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How To Make the dd Command Wait for Full Disk Write in Bash

Ubuntu 7

In Bash, there are several commands that you can use to interact with your system’s disks. One of the most powerful and versatile is the dd command. However, by default, dd does not wait for the entire disk write operation to complete before returning control to the user. In this article, we will discuss how to make the dd command wait for the full disk write operation to finish.

Quick Answer

To make the dd command wait for full disk write in Bash, you can either use the conv=fdatasync option or use the sync command after running dd. Alternatively, you can use tee as a safer and potentially faster option.

Understanding the dd Command

Before we delve into the specifics, it’s important to understand what the dd command does. The dd command is a Unix utility that converts and copies files. The if parameter stands for “input file”, the of parameter stands for “output file”, and the bs parameter stands for “block size”. Here is a basic usage of the dd command:

sudo dd if=~/Desktop/ubuntu.iso of=/dev/sdx bs=1M

In this example, dd is copying the content of ubuntu.iso from the Desktop to a disk (/dev/sdx), with a block size of 1M.

Making dd Wait for Disk Write Completion

To make dd wait for the copying process to finish, you can use the conv=fdatasync option. This option tells dd to use special options to ensure that the data is written to the physical device. Here’s how to use it:

sudo dd if=~/Desktop/ubuntu.iso of=/dev/sdx conv=fdatasync bs=1M

The conv=fdatasync option ensures that the data is fully written to the disk before the command returns control to the user.

Using the sync Command

An alternative method is to use the sync command after running dd. The sync command flushes the file system buffers to the disk(s), ensuring that all pending write operations are completed. Here’s how to use it:

sudo dd if=~/Desktop/ubuntu.iso of=/dev/sdx bs=1M; sync

When the sync command returns, you can be sure that the data has been fully written.

Using tee as an Alternative to dd

Instead of using dd, you can use tee as an alternative. This can be advantageous because there’s less risk of inverting the source and destination due to a typo, and it may be slightly faster:

<~/Desktop/ubuntu.iso sudo tee /dev/sdx >/dev/null; sync

In this command, tee reads from standard input and writes to standard output and files. The >/dev/null part discards the standard output, and sync ensures that all data is written to the disk.

Conclusion

In summary, to make dd wait for the full disk write operation to finish, you can use the conv=fdatasync option or use the sync command after running dd. Alternatively, you can use tee as a safer and potentially faster option. Remember to always handle disk operations with care to prevent data loss.

What is the purpose of the `dd` command?

The dd command is a Unix utility used for converting and copying files. It can also be used for disk cloning and low-level disk operations.

How do I make `dd` wait for the full disk write operation to finish?

You can make dd wait for the full disk write operation to finish by using the conv=fdatasync option or by using the sync command after running dd.

What does the `conv=fdatasync` option do?

The conv=fdatasync option tells dd to use special options to ensure that the data is fully written to the disk before returning control to the user.

How do I use the `sync` command after running `dd`?

To use the sync command after running dd, you can simply add ; sync to the end of the dd command. This will flush the file system buffers to the disk and ensure all pending write operations are completed.

Can I use `tee` as an alternative to `dd`?

Yes, you can use tee as an alternative to dd. It can be advantageous because there’s less risk of inverting the source and destination due to a typo, and it may be slightly faster.

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