Intro To 'sync' Command In Linux
2023-06-05 - By Robert Elder
I use the 'sync' command to ensure that any cached writes are committed to persistent storage:
sync
Here, I have an important piece of data that I want to back up to an external hard drive:
![Using 'cp' Command](https://blog.robertelder.org/intro-to-sync-command/using-cp-command_600x600_q60_s26137.jpeg)
I use the 'cp' command to copy this data onto the external hard drive:
cp my-important-data.zip /external-drive/my-important-data.zip
As the 'cp' command runs, I no longer have control over the command prompt, but I can see that the destination file size is growing larger:
![Lost Control Over Prompt](https://blog.robertelder.org/intro-to-sync-command/lost-control-command-prompt_600x600_q60_s30335.jpeg)
Eventually, the command prompt comes back and the destination file size stops increasing. 13 seconds later, I decide to unplug my external hard drive believing that the data has finished copying:
![Unplugging External Drive](https://blog.robertelder.org/intro-to-sync-command/unplugging-external-drive_600x600_q60_s18415.jpeg)
When I plug the drive back in, the file size is now smaller and the checksum doesn't match, indicating that the backup is corrupt:
![Data Is Now Corrupt](https://blog.robertelder.org/intro-to-sync-command/data-is-now-corrupt_600x600_q60_s24099.jpeg)
That's why I always use the 'sync' command even if the drive activity light has stopped flashing:
sync
After using the 'sync' command, the data will finish copying for a few seconds, and then return control to the prompt. Now, the file sizes are correct and the checksums match!
And that's why the 'sync' command is my favourite Linux command.
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