about_Job_Details
Short description
Provides details about background jobs on local and remote computers.
Detailed description
This topic explains the concept of a background job and provides technical information about how background jobs work in PowerShell.
This topic is a supplement to the about_Jobs, about_Thread_Jobs, and about_Remote_Jobs topics.
About background jobs
A background job runs a command or expression asynchronously. It might run a cmdlet, a function, a script, or any other command-based task. It is designed to run commands that take an extended period of time, but you can use it to run any command in the background.
When a synchronous command runs, the PowerShell command prompt is suppressed until the command is complete. But a background job does not suppress the PowerShell prompt. A command to start a background job returns a job object. The prompt returns immediately so you can work on other tasks while the background job runs.
However, when you start a background job, you do not get the results immediately even if the job runs very quickly. The job object that is returned contains useful information about the job, but it does not contain the job results. You must run a separate command to get the job results. You can also run commands to stop the job, to wait for the job to be completed, and to delete the job.
To make the timing of a background job independent of other commands, each background job runs in its own PowerShell session. However, this can be a temporary connection that is created only to run the job and is then destroyed, or it can be a persistent PSSession that you can use to run several related jobs or commands.
Using the job cmdlets
Use a Start-Job command to start a background job on a local computer.
Start-Job returns a job object. You can also get objects representing the
jobs that were started on the local computer using the Get-Job cmdlet.
To get the job results, use a Receive-Job command. If the job is not
complete, Receive-Job returns partial results. You can also use the
Wait-Job cmdlet to suppress the command prompt until one or all of the jobs
that were started in the session are complete.
To stop a background job, use the Stop-Job cmdlet. To delete a job, use the
Remove-Job cmdlet.
For more information about how the cmdlets work, see the Help topic for each cmdlet, and see about_Jobs.
Starting background jobs on remote computers
You can create and manage background jobs on a local or remote computer. To run
a background job remotely, use the AsJob parameter of a cmdlet such as
Invoke-Command, or use the Invoke-Command cmdlet to run a Start-Job
command remotely. You can also start a background job in an interactive
session.
For more information about remote background jobs, see about_Remote_Jobs.
Child jobs
Each background job consists of a parent job and one or more child jobs. In
jobs started using Start-Job or the AsJob parameter of Invoke-Command,
the parent job is an executive. It does not run any commands or return any
results. The commands are actually run by the child jobs. Jobs started using
other cmdlets might work differently.
The child jobs are stored in the ChildJobs property of the parent job object. The ChildJobs property can contain one or many child job objects. The child job objects have a Name, ID, and InstanceId that differ from the parent job so that you can manage the parent and child jobs individually or as a unit.
To get the parent and child jobs of a job, use the IncludeChildJobs
parameter of the Get-Job cmdlet. The IncludeChildJob parameter was
introduced in Windows PowerShell 3.0.
PS> Get-Job -IncludeChildJob
Id Name PSJobTypeName State HasMoreData Location Command
-- ---- ------------- ----- ----------- -------- -------
1 Job1 RemoteJob Failed True localhost Get-Process
2 Job2 Completed True Server01 Get-Process
3 Job3 Failed False localhost Get-Process
To get the parent job and only the child jobs with a particular State
value, use the ChildJobState parameter of the Get-Job cmdlet. The
ChildJobState parameter was introduced in Windows PowerShell 3.0.
PS> Get-Job -ChildJobState Failed
Id Name PSJobTypeName State HasMoreData Location Command
-- ---- ------------- ----- ----------- -------- -------
1 Job1 RemoteJob Failed True localhost Get-Process
3 Job3 Failed False localhost Get-Process
To get the child jobs of a job on all versions of PowerShell, use the ChildJob property of the parent job.
PS> (Get-Job Job1).ChildJobs
Id Name PSJobTypeName State HasMoreData Location Command
-- ---- ------------- ----- ----------- -------- -------
2 Job2 Completed True Server01 Get-Process
3 Job3 Failed False localhost Get-Process
You can also use a Get-Job command on the child job, as shown in the
following command:
PS> Get-Job Job3
Id Name PSJobTypeName State HasMoreData Location Command
-- ---- ------------- ----- ----------- -------- -------
3 Job3 Failed False localhost Get-Process
The configuration of the child job depends on the command that you use to start the job.
When you use
Start-Jobto start a job on a local computer, the job consists of an executive parent job and a child job that runs the command.When you use the AsJob parameter of
Invoke-Commandto start a job on one or more computers, the job consists of an executive parent job and a child job for each job run on each computer.When you use
Invoke-Commandto run aStart-Jobcommand on one or more remote computers, the result is the same as a local command run on each remote computer. The command returns a job object for each computer. The job object consists of an executive parent job and one child job that runs the command.
The parent job represents all of the child jobs. When you manage a parent job, you also manage the associated child jobs. For example, if you stop a parent job, all child jobs are stopped. If you get the results of a parent job, you get the results of all child jobs.
However, you can also manage child jobs individually. This is most useful when
you want to investigate a problem with a job or get the results of only one of
a number of child jobs started using the AsJob parameter of
Invoke-Command.
The following command uses the AsJob parameter of Invoke-Command to start
background jobs on the local computer and two remote computers. The command
saves the job in the $j variable.
PS> $j = Invoke-Command -ComputerName localhost, Server01, Server02 `
-Command {Get-Date} -AsJob
When you display the Name and ChildJob properties of the job in $j, it
shows that the command returned a job object with three child jobs, one for
each computer.
PS> $j | Format-List Name, ChildJobs
Name : Job3
ChildJobs : {Job4, Job5, Job6}
When you display the parent job, it shows that the job failed.
PS> $j
Id Name PSJobTypeName State HasMoreData Location
-- ---- ------------- ----- ----------- --------
3 Job3 RemotingJob Failed False localhost,Server...
But when you run a Get-Job command that gets the child jobs, the output
shows that only one child job failed.
PS> Get-Job -IncludeChildJobs
Id Name PSJobTypeName State HasMoreData Location Command
-- ---- ------------- ----- ----------- -------- -------
3 Job3 RemotingJob Failed False localhost,Server...
4 Job4 Completed True localhost Get-Date
5 Job5 Failed False Server01 Get-Date
6 Job6 Completed True Server02 Get-Date
To get the results of all child jobs, use the Receive-Job cmdlet to get
the results of the parent job. But you can also get the results of a
particular child job, as shown in the following command.
PS> Receive-Job -Name Job6 -Keep | Format-Table ComputerName,
>> DateTime -AutoSize
ComputerName DateTime
------------ --------
Server02 Thursday, March 13, 2008 4:16:03 PM
The child jobs feature of PowerShell background jobs gives you more control over the jobs that you run.
Job types
PowerShell supports different types of jobs for different tasks. Beginning in Windows PowerShell 3.0, developers can write "job source adapters" that add new job types to PowerShell and include the job source adapters in modules. When you import the module, you can use the new job type in your session.
For example, the PSScheduledJob module adds scheduled jobs and the PSWorkflow module adds workflow jobs.
Custom jobs types might differ significantly from standard PowerShell background jobs. For example, scheduled jobs are saved on disk; they do not exist only in a particular session. Workflow jobs can be suspended and resumed.
The cmdlets that you use to manage custom jobs depend on the job type. For
some, you use the standard job cmdlets, such as Get-Job and Start-Job. Others
come with specialized cmdlets that manage only a particular type of job. For
detailed information about custom job types, see the help topics about the job
type.
To find the job type of a job, use the Get-Job cmdlet. Get-Job returns
different job objects for different types of jobs. The value of the
PSJobTypeName property of the job objects that Get-Job returns indicates
the job type.
The following table lists the job types that come with PowerShell.
| Job Type | Description |
|---|---|
| BackgroundJob | Started using the Start-Job cmdlet. |
| RemoteJob | Started using the AsJob parameter of the |
Invoke-Command cmdlet. |
|
| PSWorkflowJob | Started using the AsJob parameter of a workflow. |
| PSScheduledJob | An instance of a scheduled job started by a job trigger. |
| CIMJob | Started using the AsJob parameter of a cmdlet from a |
| CDXML module. | |
| WMIJob | Started using the AsJob parameter of a cmdlet from a |
| WMI module. | |
| PSEventJob | Created usingRegister-ObjectEvent and specifying an |
| action with the Action parameter. |
NOTE: Before using the Get-Job cmdlet to get jobs of a particular type, verify
that the module that adds the job type is imported into the current session.
Otherwise, Get-Job does not get jobs of that type.
Examples
The following commands create a local background job, a remote background job,
a workflow job, and a scheduled job. Then, it uses the Get-Job cmdlet to get
the jobs. Get-Job does not get the scheduled job, but it gets any started
instances of the scheduled job.
Start a background job on the local computer.
PS> Start-Job -Name LocalData {Get-Process}
Id Name PSJobTypeName State HasMoreData Location Command
-- ---- ------------- ----- ----------- -------- -------
2 LocalData BackgroundJob Running True localhost Get-Process
Start a background job that runs on a remote computer.
PS> Invoke-Command -ComputerName Server01 {Get-Process} `
-AsJob -JobName RemoteData
Id Name PSJobTypeName State HasMoreData Location Command
-- ---- ------------- ----- ----------- -------- -------
2 RemoteData RemoteJob Running True Server01 Get-Process
Create a scheduled job
PS> Register-ScheduledJob -Name ScheduledJob -ScriptBlock `
{Get-Process} -Trigger (New-JobTrigger -Once -At "3 PM")
Id Name JobTriggers Command Enabled
-- ---- ----------- ------- -------
1 ScheduledJob 1 Get-Process True
Create a workflow.
PS> workflow Test-Workflow {Get-Process}
Run the workflow as a job.
PS> Test-Workflow -AsJob -JobName TestWFJob
Id Name PSJobTypeName State HasMoreData Location Command
-- ---- ------------- ----- ----------- -------- -------
2 TestWFJob PSWorkflowJob NotStarted True localhost Get-Process
Get the jobs. The Get-Job command does not get scheduled jobs, but it gets
instances of the scheduled job that are started.
PS> Get-Job
Id Name PSJobTypeName State HasMoreData Location Command
-- ---- ------------- ----- ----------- -------- -------
2 LocalData BackgroundJob Completed True localhost Get-Process
4 RemoteData RemoteJob Completed True Server01 Get-Process
6 TestWFJob PSWorkflowJob Completed True localhost WorkflowJob
8 ScheduledJob PSScheduledJob Completed True localhost Get-Process
To get scheduled jobs, use the Get-ScheduledJob cmdlet.
PS> Get-ScheduledJob
Id Name JobTriggers Command Enabled
-- ---- ----------- ------- -------
1 ScheduledJob 1 Get-Process True
