about_PSSession_Details

Artikel
12/13/2022

Short description

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

Long description

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

Unlike the sessions that 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, 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 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 PowerShell runs. Each session includes an instance of the System.Management.Automation engine and a host program in which PowerShell runs. The host can be the familiar PowerShell console or another program that runs commands, such as Cmd.exe, or a program built to host 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 PowerShell. And, PowerShell creates temporary sessions to run individual commands. However, you can also create sessions (called "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, 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, 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 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 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 on Windows computers 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.

On a Windows computer, 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 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 Windows computer.

For more information, see about_Remote_Disconnected_Sessions.

What Happens to My PSSession if 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, PowerShell attempts to recover active PSSessions that are disconnected unintentionally, such as by a computer reboot, a temporary power outage or network disruption. 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, PowerShell attempts to maintain the PSSession on the remote computer. However, if no commands are running in the PSSession, PowerShell closes the PSSession when the connected session closes.

For more information, see about_Remote_Disconnected_Sessions.

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, 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.

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