fdisk command

about partitions:

• Primary partition are limited to 4.
• Extended partitions are container for logical partitions.

fdisk "fixed disk" is the traditional linux partitioning utility. Take a look at the following interactive output that creates: * loop0p1 primary partition of 10M * loop0p2 primary partition of 20M * loop0p3 primary EXTENDED partition with all remaining space * loop0p5 primary partition of 20M

root@raspbeeerry:~# fdisk /dev/loop0 

Welcome to fdisk (util-linux 2.29.2).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.

Device does not contain a recognized partition table.
Created a new DOS disklabel with disk identifier 0xd1d1a072.

Command (m for help): m

Help:

DOS (MBR)
a   toggle a bootable flag
b   edit nested BSD disklabel
c   toggle the dos compatibility flag

Generic
d   delete a partition
F   list free unpartitioned space
l   list known partition types
n   add a new partition
p   print the partition table
t   change a partition type
v   verify the partition table
i   print information about a partition

Misc
m   print this menu
u   change display/entry units
x   extra functionality (experts only)

Script
I   load disk layout from sfdisk script file
O   dump disk layout to sfdisk script file

Save & Exit
w   write table to disk and exit
q   quit without saving changes

Create a new label
g   create a new empty GPT partition table
G   create a new empty SGI (IRIX) partition table
o   create a new empty DOS partition table
s   create a new empty Sun partition table

Command (m for help): p
Disk /dev/loop0: 97.7 MiB, 102400000 bytes, 200000 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xd1d1a072

Command (m for help): n
Partition type
   p   primary (0 primary, 0 extended, 4 free)
   e   extended (container for logical partitions)
Select (default p): p
Partition number (1-4, default 1): 
First sector (2048-199999, default 2048): 
Last sector, +sectors or +size{K,M,G,T,P} (2048-199999, default 199999): +10M

Created a new partition 1 of type 'Linux' and of size 10 MiB.

Command (m for help): p
Disk /dev/loop0: 97.7 MiB, 102400000 bytes, 200000 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xd1d1a072

Device       Boot Start   End Sectors Size Id Type
/dev/loop0p1       2048 22527   20480  10M 83 Linux

Command (m for help): n
Partition type
   p   primary (1 primary, 0 extended, 3 free)
   e   extended (container for logical partitions)
Select (default p): p
Partition number (2-4, default 2): 
First sector (22528-199999, default 22528): 
Last sector, +sectors or +size{K,M,G,T,P} (22528-199999, default 199999): +20M    

Created a new partition 2 of type 'Linux' and of size 20 MiB.

Command (m for help): p
Disk /dev/loop0: 97.7 MiB, 102400000 bytes, 200000 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xd1d1a072

Device       Boot Start   End Sectors Size Id Type
/dev/loop0p1       2048 22527   20480  10M 83 Linux
/dev/loop0p2      22528 63487   40960  20M 83 Linux

Command (m for help): w
The partition table has been altered.
Calling ioctl() to re-read partition table.
Re-reading the partition table failed.: Invalid argument

The kernel still uses the old table. The new table will be used at the next reboot or after you run partprobe(8) or kpartx(8).

root@raspbeeerry:~# fdisk /dev/loop0 

Welcome to fdisk (util-linux 2.29.2).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.


Command (m for help): p
Disk /dev/loop0: 97.7 MiB, 102400000 bytes, 200000 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xd1d1a072

Device       Boot Start   End Sectors Size Id Type
/dev/loop0p1       2048 22527   20480  10M 83 Linux
/dev/loop0p2      22528 63487   40960  20M 83 Linux

Command (m for help): n
Partition type
   p   primary (2 primary, 0 extended, 2 free)
   e   extended (container for logical partitions)
Select (default p): e
Partition number (3,4, default 3): 
First sector (63488-199999, default 63488): 
Last sector, +sectors or +size{K,M,G,T,P} (63488-199999, default 199999): 

Created a new partition 3 of type 'Extended' and of size 66.7 MiB.

Command (m for help): p
Disk /dev/loop0: 97.7 MiB, 102400000 bytes, 200000 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xd1d1a072

Device       Boot Start    End Sectors  Size Id Type
/dev/loop0p1       2048  22527   20480   10M 83 Linux
/dev/loop0p2      22528  63487   40960   20M 83 Linux
/dev/loop0p3      63488 199999  136512 66.7M  5 Extended

Command (m for help): n
All space for primary partitions is in use.
Adding logical partition 5
First sector (65536-199999, default 65536): 
Last sector, +sectors or +size{K,M,G,T,P} (65536-199999, default 199999): +30M

Created a new partition 5 of type 'Linux' and of size 30 MiB.

Command (m for help): p
Disk /dev/loop0: 97.7 MiB, 102400000 bytes, 200000 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xd1d1a072

Device       Boot Start    End Sectors  Size Id Type
/dev/loop0p1       2048  22527   20480   10M 83 Linux
/dev/loop0p2      22528  63487   40960   20M 83 Linux
/dev/loop0p3      63488 199999  136512 66.7M  5 Extended
/dev/loop0p5      65536 126975   61440   30M 83 Linux

Command (m for help): w
The partition table has been altered.
Calling ioctl() to re-read partition table.
Re-reading the partition table failed.: Invalid argument

The kernel still uses the old table. The new table will be used at the next reboot or after you run partprobe(8) or kpartx(8).

root@raspbeeerry:~# fdisk -l
Disk /dev/sda: 149.1 GiB, 160041885696 bytes, 312581808 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x6484e662

Device     Boot     Start       End   Sectors   Size Id Type
/dev/sda1  *         2048 310501375 310499328 148.1G 83 Linux
/dev/sda2       310503422 312580095   2076674  1014M  5 Extended
/dev/sda5       310503424 312580095   2076672  1014M 82 Linux swap / Solaris


Disk /dev/loop0: 97.7 MiB, 102400000 bytes, 200000 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xd1d1a072

Device       Boot Start    End Sectors  Size Id Type
/dev/loop0p1       2048  22527   20480   10M 83 Linux
/dev/loop0p2      22528  63487   40960   20M 83 Linux
/dev/loop0p3      63488 199999  136512 66.7M  5 Extended
/dev/loop0p5      65536 126975   61440   30M 83 Linux
root@raspbeeerry:~# free
          total        used        free      shared  buff/cache   available
Mem:        1020528      100940      352364       27400      567224      753912
Swap:       1140728           0     1140728
root@raspbeeerry:~# fdisk -l
Disk /dev/sda: 149.1 GiB, 160041885696 bytes, 312581808 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x6484e662

Device     Boot     Start       End   Sectors   Size Id Type
/dev/sda1  *         2048 310501375 310499328 148.1G 83 Linux
/dev/sda2       310503422 312580095   2076674  1014M  5 Extended
/dev/sda5       310503424 312580095   2076672  1014M 82 Linux swap / Solaris


Disk /dev/loop0: 97.7 MiB, 102400000 bytes, 200000 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xd1d1a072

Device       Boot Start    End Sectors  Size Id Type
/dev/loop0p1       2048  22527   20480   10M 83 Linux
/dev/loop0p2      22528  63487   40960   20M 83 Linux
/dev/loop0p3      63488 199999  136512 66.7M  5 Extended
/dev/loop0p5      65536 126975   61440   30M 83 Linux

todo : see GNU parted that is a most advanced partition editor

Linux FS

• ext
• ext2: no journal: for small spaces
• ext3: journal
• ext4: last version of ext FS
• reiserfs
• jfs
• xfs

FS from others OS

• FAT: legacy from dos/windows 95. file size limited to 4GO. works well with linux, mac, windws
• NTFS: from windows 2000
• HFS: hierarchical FS

• create a file of the partition size with dd command
• associate it to a loop device with losetup command
• partition it with fdisk

dd command

utility to copy files/partition create a file named my-hd-file

Create a 100Mo file filed with 0 from /dev/zero:

touch my-hd-file
dd if=/dev/zero of=my-hd-file bs=1024000 count=1
1+0 records in
1+0 records out
1024000 bytes (1.0 MB, 1000 KiB) copied, 0.0318375 s, 32.2 MB/s
root@raspbeeerry:~# dd if=/dev/zero of=my-hd-file bs=1024000 count=100
100+0 records in
100+0 records out
102400000 bytes (102 MB, 98 MiB) copied, 0.749057 s, 137 MB/s

Loop device

In Unix-like operating systems, a loop device, vnd (vnode disk), or lofi (loop file interface) is a pseudo-device that makes a file accessible as a block device.

• losetup -f to identify next available loop device number => /dev/loop0

• losetup -a: list all loop devices

  root@raspbeeerry:~# losetup -a root@raspbeeerry:~# losetup -f /dev/loop0 root@raspbeeerry:~# losetup /dev/loop0 my-hd-file root@raspbeeerry:~# losetup -a /dev/loop0: [2049]:2752537 (/root/my-hd-file) root@raspbeeerry:~#