About Jobs

SHORT DESCRIPTION

Provides information about how PowerShell background jobs run a command or expression in the background without interacting with the current session.

LONG DESCRIPTION

This topic explains how to run background jobs in PowerShell on a local computer. For information about running background jobs on remote computers, see about_Remote_Jobs.

When you start a background job, the command prompt returns immediately, even if the job takes an extended time to complete. You can continue to work in the session without interruption while the job runs.

THE JOB CMDLETS

Cmdlet Description
Start-Job Starts a background job on a local computer.
Get-Job Gets the background jobs that were started in the
current session.
Receive-Job Gets the results of background jobs.
Stop-Job Stops a background job.
Wait-Job Suppresses the command prompt until one or all jobs are
complete.
Remove-Job Deletes a background job.
Invoke-Command The AsJob parameter runs any command as a background
job on a remote computer. You can also use
Invoke-Command to run any job command remotely,
including a Start-Job command.

HOW TO START A JOB ON THE LOCAL COMPUTER

To start a background job on the local computer, use the Start-Job cmdlet.

To write a Start-Job command, enclose the command that the job runs in braces ( { } ). Use the ScriptBlock parameter to specify the command.

The following command starts a background job that runs a Get-Process command on the local computer.

Start-Job -ScriptBlock {Get-Process}

The Start-Job command returns an object that represents the job. The job object contains useful information about the job, but it does not contain the job results.

Save the job object in a variable, and then use it with the other Job cmdlets to manage the background job. The following command starts a job object and saves the resulting job object in the $job variable.

$job = Start-Job -ScriptBlock {Get-Process}

You can also use & to start jobs. The following command is functionally equivalent to the command above.

$job = Get-Process &

The & is called the ampersand background operator. For more information on the ampersand background operator, see ampersand background operator.

You can also use the Get-Job cmdlet to get objects that represent the jobs started in the current session. Get-Job returns the same job object that Start-Job returns.

GETTING JOB OBJECTS

To get object that represent the background jobs that were started in the current session, use the Get-Job cmdlet. Without parameters, Get-Job returns all of the jobs that were started in the current session.

For example, the following command gets the jobs in the current session.

PS C:> Get-Job

Id  Name  PSJobTypeName State      HasMoreData  Location   Command
--  ----  ------------- -----      -----------  --------   -------
1   Job1  BackgroundJob Running    True         localhost  Get-Process

You can also save the job object in a variable and use it to represent the job in a later command. The following command gets the job with ID 1 and saves it in the $job variable.

$job = Get-Job -Id 1

The job object contains the state of the job, which indicates whether the job has finished. A finished job has a state of "Complete" or "Failed". A job might also be blocked or running.

Get-Job

Id  Name  PSJobTypeName State      HasMoreData  Location   Command
--  ----  ------------- -----      -----------  --------   -------
1   Job1  BackgroundJob Complete   True         localhost  Get-Process

GETTING THE RESULTS OF A JOB

When you run a background job, the results do not appear immediately. Instead, the Start-Job cmdlet returns a job object that represents the job, but it does not contain the results. To get the results of a background job, use the Receive-Job cmdlet.

The following command uses the Receive-Job cmdlet to get the results of the job. It uses a job object saved in the $job variable to identify the job.

Receive-Job -Job $job

The Receive-Job cmdlet returns the results of the job.

Handles  NPM(K)    PM(K)      WS(K) VM(M)   CPU(s)    Id ProcessName
-------  ------    -----      ----- -----   ------    -- -----------
    103       4    11328       9692    56           1176 audiodg
    804      14    12228      14108   100   101.74  1740 CcmExec
    668       7     2672       6168   104    32.26   488 csrss
# ...

You can also save the results of a job in a variable. The following command saves the results of the job in the $job variable to the $results variable.

$results = Receive-Job -Job $job

And, you can save the results of the job in a file by using the redirection operator (>) or the Out-File cmdlet. The following command uses the redirection operator to save the results of the job in the $job variable in the Results.txt file.

Receive-Job -Job $job > results.txt

GETTING AND KEEPING PARTIAL JOB RESULTS

The Receive-Job cmdlet gets the results of a background job. If the job is complete, Receive-Job gets all job results. If the job is still running, Receive-Job gets the results that have been generated thus far. You can run Receive-Job commands again to get the remaining results.

When Receive-Job returns results, by default, it deletes those results from the cache where job results are stored. If you run another Receive-Job command, you get only the results that are not yet received.

The following commands show the results of Receive-Job commands run before the job is complete.

C:\PS> Receive-Job -Job $job

Handles  NPM(K)    PM(K)      WS(K) VM(M)   CPU(s)     Id ProcessName
-------  ------    -----      ----- -----   ------     -- -----------
    103       4    11328       9692    56            1176 audiodg
    804      14    12228      14108   100   101.74   1740 CcmExec

C:\PS> Receive-Job -Job $job

Handles  NPM(K)    PM(K)      WS(K) VM(M)   CPU(s)     Id ProcessName
-------  ------    -----      ----- -----   ------     -- -----------
    68       3     2632        664    29     0.36   1388 ccmsetup
   749      22    21468      19940   203   122.13   3644 communicator
   905       7     2980       2628    34   197.97    424 csrss
  1121      25    28408      32940   174   430.14   3048 explorer

To prevent Receive-Job from deleting the job results that it has returned, use the Keep parameter. As a result, Receive-Job returns all of the results that have been generated until that time.

The following commands show the effect of using the Keep parameter on a job that is not yet complete.

C:\PS> Receive-Job -Job $job -Keep

Handles  NPM(K)    PM(K)      WS(K) VM(M)   CPU(s)     Id ProcessName
-------  ------    -----      ----- -----   ------     -- -----------
    103       4    11328       9692    56            1176 audiodg
    804      14    12228      14108   100   101.74   1740 CcmExec

C:\PS> Receive-Job -Job $job -Keep

Handles  NPM(K)    PM(K)      WS(K) VM(M)   CPU(s)     Id ProcessName
-------  ------    -----      ----- -----   ------     -- -----------
    103       4    11328       9692    56            1176 audiodg
    804      14    12228      14108   100   101.74   1740 CcmExec
     68       3     2632        664    29     0.36   1388 ccmsetup
    749      22    21468      19940   203   122.13   3644 communicator
    905       7     2980       2628    34   197.97    424 csrss
   1121      25    28408      32940   174   430.14   3048 explorer

WAITING FOR THE RESULTS

If you run a command that takes a long time to complete, you can use the properties of the job object to determine when the job is complete. The following command uses the Get-Job object to get all of the background jobs in the current session.

Get-Job

The results appear in a table. The status of the job appears in the State column.

Id Name  PSJobTypeName State    HasMoreData Location  Command
-- ----  ------------- -----    ----------- --------  -------
1  Job1  BackgroundJob Complete True        localhost Get-Process
2  Job2  BackgroundJob Running  True        localhost Get-EventLog -Log ...
3  Job3  BackgroundJob Complete True        localhost dir -Path C:\* -Re...

In this case, the State property reveals that Job 2 is still running. If you were to use the Receive-Job cmdlet to get the job results now, the results would be incomplete. You can use the Receive-Job cmdlet repeatedly to get all of the results. By default, each time you use it, you get only the results that were not already received, but you can use the Keep parameter of the Receive-Job cmdlet to retain the results, even though they were already received.

You can write the partial results to a file and then append newer results as they arrive or you can wait and check the state of the job later.

You can use the Wait parameter of the Receive-Job cmdlet, which does not return the command prompt until the job is complete and all results are available.

You can also use the Wait-Job cmdlet to wait for any or all of the results of the job. Wait-Job lets you wait for a particular job, for all jobs, or for any of the jobs to be completed.

The following command uses the Wait-Job cmdlet to wait for a job with ID 10.

Wait-Job -ID 10

As a result, the PowerShell prompt is suppressed until the job is completed.

You can also wait for a predetermined period of time. This command uses the Timeout parameter to limit the wait to 120 seconds. When the time expires, the command prompt returns, but the job continues to run in the background.

Wait-Job -ID 10 -Timeout 120

STOPPING A JOB

To stop a background job, use the Stop-Job cmdlet. The following command starts a job to get every entry in the System event log. It saves the job object in the $job variable.

$job = Start-Job -ScriptBlock {Get-EventLog -Log System}

The following command stops the job. It uses a pipeline operator (|) to send the job in the $job variable to Stop-Job.

$job | Stop-Job

DELETING A JOB

To delete a background job, use the Remove-Job cmdlet. The following command deletes the job in the $job variable.

Remove-Job -Job $job

INVESTIGATING A FAILED JOB

To find out why a job failed, use the Reason subproperty of the job object.

The following command starts a job without the required credentials. It saves the job object in the $job variable.

$job = Start-Job -ScriptBlock {New-Item -Path HKLM:\Software\MyCompany}

Id Name  PSJobTypeName State  HasMoreData  Location  Command
-- ----  ------------- -----  -----------  --------  -------
1  Job1  BackgroundJob Failed False        localhost New-Item -Path HKLM:...

The following command uses the Reason property to find the error that caused the job to fail.

$job.ChildJobs[0].JobStateInfo.Reason

In this case, the job failed because the remote computer required explicit credentials to run the command. The value of the Reason property is:

Connecting to remote server failed with the following error message : Access is denied.

SEE ALSO

about_Remote_Jobs

about_Job_Details

about_Remote

about_PSSessions

Start-Job

Get-Job

Receive-Job

Stop-Job

Wait-Job

Remove-Job

Invoke-Command