Set Site Collection to ReadOnly

Two ways to set a site collection to readonly:

1. Central Admin --> Application Management --> Site Collections --> Configure Quotas and Locks --> Select Site Collection --> Select ReadOnly
2. Via PowerShell:
   

   Set-SPSite -Identity "site_collection_url" -LockState "ReadOnly"
   

LockState options:

• Unlock to unlock the site collection and make it available to users.
• NoAdditions to prevent users from adding new content to the site collection. Updates and deletions are still allowed.
• ReadOnly to prevent users from adding, updating, or deleting content.
• NoAccess to prevent users from accessing the site collection and its content. Users who attempt to access the site receive an error.