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about_PSSession_Details

Updated: May 8, 2014

Applies To: Windows PowerShell 2.0, Windows PowerShell 3.0, Windows PowerShell 4.0

TOPIC
    about_PSSession_Details

SHORT DESCRIPTION
    Provides detailed information about Windows PowerShell sessions and the 
    role they play in remote commands.

LONG DESCRIPTION
    A session is an environment in which Windows PowerShell runs. A session is 
    created for you whenever you start Windows PowerShell. You can create 
    additional sessions, called "Windows PowerShell sessions" or "PSSessions" 
    on your computer or another computer.

    Unlike the sessions that Windows PowerShell creates for you, you control 
    and manage the PSSessions that you create.

    PSSessions play an important role in remote computing. When you create a 
    PSSession that is connected to a remote computer, Windows PowerShell 
    establishes a persistent connection to the remote computer to support the 
    PSSession. You can use the PSSession to run a series of commands, 
    functions, and scripts that share data. 

    This topic provides detailed information about sessions and PSSessions
    in Windows PowerShell. For basic information about the tasks that you
    can perform with sessions, see about_PSSessions.   

  ABOUT SESSIONS

    Technically, a session is an execution environment in which Windows 
    PowerShell runs. Each session includes an instance of the 
    System.Management.Automation engine and a host program in which Windows
    PowerShell runs. The host can be the familiar Windows PowerShell console
    or another program that runs commands, such as Cmd.exe, or a program built
    to host Windows PowerShell, such as Windows PowerShell Integrated Scripting
    Environment (ISE). From a Windows perspective, a session is a Windows 
    process on the target computer. 

    Each session is configured independently. It includes its own properties, 
    its own execution policy, and its own profiles. The environment that exists 
    when the session is created persists for its lifetime even if you change 
    the environment on the computer. All sessions are created in a global 
    scope, even sessions that you create in a script. 

    You can run only one command (or command pipeline) in a session at one 
    time. A second command run synchronously (one at a time) waits up to four 
    minutes for the first command to be completed. A second command run
    asynchronously (concurrently) fails.

  ABOUT PSSESSIONS

    A session is created each time that you start Windows PowerShell. And, 
    Windows PowerShell creates temporary sessions to run individual commands. 
    However, you can also create sessions (called "Windows PowerShell sessions" 
    or "PSSessions") that you control and manage.
 
    PSSessions are critical to remote commands. If you use the ComputerName
    parameter of the Invoke-Command or Enter-PSSession cmdlets, Windows
    PowerShell establishes a temporary session to run the command and then
    closes the session as soon as the command or the interactive session
    is complete. 

    However, if you use the New-PSSession cmdlet to create a PSSession, Windows
    PowerShell establishes a persistent session on the remote computer in which
    you can run multiple commands or interactive sessions. The PSSessions that 
    you create remain open and available for use until you delete them or until
    you close the session in which they were created.

    When you create a PSSession on a remote computer, the system creates a
    PowerShell process on the remote computer and establishes a connection
    from the local computer to the process on the remote computer. When you
    create a PSSession on the local computer, both the new process and the
    connections are created on the local computer.


  WHEN DO I NEED A PSSESSION?

    The Invoke-Command and Enter-PSSession cmdlets have both ComputerName and
    Session parameters. You can use either to run a remote command. 

    Use the ComputerName parameter to run a single command or a series of
    unrelated commands on one or many computers. 

    To run commands that share data, you need a persistent connection to the 
    remote computer. In that case, create a PSSession, and then use the Session 
    parameter to run commands in the PSSession.

    Many other cmdlets that get data from remote computers, such as 
    Get-Process, Get-Service, Get-EventLog, and Get-WmiObject have only a 
    ComputerName parameter. They use technologies other than Windows PowerShell 
    remoting to gather data remotely. These cmdlets do not have a Session 
    parameter, but you can use the Invoke-Command cmdlet to run these commands 
    in a PSSession.
 

  HOW DO I CREATE A PSSESSION?

    To create a PSSession, use the New-PSSession cmdlet. You can use
    New-PSSession to create a PSSession on a local or remote computer.


  CAN I CREATE A PSSESSION ON ANY COMPUTER?
 
    To create a PSSession that is connected to a remote computer, the computer 
    must be configured for remoting in Windows PowerShell. The current user 
    must be a member of the Administrators group on the remote computer, or
    the current user must be able to supply the credentials of a member of 
    the Administrators group. For more information, 
    see about_Remote_Requirements.


  CAN I SEE MY PSSESSIONS IN OTHER SESSIONS?

    Beginning in Windows PowerShell 3.0, the ComputerName 
    parameter of the Get-PSSession cmdlet gets PSSessions
    that you created on the specified remote computers. 

    Active PSSessions are maintained on the remote computer
    (the "server-side" of a connection) and you can get them
    from any session on any computer. 

    For example, if you create a PSSession from the Server01
    computer to the Server02 computer, and then switch to the
    Server03 computer, you can use a command like the following
    one to get the session.

      Get-PSSession -ComputerName Server02

    Even if you disconnect from the session, the session is
    maintained on the remote computer until you delete it or it
    times out.

    In Windows PowerShell 2.0, you can get only the PSSessions 
    that you have created in the current session. You cannot get
    PSSessions that you created in other sessions.

    For more information, see Get-PSSession.


  CAN I SEE THE PSSESSIONS THAT OTHERS HAVE CREATED ON MY COMPUTER?

    You can get and manage only the PSSessions that others have created
    only if you can supply the credentials of the user who created the
    PSSession or the session configuration that the PSSession uses 
    includes RunAs credentials. Otherwise, you can get, connect to, use,
    and manage only the PSSessions that you created.


  CAN I CONNECT TO A PSSESSION FROM A DIFFERENT COMPUTER?

    Beginning in Windows PowerShell 3.0, PSSessions are independent
    of the sessions in which they were created. Active PSSessions
    are maintained on the computer at the remote or "server-side" of
    a connection. 

    You can use the Disconnect-PSSession cmdlet to disconnect 
    from a PSSession. The PSSession is disconnected from the 
    local session, but is maintained on the remote computer.
    Commands continue to run in the disconnected PSSession. You 
    can close Windows PowerShell and shut down the originating computer
    without interrupting the PSSession. 

    Then, even hours later, you can use the Get-PSSession cmdlet to
    get the PSSession and the Connect-PSSession cmdlet to connect to the
    PSSession from a new session on a different computer.

    For more information, see about_Remote_Disconnected_Sessions
    (http://go.microsoft.com/fwlink/?LinkID=252847).


  WHAT HAPPENS TO MY PSSESSION IF I MY COMPUTER STOPS?
    Disconnected PSSessions are independent of the sessions
    in which they were created. If you disconnect a PSSession
    and then close the originating computer, the PSSession is
    maintained on the remote computer.

    In addition, Windows PowerShell attempts to recover active
    PSSessions that are disconnected unintentionally, such as
    by a computer reboot, a temporary power outage or network
    disruption. Windows PowerShell attempts to maintain or recover
    the PSSession to an Opened state, if the originating session
    is still available, or to a disconnected state if it is not.
    
    An "active" PSSession is one that is running commands. If
    a PSSession is connected (not disconnected) and commands are
    running in the PSSession when the connected session closes, 
    Windows PowerShell attempts to maintain the PSSession on the
    remote computer. However, if no commands are running in the 
    PSSession, Windows PowerShell closes the PSSession when the
    connected session closes.

    For more information, see about_Remote_Disconnected_Sessions
    (http://go.microsoft.com/fwlink/?LinkID=252847).



  CAN I RUN A BACKGROUND JOB IN A PSSESSION?

    Yes. A background job is a command that runs asynchronously in the 
    background without interacting with the current session. When you submit 
    a command to start a job, the command returns a job object, but the job 
    continues to run in the background until it is complete.

    To start a background job on a local computer, use the Start-Job command. 
    You can run the background job in a temporary connection (by using the 
    ComputerName parameter) or in a PSSession (by using the Session parameter). 

    To start a background job on a remote computer, use the Invoke-Command 
    cmdlet with its AsJob parameter, or use the Invoke-Command cmdlet to run a 
    Start-Job command on a remote computer. When using the AsJob parameter, 
    you can use the ComputerName or Session parameters.

    When using Invoke-Command to run a Start-Job command, you must run the
    command in a PSSession. If you use the ComputerName parameter, Windows 
    PowerShell ends the connection when the job object returns, and the job is 
    interrupted.

    For more information, see about_Jobs.


  CAN I RUN AN INTERACTIVE SESSION?

    Yes. To start an interactive session with a remote computer, use the
    Enter-PSSession cmdlet. In an interactive session, the commands that you
    type run on the remote computer, just as if you typed them directly on the
    remote computer. 

    You can run an interactive session in a temporary session (by using the 
    ComputerName parameter) or in a PSSession (by using the Session parameter). 
    If you use a PSSession, the PSSession retains the data from previous 
    commands, and the PSSession retains any data generated during the 
    interactive session for use in later commands.

    When you end the interactive session, the PSSession remains open and 
    available for use.

    For more information, see Enter-PSSession and Exit-PSSession.
 

  MUST I DELETE THE PSSESSIONS?

    Yes. A PSSession is a process, which is a self-contained environment that 
    uses memory and other resources even when you are not using it. When you are 
    finished with a PSSession, delete it. If you create multiple PSSessions, 
    close the ones that you are not using, and maintain only the ones currently 
    in use. 

    To delete PSSessions, use the Remove-PSSession cmdlet. It deletes the 
    PSSessions and releases all of the resources that they were using. 

    You can also use the IdleTimeOut parameter of New-PSSessionOption to close
    an idle PSSession after an interval that you specify. For more information, 
    see New-PSSessionOption.

    If you save a PSSession object in a variable and then delete the PSSession 
    or let it time out, the variable still contains the PSSession object, but 
    the PSSession is not active and cannot be used or repaired.
    

  ARE ALL SESSIONS AND PSSESSIONS ALIKE?

    No. Developers can create custom sessions that include only selected 
    providers and cmdlets. If a command works in one session but not in 
    another, it might be because the session is restricted.


SEE ALSO
    about_Jobs
    about_PSSessions
    about_Remote 
    about_Remote_Disconnected_Sessions
    about_Remote_Requirements
    Invoke-Command
    New-PSSession 
    Get-PSSession 
    Remove-PSSession 
    Enter-PSSession 
    Exit-PSSession



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