How do I know if dd is still working?

Question

I've not used dd all that much, but so far it's not failed me yet. Right now, I've had a dd going for over 12 hours - I'm writing an image back to the disk it came from - and I'm getting a little worried, as I was able to dd from the disk to the image in about 7 hours.

I'm running OSX 10.6.6 on a MacBook with a Core 2 Duo at 2.1ghz/core with 4gb RAM. I'm reading from a .dmg on a 7200rpm hard drive (the boot drive), and I'm writing to a 7200rpm drive connected over a SATA-to-USB connector. I left the blocksize at default, and the image is about 160gb.

EDIT: And, after 14 hours of pure stress, the dd worked perfectly after all. Next time, though, I'm going to run it through pv and track it with strace. Thanks to everyone for all your help.

Answer 1

You can send dd a certain signal using the kill command to make it output its current status. The signal is INFO on BSD systems (including OSX) and USR1 on Linux. In your case:

kill -INFO $PID

You can find the process id ($PID above) with the ps command; or see pgrep and pkill alternatives on mac os x for more convenient methods.

More simply, as AntoineG points out in his answer, you can type ctrl-T at the shell running dd to send it the INFO signal.

As an example on Linux, you could make all active dd processes output status like this:

pkill -USR1 -x dd

After outputting its status, dd will continue coping.

Answer 2

Under OS X (didn't try on Linux), you can simply type Ctrl+T in the terminal running dd. It will print the same output as kill -INFO $PID, plus the CPU usage:

load: 1.40  cmd: dd 34536 uninterruptible 3.49u 64.58s
5020305+0 records in
5020304+0 records out
2570395648 bytes transferred in 4284.349974 secs (599950 bytes/sec)

I found out about it reading this thread, and trying to open a new tab in my terminal but mixing ⌘+T with Ctrl+T.

Answer 3

For dd, you can send a signal. For other commands that are reading or writing to a file, you can watch their position in the file with lsof.

lsof -o -p1234    # where 1234 is the process ID of the command
lsof -o /path/to/file

If you plan in advance, pipe the data through pv.

Answer 4

A more general way is to use iotop that displays the current amount of disk reading / writing per program.

EDIT: iotop -o show only programs which perform currently I/O operations (thanks Jason C for this comment).

Answer 5

As of coreutils v8.24, dd has native support for showing progress. Just add the option status=progress.

Example:

dd if=arch.iso of=/dev/sdb bs=4M status=progress

Source

Answer 6

I usually attach strace to such a running process (with the -p $PID option) to see if it stays blocked in a system call or if it is still active.

Or, if you feel nervous about sending a signal to the running dd, start another dd to validate if this works.

Answer 7

For next time, you can just use pv from the start (if it's available through your package manager, install it). This is a utility with the sole purpose of piping input to output and monitoring progress and speed.

Then, for writing an image to a drive, say with 4MB block size:

pv -ptearb /path/to/image.bin | dd iflag=fullblock of=/dev/whatever bs=4M

Aside from initial buffering (offset by a final sync, which can be done through dd if you want), this will show you a progress bar, average speed, current speed, and ETA.

The iflag=fullblock option forces dd to grab full blocks of input through pv, otherwise you're at the mercy of the pipe for block sizes.

To go the other way use dd to read and pv to write, although you have to explicitly specify the size if the source is a block device. For a 4GB device:

dd if=/dev/whatever bs=4M | pv -ptearb -s 4096m > /path/to/image.bin

You could also determine the size automatically, something like:

dd if=/dev/whatever bs=4M | pv -ptearb -s `blockdev --getsize64 /dev/whatever` > /path/to/image.bin

It really doesn't matter what order you do dd and pv in, it's entirely performance-related -- if the device you are reading to or from has optimal performance for certain blocksizes you want to use dd instead of pv to access that device. You can even stick a dd on both ends if you want, or not at all if you don't care:

pv -ptearb /path/to/image.bin > /dev/whatever
sync

Answer 8

ddrescue will give you stats as it's running.

demo: http://www.youtube.com/watch?v=vqq9A01geeA#t=144s

Answer 9

Sometimes you may not be able to use the INFO or USR1 signal because the stderr stream of the dd process is not accessible (e.g. because the terminal in which it was executed was already closed). In this case, a workaround is to do the following (tested on FreeBSD, may be slightly different on Linux):

1. Use iostat to estimate the average write rate (MB/s) to the target device, e.g.:

   iostat -d -w30 ada0

   Substitute your target device name for ada0 here, and wait a minute for it to give a couple results. The "w" parameter determines how many seconds between samples. Increasing it will give a better average estimate with less variance, but you'll have to wait longer.

2. Use ps to determine how long dd has been running:

   ps -xo etime,command | grep dd

   Convert this to seconds to get total seconds of runtime.

3. Multiply total seconds of runtime by average write rate to get total transferred MB.

4. Get the device size in MB with:

   grep ada0 /var/run/dmesg.boot

   Substitute your target device name for ada0. Divide the result by the average write rate to get the total transfer time in seconds. Subtract the time it's been running so far to get time remaining.

This strategy only works if dd has been writing continuously at the current average write rate since it began. If other processes are competing for the CPU or I/O resources (including the I/O bus) then it may reduce the transfer rate.

Answer 10

I started using dcfldd(1), which shows dd operations in a better way.

Answer 11

You can use progress which, in particular, shows the progress of a running dd. It uses /proc/$pid/fd and /proc/$pid/fdinfo which you can also monitor by hand.

Answer 12

While dd is executing, run this in another terminal as root:

while pgrep ^dd; do pkill -INFO dd; sleep 1; done

It prints the dd status every 1 second in the original terminal window where dd is executing, and quits when the command is done.

Answer 13

The wchar line (written characters) in /proc/$pid/io can give you precise information about the dd process. As long as it changes, your dd is still working!

Here is a neat little php script, which you can save and then execute with php filename.php during the dd to display the written bytes. The nice benefit of watching /proc/$pid/io over kill -USR1 $(pidof dd) is that you do not have to switch between terminals, which is not always an option.

<?php

/** Time between refreshs in seconds */
$refresh = 1;


/**
 * Start of Script 
 */

if (!($pid = exec('pidof dd')))
    exit("no dd running\n");

$history = array();
$break_ms = $refresh * 1000000;
$start_time = exec("ls -ld /proc/$pid --time-style=+\"%s\" | egrep -o [0-9]{10}");


fprintf(STDOUT, "PID: %s\n", $pid);
fprintf(STDOUT, "START TIME: %s\n\n", date("Y-m-d H:i:s", $start_time));


while (true) {
    if (isset($curr))
        array_push($history, $curr);

    if (count($history) > 10) array_shift($history);
    $oldest = reset($history);
    $latest = end($history);

    /**
     * get number of written bytes from /proc/$pid/io
     */
    #if (!($curr = exec("cat /proc/$pid/io | grep ^write_bytes | sed 's/write_bytes: //g'")))
    #    break;

    /* prepare proc_open() parameter */
    $descriptorspec = array(
        0 => array('pipe', 'r'), // stdin
        1 => array('pipe', 'w'), // stdout
        2 => array('pipe', 'w'), // stderr
    );

    $process = proc_open("cat /proc/$pid/io | grep ^write_bytes | sed 's/write_bytes: //g'", $descriptorspec, $pipes);
    if (!is_resource($process)) break;

    $stdout = stream_get_contents($pipes[1]);
    $stderr = stream_get_contents($pipes[2]);
    proc_close($process);

    if (!empty($stderr)) break;
    $curr = trim($stdout);

    /**
     * caculate elapsed time from start */
    $time_elapsed = time() - $start_time;

    /**
     * avg speed since start */
    $avg = $time_elapsed > 0 ? round($curr / $time_elapsed) : 0;

    /**
     * avg speed of last 10 updates */
    if (count($history) > 0)
        $speed = human_file_size(round(($latest - $oldest) / count($history) / $refresh));

    $output = sprintf("\rBYTES WRITTEN: %s [%s]  ::  CURRENT: %s/s  ::  AVERAGE: %s/s  ::  ELAPSED: %s", $curr, human_file_size($curr), isset($speed) ? $speed : 0, human_file_size($avg), gmdate("H:i:s", $time_elapsed));
    printf("%s%s", $output, str_repeat(" ", exec("tput cols") - strlen($output)));

    usleep($break_ms);
}

fprintf(STDOUT, "\ndd has finished!\n\n");

function human_file_size($size,$unit="") {
  if( (!$unit && $size >= 1<<30) || $unit == "GB")
    return number_format($size/(1<<30),2)." GB";
  if( (!$unit && $size >= 1<<20) || $unit == "MB")
    return number_format($size/(1<<20),2)." MB";
  if( (!$unit && $size >= 1<<10) || $unit == "kB")
    return number_format($size/(1<<10),2)." kB";
  return number_format($size)." bytes";
}

Answer 14

If you write to a slow drive, for example a USB drive, you may want to know not only the progress of the command dd itself, but also the progress of actual writing to the target device.

• One way way know when the process has finished is to run sync after the dd command and wait for it to finish flushing the buffers, so that the terminal window returns to prompt. But there is still no display of progress. You can monitor the progress of flushing by watching the 'dirty' data for example with the shellscript watch-flush, that is part of mkusb. This shell-script uses data from the system file /proc/meminfo.

• It is more straightforward to modify the dd command line to make it flush the buffers regularly, for example after writing each mibibyte, and at the same time show the progress, for example

  sudo dd if=file.img bs=1M of=/dev/sdx status=progress oflag=dsync
  

  Please check and double-check, that you specify the correct target device. Otherwise you might overwrite valuable data. dd does what you tell it to do without any questions, and for this reason it has earned the nickname 'Data Destroyer'.

• In Ubuntu and Debian you can also use mkusb to perform the cloning task. It will wrap a safety belt around dd: help you identify the target device and let you double-check it before you launch the process.