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16 Cards in this Set
- Front
- Back
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Why is it easy to manipulate most devices on a Unix system?
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Because the kernel presents many of the device I/O interfaces to user processes as files. These device files are sometimes called device nodes.
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What directory are device files stored in?
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/dev
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What characters in the read bits denote if a file is a device?
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b c p s block, character, pipe, socket
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How is a block device used?
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Programs access data from a block device in fiexed chunks. A block device's total size is fixed and easy to index, so processes have random access to any block in the device with the help of the kernel.
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What are sockets?
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Special-purpose interfaces that are frequently used for interprocess communication.
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What is the function of the program dd?
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To read from an input file or stream and write to an output file or stream, possibly doing some encoding conversion on the way.
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What is an example of dd syntax?
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dd if=/dev/zero of=new_file bs=1024 count=1
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What is the dd option format based on and how is it different than other option formats of Unix commands?
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It is based on IBM Job Control Language (JCL) and rather than using a dash to signal an option you name an option and set its value to something with the equals sign.
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dd if
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input file (default is stdin)
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dd of
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output file (default is stout)
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dd bs
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block size in bytes (can also do kilobytes, or 1024 bytes)
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dd ibs=size, obs=size
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input and output block sizes
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dd count=num
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The total number of blocks to copy.
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Why is it important to add a stopping point for dd with count?
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When working with a huge file, or with a device that supplies an endless stream of data, such as /dev/zero, you want dd to stop at a fixed point or you could waste a lot of disk space, CPU time, or both.
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dd skip=num
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skip past the first num blocks in the input file or stream adn do not copy them to the output
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What is the command to see the block and character devices for which your system currently has drivers?
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cat /proc/devices
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