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larry
Asked: 2011-01-17 22:42:04 +0800 CST

One shell question with ssh

  • 772

I find one shell command can send large data to target host:

dd if=/dev/zero bs=4096 count=1048576 | ssh user@ip 'cat > /dev/null'

I think i can use this to test network bandwidth, but it can not display the process status.

ssh shell

5 Answers

  1. Best Answer

    Well if you wrap this whole thing in time:

    time sh -c "dd if=/dev/zero bs=4096 count=1048576 | ssh user@ip 'cat > /dev/null'"

    that will give give you the time it takes the transfer to complete. Divide the bytes transferred by the time and that's your throughput.

    For a progress meter, you can use pv, which eliminates the need to use time(1):

    dd if=/dev/zero bs=1024 count=10000 | pv --size 10240000 | ssh user@ip 'cat > /dev/null'

    which will give you a nice progress meter, especially if you load the --size argument with the total size of the transfer.

    • 9

  2. If what you want to do is test network bandwidth, there are more direct ways of doing so.

    Try out ttcp or its replacement: nuttcp

    [tla ~]$ nuttcp -S

michael@challenger:~$ nuttcp -4 -r tla
   41.5574 MB /  10.46 sec =   33.3336 Mbps 2 %TX 4 %RX
michael@challenger:~$ nuttcp -4 -t tla
   15.4347 MB /  10.13 sec =   12.7821 Mbps 1 %TX 2 %RX 0 retrans 3.30 msRTT
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  3. Sending SIGUSR1 to dd will cause it to output its progress. You could calculate the difference between subsequent invocations in order to get an approximate rate.

    • 2

  4. you can use iperf if you really want to test connectivity with great detail.

    Otherwise,

    Create a 100mb test file

    dd if=/dev/urandom of=./test.bin bs=1024000 count=100

    then scp this file to test upload performance

    scp test.bin x.x.x.x:.

    or scp from the far side to test your download performance

    • 1

  5. Usually better to use iperf to test bandwidth, beacuse it has no encryption overhead, but you can insert pv between dd and ssh to see transfer speed in real-time:

    dd if=/dev/random | pv | ssh somehost 'cat > /dev/null'

    Also, on FreeBSD you can send SIGINFO to dd by hitting Ctrl+T, after that some stats (including speed) will be displayed

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