Usage Overview: PC-Phone USB Sync

This page is a copy of the overview in the app's Help tab, styled for better reading in this web page. If you've already read the overview in Help, you may want to skip ahead to the GUI Guide for finer-grained usage details. If you're looking for app start-up info, try App Packages. For general coverage of this app's essentials, read on here.

Introducing the App

Welcome to PC-Phone USB Sync — portable and private backup and sync.

This app makes content folders the same on your PCs, phones, and USB drives, much quicker than full copies can. It's available for Android in full and trial versions at the Play store, and as a free download for Windows, macOS, and Linux PCs at quixotely.com.

This app brings powerful, PC-level tools to all your devices. The content it manages is not just contacts and calendars. It's an entire folder of your choice, including its subfolders, and all the photos, documents, music, and other media that you value.

By using this app with a removable drive, you can both back up this content on your phone or PC to save it, and sync it between your devices to make it match: from PC to phone, from phone to PC, and any other way you find useful. Among its roles, this lets you:

Perhaps best of all, this app uses removable drives and USB ports for its backups and syncs, to avoid both slow networks and the privacy perils of clouds. With this app, your stuff remains your stuff, not someone else's point of control.

This page's sections present the bare-minimum info needed to use this app. They explore:

After reading the overviews here, you may wish to move on to the GUI Guide page for more in-depth coverage of all the GUI's options. First, this page presents enough usage fundamentals to help you start syncing well.

Usage Basics

This section provides a quick review of this app's usage model. Later sections go into more detail on specific usage modes, but the basics introduced here are straightforward.


Before we jump into syncs, let's cover a few preliminaries.

First off is terminology: in this app, content is an entire folder (a.k.a. directory) containing arbitrary files, including all its subfolders of any depth; syncs propagate changes from one content folder to another, on request; USB often implies any removable drive; PC means any Windows, macOS, or Linux computer; and phone refers to any device running Android 8 or later, including tablets.


Next up, to use this app, you'll need to set up a drive and one or more versions of the app itself. Specifically, this app's usage requirements vary per your goals:

For example, to sync your PC to or from a phone, get the Android app, the free version of this app for your PC, and a USB drive. To back up content only, get the app for your device plus a USB drive. There's more info about PC apps ahead.

For best results, removable drives used with this app should be formatted with the portable exFAT filesystem. All PCs and most phones support exFAT today, and most USB drives come preformatted with it. FAT32 works, but its timestamp limitations can trigger spurious syncs when your devices' time changes (more info), and other formats are not as portable. See the web for formatting tips.

Naturally, all the devices you'll be syncing to—USB drives, phones, and PCs—must have enough free storage space to hold a copy of your content folder (or folders, if you'll sync more than one). Most phones come with space to spare today, but bigger is better for content storage.

How to Use

With those preliminaries in hand, we're ready to sync some content. Let's start with the general model first; it's simpler than the full details may suggest.

When using this app, you'll first collect your content files in a folder (or folders) using your local file explorer or other tool, and copy it to your devices using this app. Use subfolders to organize your content as desired; everything in your folder will be synced in full.

After the initial copy, you'll make changes on one device at a time, and push them to other devices with this app whenever you wish. These change propagations (a.k.a. syncs) use your USB ports and removable drive, and vary by usage mode:

In both modes, this app supports automatic rollbacks (i.e., undos) for all the changes its syncs make on each device. This helps ensure the safety of your content. You can even undo multiple syncs to reset your content to a prior state in the past.

Beyond copies and syncs, this app also has tools for verifying the content copies you'll create, along with portability utilities, configuration options, and help resources. We'll explore these later.

How to Run

Finally, you'll implement the preceding section's model by running actions in the app, but this is similarly simple. All of the app's primary actions live on its Main tab; to run any one of them:

  1. Tap the blue FROM and TO button in the Main tab to select content folders
  2. Tap the red buttons in the resulting popups to pick storage types and folders
  3. Tap the green action button in the Main tab to process your choices

You can usually skip right to step 3, because the app remembers your prior choices. Each action opens a popup to explain what it will do, remind you of your folder picks, and confirm its run. Main-tab actions all launch operations in the open-source Mergeall system, which is included with the app, and can be explored here and here.

To monitor an action's progress and results, inspect its logfile in the Logs tab: pick a file there, and click a green action button to view. TAIL shows the file's end, WATCH updates its tail view every second, and OPEN and EXPLORE open logfiles in full.

For ease, Logs automatically selects and scrolls to the most-recent logfile at the top of its date-sorted list for fast access. As of 1.1.0, you can also use double and triple taps on logfile names in the Logs tab to quickly run TAIL and TAIL+OPEN, respectively, and the popup shown on action exit includes brief logfile summary information.

Logfile reports are straightforward, and include indicator lines at the end if there are any messages that warrant investigation (these appear in exit summaries too). If you see an indicator line, search logfiles for "*" to locate errors and notes, and see Tech Notes in this app's User Guide for more about logfiles in general.

Although it supports a variety of actions, this app's main tool is the SYNC button on its Main tab. This makes a TO folder the same as a FROM folder quickly, by updating TO only for changes made in FROM. SYNCs detect changes by checking timestamps, sizes, and structure, to avoid slower full copies. They can also be rolled back with UNDO if needed.

The way you'll use SYNC depends on whether you want to back up your content, sync it between PCs and phones, or both. The next two sections provide step-by-step coverage of both usage modes.

Content Backups

To use this app to back up content folders on your PC or phone, you'll need a removable USB drive to host the backup copy, and versions of this app for each device you'll be backing up. Get the Android version for your phones, and one of the free versions of this app for your Windows, macOS, or Linux PCs.

See the tips above for more on the USB drive, and open this site's App Packages guide to fetch both Android and PC versions of this app. For backups, you'll copy content first, sync it later after changes, and verify it as desired, as the next sections explain.

Initial Copy

To get started, run an initial content-folder copy from your PC or phone to your USB drive, by selecting folders and using the app's COPY button once:

  1. Attach your USB drive to your PC or phone
  2. Select your PC or phone folder as FROM, and a USB-drive folder as TO
  3. Run the app's COPY

In step 2, you're choosing a folder on your USB drive to host the content copy: FROM's content folder is added to TO as a new subfolder. This first copy may be slow because it must copy your content in full, but later backups will be fast.

Later Backups

Thereafter, whenever you want to update your backup copy, run SYNC just once, with the PC's or phone's content copy as FROM, and the USB drive's copy as TO:

  1. Attach your USB drive to your PC or phone
  2. Select your PC or phone folder as FROM, and your USB-drive folder as TO
  3. Run the app's SYNC

In step 2, you're choosing existing content-copy folders. Every time you run all three steps, your backup drive's content copy will be made the same as your device's copy.

These updates will be fast, because they change your USB drive's copy only for changes you've made on your PC or phone. Moreover, because the app remembers your FROM and TO settings between runs, you'll normally need to just attach your drive and press SYNC.

Keep in mind that the app's SYNC button is used for both content backups and device syncs. Here, it makes a backup copy the same as a live copy quickly, and works as an incremental backup tool. Device syncs ahead will use it as a more general change-propagation tool.

Verify and Restore

To verify that your backup copy matches your device, attach your USB drive to your device and select as above, then run either SHOW or DIFF in the app. SHOW runs a fast timestamp-based comparison of FROM and TO; DIFF runs a complete byte-for-byte comparison, but is much slower because of this, and should be used only occasionally.

To restore your content from a backup, simply select the USB drive's content copy as FROM and your device as TO, and either SYNC to an existing copy, or COPY the USB drive's copy in full. Once restored, you can SYNC to your USB drive again to back up when desired.

Note that the UNDO button can roll back changes made to your USB drive's copy by a SYNC, but is rarely useful in backups mode. Also note that if you opt to sync PC and phone devices, your USB drive will automatically serve as a backup copy of your content, and no extra backup steps are required. To see how, we have to move on to the next section.

Device Syncs

To use this app to sync content folders between PCs and phones, you'll need a removable USB drive to serve as a go-between for syncs, and versions of this app for each device you'll be syncing. Get the Android version for your phones, and one of the free versions of this app for your Windows, macOS, or Linux PCs. See the USB drive tips above, and open this site's App Packages guide to fetch Android and PC versions of this app.

Device syncs always update a destination device to match a source device, but can run in any direction. For instance, they can be run from PC to phone, from phone to PC, or between any combination of PCs and phones, and you need PC versions of this app only if there are PCs in the mix. Here, we'll focus on typical PC/phone syncs.

Device syncs also use an intermediate USB drive to propagate content and changes between your devices. This just means you'll run the app twice: once on the source to push to the USB drive, and then again on the destination to pull from the USB drive.

By syncing to and from a go-between USB drive this way, your content copies on your PC and phone are made the same without being directly connected, and without compromising privacy. As a bonus, your USB drive becomes an extra backup copy of your content.

The following sections detail the steps you'll run to copy your content initially, sync it for changes later, and verify your content copies as desired.

Initial Copy

To get started, run an initial content-folder copy from your PC to your phone, using your USB drive as a go-between, and running the Main tab's COPY on each device:

  1. On your PC:
    1. Attach your USB drive
    2. Select your PC's folder as FROM, and a USB drive folder as TO
    3. Run the app's COPY
  2. On your phone:
    1. Attach your USB drive
    2. Select your USB drive's folder as FROM, and a phone folder as TO
    3. Run the app's COPY

In both selection steps, you're choosing a folder on the destination to host the content copy: FROM's content folder is added to TO as a new subfolder. If your content lives on your phone initially, do the same as above, but swap PC and phone roles: copy phone to USB, then USB to PC.

Either way, the net result makes your content folder the same on your PC, phone, and USB drive. This first copy may be slow because it has to perform a full byte-for-byte copy, but later syncs will be much faster because they'll update TO only for changes in FROM.

PC-to-Phone Syncs

After the initial copy, whenever you want to update your devices' content copies to be the same, simply run SYNC twice: once on the source device to sync to the USB drive, and then again on the destination device to sync from the USB drive.

For example, to sync your phone's content copy to reflect changes made in your PC's content copy, simply run SYNC on each device with the USB drive in between:

  1. On your PC:
    1. Attach your USB drive
    2. Select your PC's folder as FROM, and your USB drive's folder as TO
    3. Run the app's SYNC
  2. On your phone:
    1. Attach your USB drive
    2. Select your USB drive's folder as FROM, and your phone's folder as TO
    3. Run the app's SYNC

In both selection steps, you're choosing existing content-copy folders. Every time you run this procedure, it updates your phone for changes made on your PC, and makes your content copies the same again on your PC, USB drive, and phone.

Just as in backups, because this app automatically remembers the FROM and TO paths you used for prior runs on each device, the selection steps above aren't required for later runs if you sync the same way each time: simply attach your USB drive and press SYNC on both PC and phone.

Phone-to-PC Syncs

Likewise, to sync your PC's content copy to reflect changes made in your phone's content copy, simply run SYNC on each device with the USB drive in the middle:

  1. On your phone:
    1. Attach your USB drive
    2. Select your phone's folder as FROM, and your USB drive's folder as TO
    3. Run the app's SYNC
  2. On your PC:
    1. Attach your USB drive
    2. Select your USB drive's folder as FROM, and your PC's folder as TO
    3. Run the app's SYNC

Just like PC-to-phone syncs, you're choosing existing content-copy folders in both selection steps, and your content copies on your phone, USB drive, and PC are made the same again every time you run this. And here too, the selection steps above can often be skipped, because FROM and TO paths are saved on both your phone and your PC: just attach and SYNC.

Verify, Restore, and Undo

To verify that your device copies are the same, first verify your USB drive's copy to one device, then verify it to the other. If the USB drive's copy matches both devices, then the device copies are the same too (abstractly speaking: if A = B and B = C then A = C).

More concretely, to verify that your content copies match, attach your USB drive to your device, select one copy as FROM and the other as TO (the direction doesn't matter here), and run either SHOW or DIFF in the app. SHOW runs a fast timestamp-based comparison of FROM and TO; DIFF runs a complete byte-for-byte comparison, but is much slower because of it, and should be used only occasionally.

Also note that because your USB drive will always store an extra backup copy of your content, you can use it at any time to restore your PC, phone, or both: just run the app with your USB drive as FROM and your device as TO, and either SYNC (if the device's copy is usable) or COPY (to copy the content folder to the device in full and anew).

Finally, the app's UNDO button allows you to roll back all the changes made to TO by the most recent SYNC run against it. This is a last-resort safety mechanism which you can use when syncs go awry, and fully restores TO to its pre-SYNC state. Though more rarely needed, you can also undo multiple SYNCs one at a time with multiple UNDOs: each one resets the TO folder to its state further in the past.

Important: UNDO works only if backups are enabled in the Config tab, which makes SYNC save changed items in TO's __bkp__ folder. This is enabled by default, and should generally be left this way; disabling SYNC backups can save some space and runtime, but means that SYNC changes are permanent. Mod with care.

More Essentials

This last section dives deeper into additional topics that you'll find important as you start using this app. Some of the topics here are covered further in other parts of this app's docs, as noted along the way. In this section:


Because syncs run in just one direction, you'll want to make changes on only one device at a time. Designate one device as changeable, and sync its content copy to other devices before making changes on them. The advantage of this policy is that you can't accidentally lose changes if the same item is changed differently on two devices in between syncs. If you inadvertently change content this way, you'll need to resolve the differences manually before resuming syncs with this app. Inspect differences with the app's SHOW to find any offenders before SYNC.


You can mod both the appearance and behavior of this app in a variety of ways, in its Config tab. This tab describes available settings, which are saved between app runs if you tap the tab's "Save Changes" button. As noted earlier, the app also saves Main-tab FROM and TO paths automatically after an action run, so you don't need to reselect. For finer-grained Config details, please see the GUI Guide.


To use this app, organize the content files you wish to back up or sync into folders as noted earlier. You can create and sync multiple content folders, but it's usually easier and quicker to use just one for all your content, or at least one for content that's prone to change. Use subfolders in your main folder to organize content by types, and sync either the main folder or individual subfolders.

You'll also need to choose a location to host your content folder on each device. The Main tab's folder choosers, opened by its blue buttons, allow you to pick folders in on-PC, on-phone, and USB-drive storage. Storage types are called out by name in the red radio buttons at the top of the chooser popup: scroll to see all of your storage types, and tap to go to a type's root folder at any time.

You can store your content anywhere in any storage type, but it must be accessible to this app, as well as file explorers and programs you'll use for content views and changes. Here are some tips on storage options per device type.

On PCs
You'll normally create a content folder in your on-PC home (a.k.a. account) folder, which choosers label as PC because it's the recommended location. Choosers also display a ROOT folder on PCs which gives access to your entire system drive (disable in the Config tab if unused), and Linux shows an OS for the Windows drive on dual-boot setups.
On Android
Internal on-phone storage comes in multiple flavors, with differing access rules and longevity. The most useful of these are made available as PHONE and APP in the Main tab's choosers:

Android can optionally also display root folders as ROOT, but this requires a rooted phone to be useful, and is presently experimental. Enable it in the Config tab.

On USB drives
This category includes both SSDs and flash drives attached by USB port. Your drive's name shows up in the app's folder choosers (e.g., MYSSD) on all platforms. If you attach more than one drive, each drive's name appears, and USB hubs work in this app on both PCs and Android. Almost anywhere goes for content folders on such drives, though the drive's top level makes selection easier. Note: if you're using Android 10 or earlier, your options in this category are constrained; see the special case below.
On other media
In addition to PC, phone, and USB-drive storage, you can also select and use microSD cards, optical disks, and network drives as FROM or TO in this app, if the host device makes them accessible to this app. Generally, Android phones support microSD cards, and PCs support all three media types. Here's a brief rundown on each.

If present, the names of microSD cards will appear alongside other storages in folder choosers. On Android devices, such cards may be either embedded or attached, but embedded mode is increasingly rare and can't match USB's convenience, and microSD in either mode is likely slower than other USB drives.

Optical storages, including attached BDR and CD-ROM disks, also show up in the app's folder choosers and are fully supported as content sources where available. These storages are generally usable on all PCs, and may be useful for accessing content copies burned to disks for comparisons or restores.

Remote storages, including network shares and virtual-machine access points, are also listed in choosers and supported in full if present. These storages work on PCs if mounted to a standard folder on Unix or mapped to a drive letter on Windows, though USB drives are generally recommended over networks for portability, speed, and privacy. There's more on network drives here.

Special case for removables on Android <= 10
In this app, you can read and update any location on removable (e.g., USB and microSD) drives in Android 11 and later. On Android 10 and earlier you can read from anywhere on removables too, but you can update such drives only in a folder specific to this app: com.quixotely.usbsync in the drive's Android/data (the app-folder name ends in .usbsynctrial for the trial version).

This means that on older Androids you should host content in this specific folder on removable drives if it will be either backed up from your phone or synced from your phone to your PC. Content used only in PC-to-phone syncs, or on newer Androids in general, need not follow this rule. Either way, this app will always warn you if you select an invalid removable folder for Main-tab actions that may modify it on older Androids.

For more background on storage types, please see the GUI Guide's coverage of the folder chooser.


Although this app runs on both PCs and Android, some exotic content items may not be fully portable due to interoperability constraints on some devices. The good news is that nearly all content consists of normal files and folders, which can always be processed by this app on all devices without loss or error. If your content follows this norm, you can safely ignore most portability concerns.

Rarer items such as symlinks and Unix permissions, however, may not survive journeys through devices which cannot store them. In this app, Unix permissions are copied to the extent allowed by the destination, and symlinks are skipped with logfile error messages when copied to devices that don't support them. This rule applies to both the SYNC and COPY actions in the app.

While some platforms (e.g., macOS) silently forge symlinks with simple files, this hack can fail in some later usage contexts, and would yield perpetual file-type differences if used by this app. Your best option is to omit symlinks in content folders which may be copied to less-supportive devices. For more info, see the Tech Note.

Some filenames created on Unix (and some Android storage types) can't be stored on all devices either, but these can be automatically adjusted to be portable with the Main tab's NAME action. For more details, please see the full User Guide's coverage of the NAME action here; use this action's report-only option to check before changing.

In addition, this app's Config tab includes an option, enabled by default, to skip platform-unique items that don't belong in cross-platform content; see the GUI guide's Config coverage for more info. Though rare and obscure, macOS's Unicode policies may also pose pitfalls for some filenames; see the Tech Note for coverage and fixes.


Main-tab actions are run one at a time; you can't start another until a running action finishes. Once started, they never block the app's GUI, and always continue running both if you navigate to another app, and if your screen blanks on Android due to timeout or power-button press. This means you can freely use other apps and turn off your screen without pausing a long-running action in progress.

On PCs, Main-tab actions run in parallel threads, which never pause if the GUI is minimized or loses focus, and stop only if you close the app itself (and confirm the close). On Android, actions by default run as foreground-service processes, but can optionally be run as threads. You can simply use the default and don't need to know about processes and threads to use this app, but it may help to know the basic differences.

Android foreground services post a notification while running, to let you know when an action finishes; please allow notifications when prompted on the first run. Threads do not post notifications, and are enabled by unchecking "Run Main actions..." in the Config tab; they are turned on in Android 8 for implementation reasons, but are otherwise not required. Actions run equally fast in both Android modes, and as quick as equivalent command lines in the Termux app.

Also on Android, the app doesn't allow itself to be closed with a Back button on the Main tab when an update action is running, because this could harm your content. Else a thread would be killed with the app, and a service would keep running but be impossible to detect reliably on app restarts. To unconditionally close the app and any running action, use a swipe on your phone's Recents (i.e., open apps) display instead.

Tips: on some Android devices, turning on the Logs tab's WATCH to monitor action output can make the action run significantly faster, due to Android's scheduling policies; this may yield a 10x speed increase on some phones, but has no impact on others. See also the About tab's Android note about battery optimizations; no issues are known and multi-hour runs for very large content work well, but you may need to change power settings on some phones if this app's actions are killed (see also memory, speed, and power notes in App Packages and the related Tech Note).


On Android, this app requires only general storage permission on Android 10 and earlier, and the All Files Access permission on Android 11 and later. These allow the app to access your content folders stored in both on-phone shared storage and your USB drive. Because these are crucial on Android, you'll be prompted to enable these permissions on the app's first run, as well as by folder choosers and Main-tab actions if not yet enabled. You'll also be prompted to restart the app once after granting these permissions, where needed.

On Windows and Linux PCs, this app requires no storage permissions; you can store your content folders in any PC or USB-drive location that you have permission to access. The same is generally true for macOS, but that platform has storage-access rules that are more convoluted and prone to change.

Specifically, macOS will ask you to enable removable drives and certain folders when they are first accessed, and the app's first-run dialogs mention macOS's Full Disk Access permission as an option. Full Disk Access may help the app use items considered sensitive by macOS, but it is not required for typical content folders.

Regardless of permissions, this app never accesses any items on any platform unless you instruct it to do so. Moreover, this app holds no Internet permissions, and accesses it only when you ask it to open its own online resources with an app of your choosing.


Last but far from least, this app is private by design. It never does anything with your content, except to move it between your own devices, and only on your explicit requests. Your content is never silently changed, broadcast across the Internet, stored on remote cloud servers, or harvested in any way for information. In short, this app respects the fact that your digital content is your personal property — and encourages other software to do the same.

For More Info

And that brings us to the end of this usage overview. For this app's terms of use, tools used, and other logistics, see its About tab. For more detailed usage info, please move on to the GUI Guide.