Activate a feature in all the SharePoint site collections-PowerShell

$webAppUrl = "Web Application URL"
 
$webapp = Get-SPWebApplication $webAppUrl  | Get-SPSite -Limit All | Get-SPSite -limit 

all | ForEach-Object {Enable-SPFeature -Identity 'Feature guid'  -Url $_.Url}

Making a Web Part Safe by Default

If you have a Web Part and want to make it safe anyway, you can add this information to the solution package, as shown in the following code.

<Solution SolutionId="{2E9DDE85-8822–42EC-3a92–E85537810BAA}"

xmlns="http://schemas.microsoft.com/sharepoint/">

<FeatureManifests />

<ApplicationResourceFiles />

<CodeAccessSecurity />

<DwpFiles />

<Resources />

<RootFiles />

<SiteDefinitionManifests />

<TemplateFiles />

<Assemblies>

<Assembly DeploymentTarget="WebApplication" Location="Apress.WebParts.dll">

<SafeControls>

<SafeControl Assembly="Apress.WebPart, Version=1.0.0.0, Culture=neutral,

PublicKeyToken=a05eff78260564"

Namespace="Apress" TypeName="*" Safe="True"/>

</SafeControls>

</Assembly>

</Assemblies>

</Solution>

This technique is limited to your own Web Parts, where you have control over the packaging process. But it’s the safest way to add controls to web.config.