted CD or DVD it gives less than the actual size of the CD/DVD.

First, my thanks to all who contributed. I learned a few useful things.

Still, my experience is that most of these answers are somewhat incomplete, at least where CD and DVDs are concerned, notably regarding whether they are available to normal users rather than restricted to the superuser.
This is based on tests on my Linux Mageia 2.

Commands intended for the superuser can always be accessed by a normal user by prefixing them with /sbin/, or sometimes with /usr/sbin/. Now they may or may not work for a normal user.

Many may work, for a normal user, for a DVD on the DVD drive, even when it is not mounted, while they will not work for a hard disk (again when invoked as normal user).

For example /sbin/fdisk -l /dev/cdrom will work on my system and give the "geometry" of the DVD in the drive ... which is apparently mostly nonsense. But it does give the size of the DVD in bytes and in sectors, and a correct sector size (of 2048 bytes as is usual for DVD).

The same is true of /usr/sbin/gdisk -l /dev/cdrom, which give only the size in sectors of 2048 bytes.

other examples (as non-root, normal user)

$ /sbin/blockdev --getss /dev/cdrom   # DVD sector size
2048
$ /sbin/blockdev --getsize64 /dev/cdrom  # DVD byte size
5453316096

$ cat /proc/partitions  # see below
...
   8        8  416027241 sda8
  11        0    5325504 sr0
   8       16 1465138584 sdb
...

This works for the DVD drive, here called sr0, since the device for it is actually /dev/sr0, /dev/cdrom being only a symbolic link to it. The size is given in chunks of 1k.

Similarly, as normal user, the command

$ cat /sys/class/block/sr0/size
10651008

will give the size of a DVD on device /dev/sr0, in chunks of 512k (as well as the size of other disk, even not mounted). However cat /sys/class/block/cdrom/size will not work be cause /dev/cdrom is only a symbolic link

The command df, suggested by some, gives the size of mounted partitions, not of whole disks. Furthermore, for a mounted CD or DVD it gives less than the actual size of the CD/DVD. More precisely, there are two distinct sizes one may be interested in :

  • the overall size of the device, including what is used for its internal organization. Typically that is the size of the file obtained if it is copied whole with the command dd;
  • the size of the space available (possibly only in read-only mode) to the user when it is mounted, which is always less. That is the size that is indicated by the command df.
Source Link
babou
babou
  • 888
  • 1
  • 12
  • 19

First, my thanks to all who contributed. I learned a few useful things.

Still, my experience is that most of these answers are somewhat incomplete, at least where CD and DVDs are concerned, notably regarding whether they are available to normal users rather than restricted to the superuser.
This is based on tests on my Linux Mageia 2.

Commands intended for the superuser can always be accessed by a normal user by prefixing them with /sbin/, or sometimes with /usr/sbin/. Now they may or may not work for a normal user.

Many may work, for a normal user, for a DVD on the DVD drive, even when it is not mounted, while they will not work for a hard disk (again when invoked as normal user).

For example /sbin/fdisk -l /dev/cdrom will work on my system and give the "geometry" of the DVD in the drive ... which is apparently mostly nonsense. But it does give the size of the DVD in bytes and in sectors, and a correct sector size (of 2048 bytes as is usual for DVD).

The same is true of /usr/sbin/gdisk -l /dev/cdrom, which give only the size in sectors of 2048 bytes.

other examples (as non-root, normal user)

$ /sbin/blockdev --getss /dev/cdrom   # DVD sector size
2048
$ /sbin/blockdev --getsize64 /dev/cdrom  # DVD byte size
5453316096

$ cat /proc/partitions  # see below
...
   8        8  416027241 sda8
  11        0    5325504 sr0
   8       16 1465138584 sdb
...

This works for the DVD drive, here called sr0, since the device for it is actually /dev/sr0, /dev/cdrom being only a symbolic link to it. The size is given in chunks of 1k.

Similarly, as normal user, the command

$ cat /sys/class/block/sr0/size
10651008

will give the size of a DVD on device /dev/sr0, in chunks of 512k (as well as the size of other disk, even not mounted). However cat /sys/class/block/cdrom/size will not work be cause /dev/cdrom is only a symbolic link

The command df, suggested by some, gives the size of mounted partitions, not of whole disks. Furthermore, for a mounted CD or DVD it gives less than the actual size of the CD/DVD.