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So I ran the following command in Cygwin: dd if=/dev/zero of=E:
Now my C: drive lost all its free space. Upon unpluggin my E: drive from its USB port, the PC automatically shuts down. Is /dev/zero being created within the C: drive, and if so does that make it potentially unsafe to use with Cygwin?
Writing directly to disks is really DANGEROUS on any system
On cygwin the disks as physical entities are not the windows letter E: or the logical /cygdrive/e entities
If you want to completely overwrite the physical structure
dd if=/dev/zero of=/dev/sdXX
Pay REALLY attention to your final destination, or you will
BLOW your system.
/dev/sda full first disk
/dev/sda1 first disk, first partition
/dev/sdb full second disk
/dev/sdb1 second disk, first partition
and so on...
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I've seen that df -H --total gives me the total space available but only of mounted devices, and lsblk gives me the sizes of all storage devices, yet not how much space is available within them.
Is there a way I could see the sum total, available storage space of all devices, e.g. hard disks, thumb drives, etc., in one number?
The operation of mounting a medium makes the operating system analyze the file system.
Before a medium is mounted, it exists as a block device and the only fact the OS might know about it might be the capacity.
Other than that, it is just a stream of bytes not interpreted in any way. That "stream of bytes" very probably contains the information of used and unused blocks. But, dependent on file system types, in very different places and can thus not be known by the OS (other than mounting and analyzing it)
You could write a specific application that would extract that information, but I would consider that temporarily mounting the file system. Standard Unix/Linux doesn't come with such an application.
From the df man page, I'd say "No", but the wording indicates that it may be possible on some sytems/distributions with some version(s) of df.
The other problem is how things can be accessed. For example, the system I'm using right now shows 3 160gb disks in it... but df will show one of them at / and the other 2 as a software based RAID-1 setup on /home.
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I have a problem using dd command, assume that I am writing 20MB file to 100MB partition. After the write I am not able to access the rest of 80MB.
dd if=temp_file of=/dev/sdb1
Is there a way I can specify dd to adjust to the file system that I am writing into?
All I am interested is know if there is a way to use the 80MB space without disturbing the initial 20MB.
By using the dd command the way you do, you overwrite the file-system data, including the important meta-data about the file-system. If the temp_file contains a file-system for a 20MB partition then that's what you will get.
If you want a 100MB partition, you need to create a 100MB disk-image to write to the disk.
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I have run bitbake core-image-minimal-dev properly configured for a genericx86 machine. BitBake generates a bootia32.efi, a bzImage--<stuff>.bin, an .hddimg, an .iso, a .rootfs.ext3, a .rootfs.ext4, a .rootfs.tar.bz2, and a core-image-initramfs-<stuff>.rootfs.cpio.gz. I'm interested in a method of how to dd one or more of these onto the hard disk of my target machine and boot from that hard disk.
dd if=path/to/imagefile/imagename.hddimg of=/dev/usbdevicename
You'll find the correct usb device name e.g. by plugging in the usb disk and looking at dmesg|tail output -- do not guess as mistakes will be fatal to your hard disk. A practical example from my build machine:
sudo dd if=tmp/deploy/images/intel-corei7-64/core-image-sato-intel-corei7-64.hddimg \
of=/dev/sdb \
bs=4096
Note that you probably want to use intel-corei7-64 as the machine unless you know that genericx86 is correct for your hardware: despite the name former is the common Intel BSP for anything that's not ancient (that includes big Cores, Xeons, Atoms ...).
How to boot the image depends on your target device: you may need to go to BIOS settings to select "boot from USB".
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I'm running shred against blockdevice with couple of etx4 filesystems on it.
The blockdevices are virtual drives - RAID-1 and RAID-5. Controller is PERC H710P.
command
shred -v /dev/sda; shred -v /dev/sdc ...
I can understand from shred man(info) page that shred might be no effective on journal filesystems but only when shredding files.
Anyone can please explain whether is shredding against blockdevice safe way to destruct all data on it?
This is a complex issue.
The only way that is 100% effective is physical destruction. The problem is that the drive firmware can mark sectors as bad and remap them to a pool of spares. These sectors are effectively no longer accessible to you but the old data may be recoverable from those sectors by other means (such as an alternate firmware or physically removing the platters).
That being said, running shred on the block device does not have the issues due to journaling.
The problem with journaling is that for partial overwrites to be recoverable you cannot actually overwrite the original data, so the overwrite of the file takes place in a second physical location, leaving the first in tact. Writing directly to the block device is not subject to journaling.
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I am asking this question after searching a lot on Internet.
I am using linux on my PC. It has a disk which has 3 partitions. sda1, sda2, sda3. sda3 contains linux, sda2 is swap and sda1 is FAT.
My question is that "sda3" is a partition which contains whole when linux than I don't understand what do you mean by mounting it on /dev/sda3?
/home, /usr, /var everything is inside sda3 then why are we saying that we are mounting sda3 on /dev while /dev and all the other filesystems are in sda3?
/dev is a directory containing ''pointers'' (in the form of block/character special files) that give the user/programs access to special devices that only the kernel has access to normally.
sda3 isn't actually mounted on /dev/sda3, that's just the block special file that lets us manipulate sda3. The real ''mount point'' is /.
I found my answer after reading http://en.wikipedia.org/wiki/Device_file
/dev/sda3 is actually a device file.