Appendix Troubleshooting


The following two general issues can result in failed synchronization:

  • The server setup is incorrect.

  • The client contains a bug.

When reporting bugs, it is helpful if you first determine what part of the system is causing the issue.

Identifying Basic Functionality Problems

Performing a general ownCloud Server test

The first step in troubleshooting synchronization issues is to verify that you can log on to the ownCloud web application. To verify connectivity to the ownCloud server try logging in via your Web browser. If you are not prompted for your username and password, or if a red warning box appears on the page, your server setup requires modification. Please verify that your server installation is working correctly.

Ensure the WebDAV API is working

If all desktop clients fail to connect to the ownCloud Server, but access using the Web interface functions properly, the problem is often a misconfiguration of the WebDAV API. The ownCloud Client uses the built-in WebDAV access of the server content. Verify that you can log on to ownCloud’s WebDAV server. To verify connectivity with the ownCloud WebDAV server, open a browser window and enter the address to the ownCloud WebDAV server. For example, if your ownCloud instance is installed at, your WebDAV server address is If you are prompted for your username and password but, after providing the correct credentials, authentication fails, please ensure that your authentication backend is configured properly.

Use a WebDAV command line tool to test

A more sophisticated test method for troubleshooting synchronization issues is to use a WebDAV command line client and log into the ownCloud WebDAV server. One such command line client — called cadaver — is available for Linux distributions. You can use this application to further verify that the WebDAV server is running properly using PROPFIND calls. As an example, after installing the cadaver app, you can issue the propget command to obtain various properties pertaining to the current directory and also verify WebDAV server connection.

CSync Unknown Error

If you see this error message stop your client, delete the ._sync_xxxxxxx.db file, and then restart your client. There is a hidden ._sync_xxxxxxx.db file inside the folder of every account configured on your client.

Please note that this will also erase some of your settings about which files to download.

See for more discussion of this issue.

Isolating Other Issues

Other issues can affect synchronization of your ownCloud files:

  • If you find that the results of the synchronizations are unreliable, please ensure that the folder to which you are synchronizing is not shared with other synchronization applications.

  • Synchronizing the same directory with ownCloud and other synchronization software such as Unison, rsync, Microsoft Windows Offline Folders, or other cloud services such as Dropbox or Microsoft SkyDrive is not supported and should not be attempted. In the worst case, it is possible that synchronizing folders or files using ownCloud and other synchronization software or services can result in data loss.

  • If you find that only specific files are not synchronized, the synchronization protocol might be having an effect. Some files are automatically ignored because they are system files, other files might be ignored because their filename contains characters that are not supported on certain file systems. For more detailed information see the Ignored Files section.

  • If you are operating your own server, and use the local storage backend (the default), make sure that ownCloud has exclusive access to the directory.

The data directory on the server is exclusive to ownCloud and must not be modified manually.

  • If you are using a different file backend on the server, you can try to exclude a bug in the backend by reverting to the built-in backend.

  • If you are experiencing slow upload/download speed or similar performance issues be aware that those could be caused by on-access virus scanning solutions, either on the server (like the files_antivirus app) or the client.

Log Files

Effectively debugging software requires as much relevant information as can be obtained. To assist the ownCloud support personnel, please try to provide as many relevant logs as possible. Log output can help with tracking down problems and, if you report a bug, log output can help to resolve an issue more quickly.

The client log file is often the most helpful log to provide.

Obtaining the Client Log File

There are several ways to produce log files. The most commonly useful is enabling logging to a temporary directory, described first.

Client log files contain file and folder names, metadata, server URLs and other private information. Only upload them if you are comfortable sharing the information. Logs are often essential for tracking down a problem though, so please consider providing them to developers privately.

Logging to a Temporary Directory

  1. Open the ownCloud Desktop Client.

  2. Press F12 or Ctrl-L or Cmd+L on your keyboard.

    The Log Output window opens.


  3. Enable the Enable logging to temporary folder checkbox.

  4. Later, to find the log files, click the Open folder button.

  5. Select the logs for the time frame in which the issue occurred.

That the choice to enable logging will be persist across client restarts.

Saving Files Directly

The ownCloud client allows you to save log files directly to a custom file or directory. This is a useful option for easily reproducible problems, as well as for cases where you want logs to be saved to a different location.

To save log files to a file or a directory:

  1. To save to a file, start the client using the --logfile <file> command, where <file> is the filename to which you want to save the file.

  2. To save to a directory, start the client using the --logdir <dir> command, where <dir> is an existing directory.

When using the --logdir command, each sync run creates a new file. To limit the amount of data that accumulates over time, you can specify the --logexpire <hours> command. When combined with the --logdir command, the client automatically erases saved log data in the directory that is older than the specified number of hours.

Adding the --logdebug flag increases the verbosity of the generated log files.

As an example, to define a test where you keep log data for two days, you can issue the following command:

owncloud --logdir /tmp/owncloud_logs --logexpire 48

Logging in the Console

If the ownCloud client isn’t able to start and immediately crashes the first two options are not available. Therefore it might need to be necessary to start the ownCloud client using the command line in order to be see the error message

On Linux and Mac simply open the terminal and run:

owncloud --logfile - --logflush

On Windows open a PowerShell and run the following command:

& 'C:\Program Files\ownCloud\owncloud.exe' --logfile - --logflush | Write-Host

Make sure to copy the whole command and adjust the path to your owncloud.exe, if you have chosen to install the client in a different path.

To further increase the verbosity of the output you can also combine these commands with the --logdebug argument.

Control Log Content

Thanks to the Qt framework, logging can be controlled at run-time through the QT_LOGGING_RULES environment variable.

Exclude log item categories

QT_LOGGING_RULES='gui.socketapi=false;sync.database*=false' \
  --logdebug --logfile <file>

Add HTTP logging entries

QT_LOGGING_RULES='sync.httplogger=true' \
  --logdebug --logfile <file>

Only show specific log item categories

QT_LOGGING_RULES='*=false;sync.httplogger=true' \
  --logdebug --logfile <file>

ownCloud server Log File

The ownCloud server also maintains an ownCloud specific log file. This log file must be enabled through the ownCloud Administration page. On that page, you can adjust the log level. We recommend that when setting the log file level that you set it to a verbose level like Debug or Info.

You can view the server log file using the web interface or you can open it directly from the file system in the ownCloud server data directory.

Need more information on this. How is the log file accessed? Need to explore procedural steps in access and in saving this file, similar to how the log file is managed for the client. Perhaps it is detailed in the Admin Guide and a link should be provided from here. I will look into that when I begin heavily editing the Admin Guide.

Webserver Log Files

It can be helpful to view your webserver’s error log file to isolate any ownCloud-related problems. For Apache on Linux, the error logs are typically located in the /var/log/apache2 directory. Some helpful files include the following:

  • error_log — Maintains errors associated with PHP code.

  • access_log — Typically records all requests handled by the server; very useful as a debugging tool because the log line contains information specific to each request and its result.

You can find more information about Apache logging at

Core Dumps

On macOS X and Linux systems, and in the unlikely event the client software crashes, the client is able to write a core dump file. Obtaining a core dump file can assist ownCloud Customer Support tremendously in the debugging process.

To enable the writing of core dump files, you must define the OWNCLOUD_CORE_DUMP environment variable on the system.

For example:


This command starts the client with core dumping enabled and saves the files in the current working directory.

Core dump files can be fairly large. Before enabling core dumps on your system, ensure that you have enough disk space to accommodate these files. Also, due to their size, we strongly recommend that you properly compress any core dump files prior to sending them to ownCloud Customer Support.