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If you leave out the block size it defaults to 512 bytes. I set it to 16 Megabytes and it was much faster...
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.
See: http://imgur.com/JgjK2.png for example.
Do some serious benchmarking from the commandline. This will write to a file with the time it took to compress n bytes to the file (increasing by 1).
gnuplot -persist <(echo "plot 'lzma' with lines, 'gzip' with lines, 'bzip2' with lines")
To see it in graph form.
Intentional hash in the beginning. May run a looong time. Wipes your data for real. Was meant to be /dev/urandom - I mistyped it. :-)
You can use this to directly dump from machine A (with dvd drive) to machine B (without dvd drive) . I used this to copy dvd using my friend's machine to my netbook. Above command is to be issued on machine B.
1) No wasting time dumping first to machine A and then copying to Machine B.
2) You dont need to use space on Machine A. In fact, this will work even when Machine A doesnt have enough hdd space to dump the DVD.
Use -C ssh option on slow networks (enables compression).
you can replace "dd if=/dev/dvd" with any ripping command as long as it spews the iso to stdout.
Overwrites the boot sector. Since this doesn't overwrite any data, you can usually recover by re-creating the partition table exactly the same as before you zeroed it. This can also help sometimes if you install a new drive in a Windows machine which can't read it.
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*.
Same as above but slooooow it down
Let dd use direct I/O to write directly to the disk without any caching. You'll encounter very different results with different block sizes (try with 1k, 4k, 1M, ... and appropriate count values).
Note, the [remotePort] should be opened in the firewall first. First, start the destination box listening, then fire off the sending box. Data from the /dev/zero device in memory of the source machine is read out using dd, sent over the network with nc, and read back in from the other side of the network with nc, going to the /dev/null device. Essentially, it is a memory-network-memory copy operation, the output of dd will tell you how fast your network really is performing.
Depending on the speed of you system, amount of RAM, and amount of free disk space, you can find out practically how fast your disks really are. When it completes, take the number of MB copied, and divide by the line showing the "real" number of seconds. In the sample output, the cached value shows a write speed of 178MB/s, which is unrealistic, while the calculated value using the output and the number of seconds shows it to be more like 35MB/s, which is feasible.
Solves "tr" issues with non C-locales under BSD-like systems (like OS X)
This command securely erases all the unused blocks on a partition.
The unused blocks are the "free space" on the partition.
Some of these blocks will contain data from previously deleted files.
You might want to use this if you are given access to an old computer and you do not know its provenance.
The command could be used while booted from a LiveCD to clear freespace space on old HD.
On modern Linux LiveCDs, the "ntfs-3g" system provides ReadWrite access to NTFS partitions thus enabling this method to also be used on Wind'ohs drives.
NB depending on the size of the partition, this command could take a while to complete.