Synchronize two folders on Android with all subfolders and files in them?

The question is about synchronizing two folders residing in Android phone itself.
I've spent hours experimenting with no success.

Programs offer folder content sync but not syncing all sub folders and contents inside subfolders multiple layers deep.
Programs offer cloud and PC synchronization but what about simply two folders both inside the Android phone, with no internet or any other connection necessary?

The obvious goal being synchronizing removable SD Card folder content with internal SD card folder content.
I've tried Google Playstore search and I have a headache from hours of not being able to do a simple two folder sync using programs that claim they are sync programs - but they can't sync two folders with subfolders inside them.

What do you mean synch exactly please? Would you like to for instance create a shortcut on the desktop that contains both folders? Would you like app content to sync with cloud storage? I just can't think of any reason to sync those folders.... Perhaps APPS2SD might be what you are looking for? Also the answer might be android version dependent. After KK there were drastic changes in function of the operating system.

Sure. Let me clarify, and maybe you can help me figure out how to word it better because I will be asking this in the future, and I am more than a little surprised people don't have a need for this on Android:

I simply wish to make ALL contents of folder A be changed so that they are identical to folder B.
That to me is what the word synchronizing means.

This has nothing to do with shortcuts anywhere.
I absolutely do not need any cloud or PC interaction.
I have a rooted phone. Yes.
This has nothing to do with apps.

So synchronize folder A so that its contents are identical to folder B. 10/10 times, 100% of the time, the answers I get have to do with PCs and Clouds, whereas I only want to, sync two existing folders.

I am pretty sure it's not what you're looking for but I think the dd command may help.

dd if=source of =destination

will move a copy a file for you. Double the destination field

dd if=source of=destination of=destination

Should copy into multiple locations. Be careful with the dd command however. It has a nickname.... Data destroyer. Apparently unwary individuals have switched the source and destination files and overwritten important things.

The only reason I can think to have a folder duplicated as you describe is an incremental back up. If THAT is what you're after then there are ways to do that... Depending on how specific and what kinds of files. System imaging being the easiest.

Every time I read up on Android I see these words so they must he important : always take a backup so you can restore if/when something goes wrong

Thanks for trying to help. I understand you are not familiar with the term 'synchronize'.
I will now go into detail of what it means and why it is important.

This has nothing to do with imaging or even copy/pasting.


Let's say your task is to work with a 10GB Folder which contains a large number of folders and files.
The total number of files in all the subfolders is fifty thousand. [This is NOTHING unusual, properties of MANY folders have tens of thousands of files, go around and look at properties of root folders..]
The total number of sub folders is four thousand [This is NOTHING unusual.]

This folder is identical on another device.


Here are some real world examples so you don't think this is strange.
• I have more than 500 music CDs, all which I transferred to my PC. My CDs folder consequently has about 10,000 files (songs) inside more than 500 sub folders (CDs).
• I have about 9 thousand pictures which were taken over the last twenty + years. My Photos folders consequently has 9,000 files inside hundreds of subfolders.
• I have a personal 10 GB folder with fifty thousand files inside four thousand folders. This is nothing unusual.

So if you delete one photograph out of the 9,000 you have...
Or if you if you add one song to the 10,000 you have...
If you make changes to fifty files out of the ten thousand your personal folder has....

What is the word you use to make sure those changes are replicated on another computer device which is storing replicas of all your music/pictures/files?

That word is synchronize. You synchronize Folder B to be the same as Folder A.


There are many, many programs for a PC that do this. Let's take a look at one of them.

Here we have folder A and Folder B:


With a single press of a button, the right folder will be **synchronized** with the left folder.


You are not alone. I am not sure why so many people do not know what synchronizing means and why it is important.


PLEASE understand that the CLOUD is *not* an effective solution. The process to synchronize fifty thousand files would take forever over the internet.
NOT EVEN Wi-fi is effective when you are dealing with multiple folders containing tens of thousands of files.

ONLY direct access to two folders is effective. No Cloud. No WiFi.

The only Android programs I found that can do this cannot sync sub folders, only single folder contents.

Well now I'm even more confused... But it's not your fault

I can see what you mean by sync but I'm confused as to how you are looking at it. What I mean is, do you want to maintain these folders on your pc (folder a) and have a sync folder (folder b) that replicated additions and deletions? I'm sorry but I can think of no way for that to happen with out the cloud. And I certainly can't think of how you would make a connection between pc and Android without a cable /WiFi etc.

If instead you would like two folder sync inside android then the guys on the Linux forum may be of some help. It would seem to me that creative work with file mounting would be a work around perhaps. A new fstab file could mount one folder in multiple locations making folder A and folder B actually the same folder accessible from both places , but I'm reaching to the end of my knowledge with these suggestions already and won't send you down that road without better knowledge. I really do think the Linux folk might have the answer.

knoober, to sync an SD card folder with a folder on the phone/tablet, would you please post why would I need the cloud or a PC for that?

c627627 said:

knoober, to sync an SD card folder with a folder on the phone/tablet, would you please post why would I need the cloud or a PC for that?

Click to expand...

You don't I misread and though you might mean sync with a folder A existing on a pc and folder B on your Android.


Now please do forgive me if the answer is obvious, but I cannot see a reason to have duplicate files on the same device (ie folder A on internal storage and folder B on removable SD card) as your phone /tablet can easily access and manipulate a directory from either location without the need for a second identical location.
However I know my lack of understanding does not solve your problem so I'll take a stab (it's a pun just go with it) at trying to explain how the fstab might be of help. Fstab (file system table) determines the mounting of different partitions and storage devices within your Android device (depends on your version exactly where it is and how many of them there are) but my theory is that you could create a folder A where you would like it to be (internal storage) and a folder b - also where you would like it to be (SD card storage) and use the fstab to mount folder C (your folder with all your files) into each location. Then whenever you access folder A or B to make changes folder C is where you will be working regardless. I'm sorry for the confusion earlier about the cloud, you don't need it

Here is some quick info on the fstab: https://en.wikipedia.org/wiki/Fstab

No need to apologize, your answers are very typical of my past experiences, so talking to you would help me reword my questions.

If you had a 10GB folder on an SD Card, how would you sync it with 3 devices, if the folder has thousands of subfolders and files? You would place the SD card inside each device and you would sync them directly. Any other method would take more time, where the word 'more' means thousands (and thousands) percent of time more when you use a stop watch to measure how quickly syncing can be done directly vs. using any wireless method.


So as you can see the SD card folder IS NOT permanently on the device, it's on a removable SD card, inserted for the sole purpose of making the sync process be quicker... A LOT quicker then if cloud syncing were used.

After the SD card is removed, I need to have a synced folder remain that is still on the device.

I know that http://www.xda-developers.com/ will probably be an excellent resource if you haven't been there already. I believe they have a section for app requests. I would simply tell them what app wasn't good enough and why. Or point them at this thread to read and then you won't need to explain yourself again. Best I got Google on Garth!

I've posted a thread there about this before.
I've been trying to do this for years, knoober. I've spent years looking at apps on Google Play and forums like xda.

I know how to install custom operating systems, root devices, I'd say my knowledge is above average.

DIRECT syncing two folders should not be a big deal and it isn't on PCs, but it is on Android.

c627627 said:

Syncing two folders should not be a big deal and it isn't on PCs, but it is on Android.

Click to expand...

Have you tried SpiderOak?
EDIT: Never mind, looks like their Android app is read-only to your synced stuff.

Tresorit says they support editing files on Android. I don't see any UI screenshots, so no idea how easy it is to sync arbitrary folders.

It says this is a "cloud technologies company". It wants me to create an account before using this app.

Why is the cloud necessary to sync two local folders!?!
Every-single-app I tried is a cloud sync app. It would take forever to cloud sync a folder. Forever when compared to mere SECONDS it would take if the cloud were NOT used.

The entire purpose of this thread's question is to find an app which DOES NOT use the cloud to sync.
I need a direct sync app. 'No INTERNET necessary sync' app. 'No connection of any kind necessary' app.

c627627 said:

It says this is a "cloud technologies company". It wants me to create an account before using this app.

Why is the cloud necessary to sync two local folders!?!
Every-single-app I tried is a cloud sync app. It would take forever to cloud sync a folder. Forever when compared to mere SECONDS it would take if the cloud were NOT used.

The entire purpose of this thread's question is to find an app which DOES NOT use the cloud to sync.
I need a direct sync app. 'No INTERNET necessary sync' app. 'No connection of any kind necessary' app.

Click to expand...

Then you're not looking for a sync app. You're looking for an Android-compiled rsync binary (and maybe a shell app to execute bash scripts).

petteyg359 said:

Then you're not looking for a sync app. You're looking for an Android-compiled rsync binary (and maybe a shell app to execute bash scripts).

Click to expand...

Maybe I am losing my mind.
I went to the official web site of the PC program I use just to see if synchronizing no longer means what it used to mean, and here's what I found in the screenshot below.


What is it that we used to do to folders before there was even such a thing as a smart phone, if not syncing?
Binary and scripts!? Not programs that simply sync two folders?

Am I the only one that has a need to sync a removable folder that can be carried with you on a microSD card anywhere and inserted into any device that takes microSD cards?

Direct syncing a sizeable folder is thousands of times (literally thousands of times) faster than cloud syncing.
Use a stop watch and you will see!

Pettyg isn't wrong, you basically want a compiled android version of rsync. Being able to merge two directories making changes on either side if they are made?

Similar to what microsoft has with the SyncTools powertoy application for Windows?

Just an FYI, you may have some problems synchronizing with newer version of android:
http://www.mediamonkey.com/support/...d-card-content-cant-be-synced-toediteddeleted

If you have your music folder and your pictures folder, and most importantly your 10GB files folder on an SD card, and you've made a single change in each of those three folders.

How would you quickly sync those three microSD card folders with three phones/tablets?


Cloud syncing tens of GB just to make changes to three relatively small files on a tablet/phone would be an exercise in insanity, would it not? Do you have any idea how long that would take?
But it would take a minute if synced directly from the SD card. Whereas it would take f-o-r-e-v-e-r to cloud sync the same task. And no one has a need to direct folder sync in the world of Android? Millions of people do this on a PC every day, and no one has any need to do this on a Tablet? Or a modern phone? I can't wrap my head around that at all.

I never said you needed to use cloud to do it...

Ideally the software (such as what was offered with rsync or with synctoy in windows) checks for differences in the folders (timestamps, new files, etc) and then merges/makes the changes across the folders.

To be fair, if you did it with cloud, would it not just take a while the first time then incrementals would be relatively quick?

Going back to the topic, what word, other than 'synchronize' would you use for what you just described?

Since no one here has ever heard of direct syncing on Android and since millions of people do this on a PC, given that Tablets/Phones are now PC replacements... how do you not find this to be beyond strange? Yes it would take unacceptably longer to cloud sync large folders.

Syncing the folders is the phrase I would use.

I guess an important question is: how much is the data changing regularly? If it is only adding a file here or there then the overall sync time between any devices would be very quick (as it would only pick up differences, not try to re-sync all 10GB every single time). Yes, the first time would suck having it wait, but after that it would be quick. If you are putting on 10GB of new data every time you use it, then obviously cloud syncing would not work for this purpose. I don't find this 'beyond strange' as I don't know anyone that keeps a significant amount of data on their phone/tablet that isn't being backed up to another location (networked) automatically, I don't know anyone that keeps duplicate copies of files on both their internal SD card and external SD card on purpose.