How to fix Error 3423 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 3423

Why This Error Happens

Error 3423 typically appears as an informational message indicating that the SQL Server instance started in multiuser mode rather than single-user mode, which usually occurs after a database recovery operation or maintenance task was expected to run in a restricted state. This can happen when startup parameters (like -m) were not applied correctly, when a previous single-user session was not properly closed, or when configuration changes made during a restore/recovery process were overridden by default service startup settings. In some cases, this message surfaces because a scheduled task, Group Policy, or failover cluster resource manager restarted the SQL Server service without preserving the intended startup flags.

Step-by-Step Resolution Guide

Step 1: Verify Current Startup Parameters

  • Open SQL Server Configuration Manager on Windows Server 2025 / Windows 11.
  • Navigate to SQL Server Services > right-click your instance > Properties > Startup Parameters tab.
  • Check whether -m (single-user mode) is present if it was intended for maintenance tasks.
  • Confirm the parameter order and syntax: -d, -l, -e paths should not be malformed.

Step 2: Correct the Startup Mode Configuration

  • If single-user mode was required for a specific task (e.g., restoring master database), add the parameter manually:
  • -m"SQLCMD" (restricts access to a single application/user)
  • Restart the SQL Server service via:
  net stop MSSQLSERVER
  net start MSSQLSERVER
  • If multiuser mode is actually the desired state, no action is needed — document the message as informational only.

Step 3: Check for Conflicting Services or Scripts

  • Review Task Scheduler and Windows Services (services.msc) for any automated scripts that restart the SQL Server service outside of maintenance windows.
  • Inspect SQL Server Error Log at:
  C:\Program Files\Microsoft SQL Server\MSSQL17.MSSQLSERVER\MSSQL\Log\ERRORLOG
  • Look for entries immediately before Error 3423 to identify what triggered the restart.

Step 4: Validate Cluster or Always On Availability Group Settings (If Applicable)

  • If running on a Windows Server Failover Cluster (WSFC), open Failover Cluster Manager.
  • Confirm the SQL Server resource’s startup parameters match the intended configuration under Resource Properties > Properties tab.
  • Ensure no conflicting resource dependencies are forcing a service restart in multiuser mode unexpectedly.

Alternative or Verification Steps

  • Run SELECT SERVERPROPERTY('IsSingleUser'); in SSMS — a result of 0 confirms the instance is correctly in multiuser mode.
  • If the message persists unexpectedly, review the Windows Event Viewer (Application Log) for correlating Service Control Manager events that may indicate an external restart trigger.