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The above command will send 4GB of data from one host to the next over the network, without consuming any unnecessary disk on either the client nor the host. This is a quick and dirty way to benchmark network speed without wasting any time or disk space.
Of course, change the byte size and count as necessary.
This command also doesn't rely on any extra 3rd party utilities, as dd, ssh, cat, /dev/zero and /dev/null are installed on all major Unix-like operating systems.
dcfldd is a forensic version of dd that shows a process indicator by default.
The 'dd' command doesn't provide a progress when writing data. So, sending the "USR1" signal to the process will spit out its progress as it writes data. This command is superior to others on the site, as it doesn't require you to previously know the PID of the dd command.
"killall -USR1 dd" does not work in OS X for me. However, sending INFO instead of USR1 works.
every 1sec sends DD the USR1 signal which causes DD to print its progress.
This line removes the 300k header from a Nero image file converting it to ISO format
bs = buffer size (basically defined the size of a "unit" used by count and skip)
count = the number of buffers to copy (16m * 32 = 1/2 gig)
skip = (32 * 2) we are grabbing piece 3...which means 2 have already been written so skip (2 * count)
i will edit this later if i can to make this all more understandable
Requires the dc3dd package - available at http://dc3dd.sourceforge.net
This is a more accurate way to watch the progress of a dd process. The $DDPID=$! is needed so that you don't get the PID of the sleep. The sleep 1 is needed because in my testing at least, if you run kill -USR1 against dd too quickly, it will kill it off instead of display the status. So you need to wait a second, probably so that it can configure itself to trap the USR1 signal.
If you have some drive imaging to do, you can boot into any liveCD and use a commodity machine. The drives will be written in parallel.
To improve efficiency, specify a larger block size in dd:
dd if=/dev/sda bs=64k | tee >(dd of=/dev/sdb bs=64k) | dd of=/dev/sdc bs=64k
To image more drives , insert them as additional arguments to tee:
dd if=/dev/sda | tee >(dd of=/dev/sdb) >(dd of=/dev/sdc) >(dd of=/dev/sdd) | dd of=/dev/sde
This is similar to how you would generate a file with all zeros
dd if=/dev/zero of=allzeros bs=1024 count=2k
Put into some file. No special purpouse, just for fun...
For disk space constraint testing. Leaves a little space available for creating temp files, etc. Easily free up the used disk space again by deleting the dummy00 file. Can tailor the testing by building smaller 'blocks' to suit the needs of the testing.
WARNING: do not do this to the '/' (root) filesystem unless you know what you are doing... on some systems it could crash the OS.
This is an useful command for when your OS is reporting less free RAM than it actually has. In case terminated processes did not free their variables correctly, the previously allocated RAM might make a bit sluggis over time.
This command then creates a huge file made out of zeroes and then removes it, thus freeing the amount of memory occupied by the file in the RAM.
In this example, the sequence will free up to 1GB(1M * 1K) of unused RAM. This will not free memory which is genuinely being used by active processes.
A dear friend of mine asked me how do I copy a DVD to your hard drive? If you want to make a copy of the ISO image that was burned to a CD or DVD, insert that medium into your CD/DVD drive and (assuming /dev/cdrom is associated with your computer?s CD drive) type the following command
This command clone the first partition of the primary master IDE drive to the second partition
of the primary slave IDE drive (!!! back up all data before trying anything like this !!!)
Create a bunch of random files with random binary content. Basically dd dumps randomly from your hard disk to files random-file*.
This will create a 10 MB file named testfile.txt. Change the count parameter to change the size of the file.
As one commenter pointed out, yes /dev/random can be used, but the content doesn't matter if you just need a file of a specific size for testing purposes, which is why I used /dev/zero. The file size is what matters, not the content. It's 10 MB either way. "Random" just referred to "any file - content not specific"