Schedule Tasks Using Crontab on Windows 10 with WSL

Notes ,

Update (12/30/2019): This was originally written on 09/25/2018 and was for WSL 1. At the time of writing this line, the setup for my WSL 1 still works (with win10 1909).

This is a short tutorial about how to use WSL(Windows Subsystem for Linux) to schedule cron jobs, with a specific example of backing up Evernote’s database, to show how versatile this method is and potential benefits. In this example, the strategy is optimized for large files that have frequent small changes regarding I/O writes.

Jump directly to procedure

Motivation

It was the second time for me to lose a note in Evernote. The first one was due to a sync error. It was nothing serious but unnerving. But I lost the second one merely after I locked my phone while being prompted to type the password for some encrypted text in that note. And the problem is, I have almost no direct way to know if a note is missing considering the size of my Evernote database.

So, after searching around, I decided that, since Evernote is still the best app for my note taking (it has unlimited cloud storage, support for most platforms, bots for different apps etc.) and there is no 100% secure data storage in this world, I need to backup the database file on my own.

Side note: I saw a lot of discussion about switching applications to have more secure database. Unfortunately, that is not the case. Evernote is mature enough that the official client gives users the option to backup the database directly and access with ease later on. To prevent data loss, the ultimate solution is to have multiple backups.

Why rsync and WSL

It is tedious to manually copy and paste the database files to other locations (and track the version history). Storing the db directly inside the local cloud storage sync folder is also not feasible for me since those applications need to scan my 3.14 GB .exb file each time when I make any tiny changes to my notes.

I need a scheduled job with minimum disk usage (reading and writing). The reading part is hard to get rid of. So the focus is I/O write usage. I need a binary incremental backup. rsync is the best candidate I know so far but it does not have native support for Windows.

My Solution

Since I need my cloud storage application to run in the background all the time, it is not viable for me to schedule that application to sync. The workaround is to use scheduled rsync to copy the .exb file to the local sync folder.

rsync is able to do binary incremental copy, keeping the write usage at minimum. And the sync application only reads the local file as scheduled (my specific application, Dropbox, can binary incremental sync, too). Unless there is a way to directly binary incremental copy to the cloud as scheduled while the other parts are not affected, this solution only needs 2 full scans and very little write + upload to work.

(I know rclone but it does not support binary incremental upload)

Procedure

About the Database File

There is an official guide for it. It explains how to find the location, how to export the note from a database file and so on.

Preparation

If not installed yet, install cloud storage sync clients, WSL for Windows, cron and rsync based on the Linux distro installed.

Decide the rsync Command

To learn more about cron, use man cron and man crontab or search online.

Please at least read the rsync --help and decide which options are preferred. The following command is the one I am using.

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rsync -u -t -av -n /mnt/c/Evernote/Databases/myName.exb /mnt/c/Dropbox/EvernoteDB/myName.exb

The -n flag enables dry-run. Remove it after everything is confirmed to be correct by running this command directly (and see the result).

Create crontab Job

Log in as the user you want to run the job (note the privileges) and edit their crontab:

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crontab -e

Using the editor chosen, add this line:

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22 22 */2 * * rsync -u -t -av /mnt/c/Evernote/Databases/myName.exb /mnt/c/Dropbox/EvernoteDB/myName.exb > /dev/null

This is my config. It will run the command every 2 days at 22:22 (10:22 pm) and thus backup my Evernote database every 2 days.

If you want to learn more about crontab job, feel free to search on your own.

If you want, you can use the snapshot feature of rsync. But since Dropbox has pretty good version history, I did not include that.

(Since a note might be found missing after a long time, I highly recommend manually adding backups for longer period, Like a full backup for each half year using another cron job)

Make the Daemon start at Windows Boot

The last step is to make sure the cron daemon runs in background when Windows boots. It can be achieved by making bash.exe/wsl.exe a service and so on.

The solution I chose was to create a shortcut containing a start command in the shell:startup folder. Feel free to have your own choices and search around.

First, make sure the start command can be run without root privilege, unless you want to type in your sudo password every time you boot Windows.

Open sudo config file:

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sudo visudo

Add the following line:

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%sudo ALL=NOPASSWD: /etc/init.d/cron start

Save and quit and fix any problem if prompted.

Next, type shell:startup in the Run and explorer will open the startup folder.

Create a shortcut to wsl.exe and edit the properties as following:

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C:\Windows\System32\wsl.exe sudo /etc/init.d/cron start

And it should work unless the developers change how wsl works in the future.

Check If cron Service Started Properly

If you are worrying about cron service, here is a way to test it.

Create a test job in crontab. For example:

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35 * * * * echo "test" >> /home/MY_USER/test

It will append “test” to a file in that path for every hour at 35.

First wait for the job to run first time and check the file to see result.

Now manually terminate the cron service and reboot Windows to see if it works.

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wsl sudo /etc/init.d/cron stop

After reboot, check task manager to see if there is a process called cron running.

Wait for the to run second time and check the result.

The command above is only an example. You can change it however you like.

Conclusion

Until now, it should be clear that what I did is only a little trick. But it shows how Unix commands can make Windows easier to use with WSL.

Reference

Updates

  • 11/16/2018: changed the original title and added abstract summary