RUNAS.exe

Execute a program under a different user account (non-elevated).

Syntax
      RUNAS [ [/noprofile | /profile] [/env] [/savecred | /netonly] ]
         /user:UserName program

      RUNAS [ [/noprofile | /profile] [/env] [/savecred] ]
         /smartcard [/user:UserName] program

      Display the trust levels that can be used:
      RUNAS /showtrustlevels

      Run a program at a given TrustLevel:
      RUNAS /trustlevel:TrustLevel program

Key
   /noprofile       Do not load the user’s profile.
                    This causes the application to load more quickly, but
                    can cause some applications to malfunction.

   /profile         Load the user’s profile. (default)

   /env             Use the current environment instead of user’s.

   /netonly         Use the credentials for remote access only.

   /savecred        Use credentials previously saved by the user.

   /smartcard       Load the credentials from a smartcard.

   /user            UserName in the form USER@DOMAIN or DOMAIN\USER

   /trustlevel Level  One of levels enumerated in /showtrustlevels.
                      RunAs is not able to launch an application with an elevated
                      access token.

   program          The program to run.

Enter the password when prompted. The RunAs program demands that you type the password manually. This was a conscious design decision. If it were possible to pass the password on the command line, people would start embedding passwords into batch files and logon scripts, which is laughably insecure. [via Raymond Chen]

/profile is not compatible with /netonly.
/savecred is not compatible with /smartcard.

When you start a program with RunAs /netonly, the program will execute on your local computer as the user you are currently logged on as, but any connections to other computers on the network will be made using the user account specified.

Without /netonly everything will run under the user account specified.

The RUNAS command unlike most other CMD and DOS commands requires that it’s command line is quoted, it uses the regular C runtime library command line parser. This also means that RUNAS requires the backslash \ as an escape character, not the standard ^ escape used by other CMD commands.

RunAs Reqires the "Secondary Logon" service to be running.

The error level %ERRORLEVEL% returned by RunAs: success = 0, failure = 1

Run with Elevated permissions

In Windows Vista and above, you can run a script with elevated permissions by right clicking and choosing "Run As Administrator"

The RunAs command predates elevation, so it has no switch for running an elevated command.
Alternatives: invoke the UAC dialogue by calling the VBScript function .ShellExecute
or call PowerShell.exe -Verb runAs

If you are already running elevated, for example an elevated CMD shell, then RUNAS will launch an application as elevated, but this is equally true just running a command without RUNAS, it makes no difference.

When a script is run with elevated permissions several aspects of the user environment will change: The current directory, the current TEMP folder and any mapped drives will be disconnected.

RunAs from Windows Explorer

Select an executable file, Shift-Right-click and select Run As..
This option can be hidden by setting
HKLM\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer
HideRunAsVerb=1

RunAs to force a password Sync

If you are connecting to a remote network/VPN and the remote/domain password gets out of sync with the local machine, use RunAs to open a second prompt explicitly passing the domain and username to force a password sync.

• runas /user:SS64Dom\User64 cmd.exe
• Enter the domain password.
• Wait a few minutes until you see the notification area pop-up: "Windows Needs Your Current Credentials Please lock this computer, then unlock it using your most recent password or smart card.

Examples

Run notepad.exe as the user Jdoe on domain SS64dom with no profile:

C:\> runas.exe /noprofile /user:SS64Dom\jDoe "notepad.exe"

Run CMD.exe as the Administrator on the local machine Dellpc64:

C:\> runas /profile /user:DELLPC64\administrator CMD

or this can be written:
C:\> runas /profile /user:.\administrator CMD

Run CMD.exe as the current user on domain SS64dom, this will re-authenticate, refreshing any group permissions before running CMD.exe:

C:\> runas /profile /user:SS64Dom\%username% CMD.exe

Run Notepad.exe as 'Natasha' on domain SS64dom using the current environment, and open a file, escape the quote characters around the filename with \ :

C:\> runas /profile /env /user:SS64Dom\natasha "notepad \"C:\work\demo file.txt\""

Run Active Directory Users and Computers (dsa.msc) as the user Jdoe on domain SS64dom:

C:\> runas /env /user:SS64Dom\jDoe "START %windir%\system32\dsa.msc"

“He who reigns within himself, and rules passions, desires, and fears, is more than a king” ~ Milton

Related commands

PsExec - Execute process remotely.
ShellRunAs - Run a command under a different user account.
START - Start a program, command or batch file.
How-to: Run with elevated permissions
How-to: Logon Types - Windows Logon types.
Aaron Margosis - Running with least privilege.
joeware.net - CPAU (Create Process As User) like RunAs but with an options to encrypt the password.
PowerShell: Run As Admin / elevation
Equivalent bash command (Linux): SU - Switch User.