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 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.