-With Azure Active Directory authentication context, you can enforce more stringent access conditions when users access SharePoint sites that have a sensitivity label applied. Authentication contexts are used with sensitivity labels to connect Azure AD conditional access policies to labeled sites. For details, see [Manage site access based on sensitivity label](authentication-context-example.md).

-Microsoft PowerShell cmdlets that you use in SharePoint Server help you complete simple and complex administrative tasks. Command-line Help is available in the SharePoint Management Shell. For information about PowerShell in general, visit [SharePoint Powershell ](/powershell/sharepoint/index?view=sharepoint-ps&branch=master).

- Issues in your environment can affect the success of upgrade, and unnecessary or very large amounts of data can affect upgrade performance for both databases and site collections. If you don't need something in your environment, consider removing it before upgrade. If there are issues detected, try to resolve them before you start to upgrade. .

-[Overview of Design Manager in SharePoint 2013](/sharepoint/dev/general-development/overview-of-design-manager-in-sharepoint)

-| |Step|Notes|

-||||

-|[ ]|**Create an inventory of server-side customizations in the environment** <br/> Create an inventory of the server-side customizations in your environment (solutions, features, Web Parts, event handlers, master pages, page layouts, CSS files, and so on). Record all customizations needed for your environment in the upgrade worksheet. <br/> Detailed steps: [Identify and install customizations](use-a-trial-upgrade-to-sharepoint-2013-to-find-potential-issues.md#Customizations) in the "Use a trial upgrade to find potential issues" article.|Complete this step for the whole environment. Check each web server to make sure that you don't miss any customizations. Keep the inventory up to date as you prepare for the upgrade.|

-|[ ]|**Clean up your environment** <br/> Before you begin to upgrade, make sure that your environment is functioning in a healthy state and that you clean up any content that you do not have to upgrade. Clean up any orphaned sites or data, address any large lists and large ACLs, remove extraneous document versions, and remove any unused templates, features and Web Parts. <br/> Detailed steps: [Clean up an environment before an upgrade to SharePoint 2013](clean-up-an-environment-before-an-upgrade-to-sharepoint-2013.md).|Complete this step one time for the whole environment. <br/> This process might take days or weeks to finish.|

-|[ ]|**Test the upgrade process** <br/> Try out upgrade in a test environment to find any issues and determine how long your actual upgrade might take. <br/> Detailed steps: [Use a trial upgrade to SharePoint 2013 to find potential issues](use-a-trial-upgrade-to-sharepoint-2013-to-find-potential-issues.md)|Perform this step multiple times, until you are prepared to perform the actual upgrade.|

-|&nbsp;|Step|Notes|

-||||

-|[ ]|**Install and configure SharePoint 2013 and any language packs** <br/> Install the prerequisite software, and then install and configure SharePoint 2013.|Complete these steps on each server in your farm. <br/> This step might take one hour or more, depending on the number of servers are in your environment.|

-|[ ]|**Configure service applications** <br/> Enable and configure the services that you need in your new environment. <br/> Do not configure the following service applications - you will configure them while you upgrade their databases later in the process: <br/> Business Data Connectivity service <br/> Managed Metadata service <br/> PerformancePoint services <br/> Search <br/> Secure Store service <br/> User Profile service|Complete this step one time for the whole environment.|

-|[ ]|**Configure general farm settings** <br/> Reapply any general farm settings that you must have from your previous farm ΓÇö such as blocked file types, e-mail setting, and quota settings ΓÇö and add users or groups to the Farm Administrators group. Configure new settings such as usage and health data collection, diagnostic logging, and mobile accounts.|Complete this step one time for the whole environment.|

-|&nbsp;|Step|Notes|

-||||

-|[ ]|**Record the passphrase for the Secure Store service application** <br/> The Secure Store service application uses a passphrase to encrypt information. You must record this passphrase so that you can use it in the new environment.|Complete this step one time for each Secure Store service application in the environment.|

-|[ ]|**Set the previous version databases to be read-only** <br/> If you want your original environment to remain available to users in a read-only state, set the databases to read-only before you back them up.|Complete this step for each content database in your environment. <br/> Depending on your organization, you might need a database administrator to complete this step.|

-|[ ]|**Back up databases** <br/> Back up all the content databases and the following service application databases before you begin the database attach upgrade process: <br/> Business Data Connectivity <br/> Managed Metadata <br/> PerformancePoint <br/> Search Administration <br/> Secure Store <br/> User Profile: Profile, Social, and Sync databases|Complete this step for each content database and supported service application database in your environment. <br/> This step can take an hour, several hours, or longer, depending on your dataset and your environment. <br/> Depending on your organization, you might need a database administrator to complete this step.|

-|[ ]|**Export the encryption key for the User Profile service application** <br/> The User Profile Service service application requires an encryption key that is stored separately from the database and is needed if you want to upgrade the User Profile Sync database.|Complete this step one time for each User Profile service application in the environment.|

-|[ ]|**Restore a backup copy of the databases** <br/> Restore the databases from the backup.|Complete this step for each content database and supported service application database in your environment. <br/> This step can take an hour or longer, depending on your dataset and your environment. <br/> Depending on your organization, you might need a database administrator to complete this step.|

-|[ ]|**Set the restored databases to be read-write** <br/> Before you can attach and upgrade the databases that you copied to the new environment, you must set them to read-write.|Complete this step for each content database and supported service application database in your environment. <br/> Depending on your organization, you might need a database administrator to complete this step.

-|&nbsp;|Step|Notes|

-||||

-|[ ]|**Start the service application instances** <br/> Start the following service instances from Central Administration: <br/> Business Data Connectivity service <br/> Managed Metadata service <br/> PerformancePoint services <br/> Secure Store service <br/> User Profile service <br/> Start the instance of the Search service application by using PowerShell.|Complete this step one time for the whole environment.|

-|[ ]|**Upgrade the Secure Store service application** <br/> Use PowerShell to create the new service application and upgrade the database, create a proxy and add it to the default proxy group, and then restore the passphrase from the previous environment.|Complete this step one time for each Secure Store service application in the previous environment.|

-|[ ]|**Upgrade the Business Data Connectivity service application** <br/> Use PowerShell to create the new service application and upgrade the database. You do not have to create a proxy for the Business Data Connectivity service application. <br/> > [!NOTE]> The Business Data Connectivity service application is available in both SharePoint Foundation 2013 and SharePoint 2013.|Complete this step one time for each Business Data Connectivity service service application in the previous environment.|

-|[ ]|**Upgrade the Managed Metadata service application** <br/> Use PowerShell to create the new service application and upgrade the database, and then create a proxy and add it to the default proxy group. You must upgrade the Managed Metadata service application before you can upgrade the User Profile service application.|Complete this step one time for each Managed Metadata service application in the previous environment.|

-|[ ]|**Upgrade the User Profile service application** <br/> Use PowerShell to create the new service application and upgrade the database, and then create a proxy and add it to the default proxy group. After you have created the User Profile service application, you must import the Microsoft Identity Integration Server Key (MIIS) encryption key. Finally, you can start the User Profile Synchronization service.|Complete this step one time for each User Profile service application in the previous environment.|

-|[ ]|**Upgrade the PerformancePoint Services service application** <br/> Use PowerShell to create the new service application and upgrade the database, and then create a proxy and add it to the default proxy group.|Complete this step one time for each PerformancePoint Services service application in the previous environment.|

-|[ ]|**Upgrade the Search service application** <br/> Use PowerShell to create the new service application and upgrade the database, and then create a proxy and add it to the default proxy group. <br/> > [!NOTE]> This step applies to only SharePoint 2013. Although SharePoint Foundation 2013 includes search functionality, it is not the same Search service application that is in SharePoint 2013 and it cannot be upgraded.|Complete this step one time for each Search service application in the previous environment.|

-|[ ]|**Verify that all of the new proxies are in the default proxy group** <br/> Use the **Get-SPServiceApplicationProxyGroup** cmdlet to verify that all of the service application proxies are in the default proxy group.|Complete this step one time for the whole environment.|

-|&nbsp;|Step|Notes|

-||||

-|[ ]|**Create and configure web applications** <br/> Create a web application for each web application that existed in the old environment. If the desire is to use Windows Claims Authentication, create the new Web Applications in Windows Claims mode instead of Classic mode.<br/>|Complete this step one time for the whole environment.|

-|[ ]|**Reapply server-side customizations** <br/> Manually transfer all server-side customizations to your new farm. Refer to the inventory that you created in the upgrade worksheet to make sure that you install all components that your sites depend on to work correctly. When you install solutions, make sure that you add it to the appropriate path (/14 or /15). If you want a solution to be available to both paths, install it two times, and the second time use the **CompatibilityLevel** parameter when you install it, and it will be installed to the /15 path.|Make sure that you reapply customizations to all web servers in the farm.|

-|[ ]|**Verify custom components** <br/> Use the **Test-SPContentDatabase** Microsoft PowerShell cmdlet to verify that you have all the custom components that you need for that database.|Complete this step for each content database in your environment. <br/> Running the cmdlet takes only a few minutes, but addressing issues might take longer.|

-|&nbsp;|Step|Notes|

-||||

-|[ ]|**Attach a content database to a web application** <br/> Attach the content database that contains the root site collection first. For My Sites, attach the content database that contains the My Site host before attaching databases that contain the My Sites. <br/> You must perform this action from the command line. Use the **Mount-SPContentDatabase** Microsoft PowerShell cmdlet.|Complete this step for one content database in your environment. <br/> This step might take several minutes or several hours, depending on your dataset and hardware on the web servers, database servers, and storage subsystem.|

-|[ ]|**Verify upgrade for the first database** <br/> Verify that upgrade succeeded for the first database, and review the site to see whether there are any issues. <br/> Detailed steps: [Verify database upgrades in SharePoint 2013](verify-upgrade.md).|Complete this step for the content database that you just attached.|

-|[ ]|****Attach remaining databases**** <br/> Attach and upgrade the remaining content databases in your environment. You must complete this action from the command line.|Complete this step for each of the remaining content databases in your environment. <br/> This step might take several minutes or several hours, depending on your dataset, whether you are upgrading multiple databases in parallel, and the hardware on the web servers, database servers, and storage subsystem.|

-|[ ]|**Monitor upgrade progress** <br/> Use the Upgrade Status page in the SharePoint Central Administration website to monitor progress as your databases are upgraded. <br/> Detailed steps: [Verify database upgrades in SharePoint 2013](verify-upgrade.md).|Complete this step for each content database that you upgrade. <br/> This step might take several minutes, an hour, several hours, or days, depending on your content.|

-|[ ]|**Verify upgrade for the remaining database** <br/> Verify that upgrade succeeded for the remaining databases. <br/> Detailed steps: [Verify database upgrades in SharePoint 2013](verify-upgrade.md).|Complete this step for each of the remaining content databases in your environment. <br/> This step might take several minutes, an hour, several hours, or days, depending on your content.|

-|&nbsp;|Step|Notes|

-||||

-|[ ]|**Verify that site collections are working as expecting in 2010 mode** <br/> Review the site collections and make sure that they work in 2010 mode before you begin to upgrade any site collections. You can use a similar review list as the one provided for upgraded sites in [Review site collections upgraded to SharePoint 2013](review-site-collections-upgraded-to-sharepoint-2013.md) <br/> > [!NOTE]> If the SharePoint 2013 Web Application was created in Windows Claims mode, complete the next step prior to testing site collections.|Complete this step one time for your whole environment.|

-|[ ]|**Migrate user accounts to claims authentication, if it is necessary** <br/> By default, new web applications in SharePoint 2013 use claims authentication. If you were using classic authentication in the previous environment, you must migrate the users to claims authentication. For more information, see [Migrate from classic-mode to claims-based authentication in SharePoint 2013](migrate-from-classic-mode-to-claims-based-authentication-in-sharepoint-2013.md).|Complete this step one time for every web application that has changed authentication methods.<br/>|

-|[ ]|**Update links that are used in any upgraded InfoPath form templates** <br/> For a database-attach upgrade, you exported and imported all InfoPath form templates in your environment when you created the new environment. After upgrade, you can now update the links that are used in those upgraded form templates to point to the correct URLs by using a Microsoft PowerShell cmdlet. <br/> For more information, see [Configure InfoPath Forms Services (SharePoint Server 2010)](/previous-versions/office/sharepoint-server-2010/cc262263(v=office.14)).|Complete this step one time for your whole environment.|

-|[ ]|**Configure your Search topology** <br/> The architecture for the Search service has changed for SharePoint 2013. Plan and configure your Search topology to suit your environment and the new architecture. For more information, see [Scale search for Internet sites in SharePoint Server](../search/scale-search-for-internet-sites.md) and [Manage the search topology in SharePoint Server](../search/manage-the-search-topology.md).|Complete this step one time for your whole environment.|

-|[ ]|**Start a full crawl** <br/> After all content is upgraded and all settings are configured, you can start a full search crawl of your content. For more information, see [Start, pause, resume, or stop a crawl in SharePoint Server](../search/start-pause-resume-or-stop-a-crawl.md).|Complete this step one time for your whole environment. <br/> A full crawl can take several hours or days to complete, depending on how much content is in your environment.|

-|[ ]|**Back up your farm** <br/> Back up your farm so that you have a current backup of your upgraded environment before you start to upgrade site collections. For more information, see [Back up farms in SharePoint Server](../administration/back-up-a-farm.md).|Complete this step one time for your whole environment.|

-Before you start to upgrade from SharePoint 2010 Products to SharePoint 2013, you should make sure that your environment is functioning in a healthy state and that you clean up any content that you do not have to upgrade. You can also take the time to remove or rearrange content so that you will have the structure that you want after you perform the upgrade.

-You do not want to upgrade content that you do not have to keep. If it was unused for a long time and is not needed in the future, back it up, and then delete it to free storage and administrative resources, improve upgrade performance, and reduce upgrade risk. Be sure to communicate with site owners or organizational contacts regarding the site status ΓÇö you want to make sure that the site is not needed before you delete it (for example, you do not want to delete sites that are required for compliance, such as emergency procedures, even though they may not be frequently updated).

-By default, large list query throttling is turned on in SharePoint 2010 Products. This behavior has not changed in SharePoint 2013. If a list is very large, and users use a view or perform a query that exceeds the limit or throttling threshold, the view or query will not be permitted. If you are upgrading content from the server products in the Office 2007 release, check any large lists and have the site owner or list owner address the issue. For example, they can create indexed columns with filtered views, organize items into folders, set an item limit on the page for a large view, or use an external list. For more information about large list throttling and how to address issues with large lists, see [Manage lists and libraries with many items](https://go.microsoft.com/fwlink/p/?LinkId=251456).

-If you have 5,000 or more site collections in a database, consider breaking them out into multiple databases. In SharePoint 2010 Products, there was a default warning at 9,000 site collections and a hard limit at 15,000 site collections. In SharePoint 2013, these values change to 2,000 site collections for the warning and 5,000 site collections for the limit. To avoid errors during upgrade or broken sites after upgrade, we recommend that you move some site collections into separate databases. If you have multiple content databases, you can also speed up an upgrade process by upgrading multiple databases in parallel.

-Large numbers of document versions can slow down an upgrade significantly. If you do not have to keep multiple versions, you can have users delete them manually or use the object model to find and remove them. For more information about how to programmatically remove extraneous versions, see [Versions Web Service](/previous-versions/office/developer/sharepoint-services/ms772545(v=office.12)) on MSDN.

-First, verify that no sites are using the template, feature, or Web Part. You can use the **Stsadm -o EnumAllWebs** operation with the - **includefeatures** and - **includewebparts** parameters to identify these customizations in your environment. This operation identifies Web Parts, features, event handlers, and setup files that are being used in your environment. The **EnumAllWebs** command also specifies which files are used by which sites. Changes were made to the **EnumAllWebs** command in the February 2011 Cumulative update to make it return both site collection and web-level features. For more information, and to get the cumulative update, see [Description of the SharePoint Foundation 2010 cumulative update package (SharePoint Foundation server-package): March 3, 2011](https://go.microsoft.com/fwlink/p/?LinkId=254687).

-You can remove a feature during site collection upgrade. Simple features can also be removed by deprecating them in the template. You can use feature upgrade to remove more complex features. For more information, see [Upgrading Features](/previous-versions/office/developer/sharepoint-2010/aa544511(v=office.14)) and [Feature Upgrade Overview](/previous-versions/office/developer/sharepoint-2010/ee535723(v=office.14)) on MSDN.

-For more information about how to identify customizations in your environment, see [Use a trial upgrade to SharePoint 2013 to find potential issues](/previous-versions/office/sharepoint-server-2010/cc262155(v=office.14)). If customizations are not being used, delete them. For more information about how to manage these kinds of customizations, see [Features and Templates](/previous-versions/office/developer/sharepoint-services/ms439657(v=office.12)) and [Solutions and Web Part Packages](/previous-versions/office/developer/sharepoint-services/ms413687(v=office.12)) on MSDN.

-These sites and site templates are not available in SharePoint 2013 because the Office Online Server are now installed separately from the SharePoint 2013 environment. Sites based on these templates will not work in SharePoint 2013. Remove these types of sites before you upgrade.

-You cannot upgrade FAST Search Center sites to the 2013 experience. Existing FAST Search Center sites can continue to work in 2010 mode after upgrade. If you want the new functionality, you must create new Enterprise Search Center sites in 2013 mode.

-During an upgrade from the server products in the Office 2007 release to SharePoint 2010 Products, you could allow site owners to use Visual Upgrade to keep sites in the old experience on the upgraded environment. When you upgrade to SharePoint 2013, all sites that are still in the old experience in SharePoint 2010 Products are automatically upgraded to the 2010 experience. If you want the opportunity to address any issues and review the sites before they are switched to the new experience, upgrade them to the new experience in your SharePoint 2010 Products environment and review them before you upgrade them to SharePoint 2013. We recommend that you finish visual upgrades before you upgrade to SharePoint 2013. Finishing visual upgrades before you upgrade provides the following benefits:

- - Administrators group on the server on which you are running the PowerShell cmdlets.

- > If you do not have permissions, contact your Setup administrator or SQL Server administrator to request permissions. For additional information about PowerShell permissions, see [Add-SPShellAdmin](/powershell/module/sharepoint-server/Add-SPShellAdmin).

- - [Databaserepair: Stsadm operation](/previous-versions/office/sharepoint-2007-products-and-technologies/cc263282(v=office.12))

- - [Forcedeletelist: Stsadm operation](/previous-versions/office/sharepoint-2007-products-and-technologies/cc262609(v=office.12))

- Make sure that site collections exist in only one content database. Occasionally, site collections can leave behind duplicate or orphaned references in old content databases if they are moved to new databases, or if a copy of a database was attached to the farm, or if there was an error when a site collection was provisioned. If a site collection is referenced in more than one content database or there is more than one instance of the site collection in a content database, it can cause issues when you upgrade by using the database attach upgrade method. If you upgrade a duplicate version of the site collection first, the site map in your configuration database might end up pointing to that version of the site instead of the current version.

- Before you upgrade, use the **Enumallwebs** operation in stsadm command-line tool to discover which sites are in which content databases and compare the results. Also, examine each site collection in the results and check whether it is listed as missing in the site map. Being listed as missing indicates that it is an orphaned site. For more information, see [Enumallwebs: Stsadm operation](/previous-versions/office/sharepoint-2007-products-and-technologies/dd789634(v=office.12)). If you find duplicate or orphaned sites, you can use the **Remove-SPSite** cmdlet in PowerShell to remove the duplicate or orphaned sites from the database.

-[Best practices for upgrading from SharePoint 2010 to SharePoint 2013](best-practices-for-upgrading-from-sharepoint-2010-to-sharepoint-2013.md)

-If you have extensively customized your sites based on SharePoint 2010 Products, you must determine how you want to handle your customizations when you upgrade to SharePoint 2013. Your approach will vary based on the extent of the customizations, the kind of customization, the complexity of your site, and your goals for upgrading. Before you upgrade, you must identify and then evaluate the customizations in your environment and determine whether you will upgrade them, and how.

-After you have identified the customizations, think about the potential upgrade effect of each one. The following table describes types of customizations and the kind of effect they can have during upgrade.

-|**Category of customization**|**Types of customizations**|**Potential effect on upgrade**|

-|Visually-affecting <br/> |Master pages <br/> Themes <br/> Web Pages <br/> Web Parts <br/> Custom JavaScript <br/> Custom CSS files <br/> |Should not affect database upgrade. <br/> For site upgrades: likely to work well in 2010 mode, but need changes to work in 2013 mode. <br/> Test carefully in both modes. <br/> |

- - Does it do something that you cannot do with standard features in the product?

- - Is it a supported kind of customization, or does it introduce risk into your environment?

-|Site definition <br/> |Migrate sites to a supported, predefined site definition, then apply custom features by using solution deployment. <br/> You can also continue to use a custom site definition. You do not have to create a new site definition that is based on SharePoint 2013. <br/> However, if you must perform custom upgrade actions for the definition, you might have to create an upgrade definition file for that site definition. For more information, see [Upgrade Definition Files](/previous-versions/office/developer/sharepoint-2010/ms439232(v=office.14)) on MSDN. <br/> |

-|"Fabulous 40" application templates <br/> |Microsoft is not creating new versions of these templates. Environments that contain sites based on these templates can be upgraded as long as the templates are installed. But there might be issues when you try to upgrade the site collections. Make sure that you test each site before you upgrade the production environment. For more information, see [Troubleshoot database upgrade issues in SharePoint 2013](/previous-versions/office/sharepoint-server-2010/cc262967(v=office.14)). <br/> |

-|Feature <br/> |Evaluate, then redesign or redeploy if it is necessary. <br/> |

-|Workflows and server controls <br/> |Depends on the solution. Contact the vendor to discover whether there is an updated solution. If a workflow is compatible with the new version, redeploy. <br/> |

-|Event handler <br/> |Most event handlers will continue to work without changes. However, if the code for the event handler makes calls to APIs which were deprecated, you will have to rewrite it, and then redeploy it as a feature. <br/> |

-|Managed paths (inclusions/exclusions) <br/> |Re-create inclusions to make sure that you can access all site collections under those paths. <br/> Exclusions were not used in SharePoint 2010 Products. If you had any remaining from an earlier version, they do not have to be re-created. <br/> |

-|Web Parts <br/> |Test to determine whether any actions are required. You might have to adjust the Web Parts to work with strict XHMTL mode. <br/> Test to verify that there have not been changes to any object models or Web services that you call from the Web Part. <br/> If a Web Part is located on a page but not in a Web Part Zone (so that it is, basically, HTML code embedded directly in a page), it will not work if you reset the page to the default template. There is a site collection health rule that will identify files in this status inside a site collection. There is a link from that rule to the page where they can reset to template. <br/> |

-|Custom search solutions that use SQL syntax <br/> |Rework to use FQL syntax and KQL syntax. <br/> Custom search solutions in SharePoint 2013 do not support [SQL syntax](/previous-versions/office/developer/sharepoint-2010/ee558869(v=office.14)). Search in SharePoint 2013 supports FQL syntax and KQL syntax for custom search solutions. You cannot use SQL syntax in custom search solutions using any technologies. This includes the query server object model, the client object model, and the Search REST service. Custom search solutions that use SQL syntax with the index server object model and the Query web service that were created in SharePoint Server 2010 will not work when you upgrade them to SharePoint 2013. Queries submitted via these applications will return an error. For more information about how to use FQL syntax and KQL syntax, see [Keyword Query Language (KQL) syntax reference](/sharepoint/dev/general-development/keyword-query-language-kql-syntax-reference) and [FAST Query Language (FQL) syntax reference](/sharepoint/dev/general-development/fast-query-language-fql-syntax-reference). <br/> |

-While you are reviewing customizations in your environment, you should also make sure that the environment is not using any features or elements that are deprecated. For example, Web Analytics from SharePoint 2010 Products are not available in SharePoint 2013 and you should turn them off before upgrading. Also, SQL Server Search queries are not available in SharePoint 2013. For more information, see [Changes from SharePoint 2010 to SharePoint 2013](/previous-versions/office/sharepoint-server-2010/ff607742(v=office.14)).

-|**Deployment method**|**Recommendation**|

-|Customizations deployed as MSI files <br/> |Contact the vendor for updated files. Most likely, you will have to get a replacement file compatible with SharePoint 2013. <br/> |

-|Solution packages <br/> |Deploy to SharePoint 2013 again. Make sure that you deploy it to the appropriate directory (/14 or /15), depending on the version. <br/> Note that you can no longer add partial trust solution packages to the \bin directory. Any files deployed to the \bin directory must be full trust. Be sure to test any such solutions to make sure that deploying them in full trust does not introduce security vulnerabilities. Also, update any deployment scripts to make sure that they specify the correct trust level. <br/> For more information, see [Install-SPSolution](/powershell/module/sharepoint-server/Install-SPSolution?view=sharepoint-ps&preserve-view=true). <br/> |

-The following kinds of customizations are not supported. If you have any of these customizations in your environment, you must replace them by using a supported kind of customization before you can upgrade. Otherwise, you might experience upgrade issues that cannot be fixed:

- > Some predefined file types ΓÇö such as document icons or actions ΓÇö can be carried forward in a supportable way, although this does not occur automatically. Do not copy over the old version files as that can cause other issues, instead, make the same changes to the new version file Modifications to other predefined files, such as server-side ASPX pages, will be lost during upgrade if you reset to the site template or if you don't make the same changes in the new version files. Depending on the files that were changed and the extent of these changes, the upgrade experience can vary significantly.

-[Deploy custom features to upgraded site collections in SharePoint Server 2013](./deploy-custom-features-to-upgraded-site-collections-in-sharepoint-server-2013.md)

-The following table lists the techniques that you can use during upgrade to reduce the time that users cannot access their content or to potentially increase upgrade performance.

-|**Case**|**Upgrade approach**|

-|Upgrading an environment that uses forms-based authentication? <br/> |Additional steps are required to upgrade when you are using forms-based authentication. For more information, see [Configure forms-based authentication for a claims-based web application in SharePoint Server](/previous-versions/office/sharepoint-server-2010/ee806890(v=office.14)). <br/> |

-|Upgrading very large databases? <br/> |In general, very large databases ΓÇö especially databases that have a large number or large size of document versions inside them ΓÇö take longer to upgrade than smaller databases. However, the complexity of the data determines how long it takes to upgrade, not the size of the database itself. If the upgrade process times out, it is usually because of connection issues. For more information about how long upgrade might take for your environment, see [Plan for performance during upgrade to SharePoint 2013](/previous-versions/office/sharepoint-server-2010/cc262891(v=office.14)). <br/> |

-|Changing languages? <br/> | You have two choices, depending on whether a single site or your whole environment is changing languages: <br/> To change the multiple user interface (MUI) language for a specific site, upgrade in the same language, and then install the new language pack and change to that language. <br/> > [!CAUTION]> You must have the appropriate language packs installed to upgrade any sites based on a localized site definition. If you do not have the new language pack, the sites will not be available. Wait for the new language packs to be released before you try to upgrade those sites. To change the installation language for your environment, set up your new environment in the new language, and then attach and upgrade your databases in the new language. <br/> |

-