TOPIC
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 Windows PowerShell.
This topic is a supplement to the about_Jobs and about_Remote_Jobs topics.
Important: Background jobs that are started by using Start-Job or the AsJob
parameter of Invoke-Command rely on the Windows PowerShell
remoting infrastructure. To use these features, Windows
PowerShell must be configured for remoting, even if the
background job is runs only on the local computer.
For more information, see about_Remote_Requirements.
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 Windows PowerShell command prompt is
suppressed until the command is complete. But a background job does not
suppress the Windows 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 Windows PowerShell environment
(a "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
session (a 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 by 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 by 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 by
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 instance ID that differ
from the parent job so that you can manage the parent and child jobs
individually or as a unit.
To see the parent and child jobs in a job, use the Get-Job cmdlet to get
the parent job, and then pipe the job to a Format-List command that displays
the Name and ChildJobs properties of the objects, as shown in the following
command.
C:\PS> get-job | format-list -property Name, ChildJobs
Name : Job1
ChildJobs : {Job2}
You can also use a Get-Job command on the child job, as shown in the
following command:
C:\PS> get-job job2
Id Name State HasMoreData Location Command
-- ---- ----- ----------- -------- -------
2 Job2 Completed True localhost get-process
The configuration of the child job depends on the command that you use to
start the job.
-- When you use Start-Job to 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-Command to 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-Command to run a Start-Job command 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 by using the AsJob parameter of
Invoke-Command. (The backtick character [`] is the continuation character.)
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.
C:\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.
C:\PS> $j | format-list name, childjobs
Name : Job3
ChildJobs : {Job4, Job5, Job6}
When you display the parent job, it shows that the job failed.
C:\PS> $j
Id Name State HasMoreData Location Command
-- ---- ----- ----------- -------- -------
1 Job3 Failed True localhost,server... get-date
But when you run a Get-Job command on each of the child jobs, it shows
that only one failed.
PS C:\ps-test> get-job job4, job5, job6
Id Name State HasMoreData Location Command
-- ---- ----- ----------- -------- -------
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.
C:\PS> receive-job -job6 -keep | format-table ComputerName, DateTime -auto
ComputerName DateTime
------------ --------
Server02 Thursday, March 13, 2008 4:16:03 PM
The child jobs feature of Windows PowerShell background jobs gives you
more control over the jobs that you run.
SEE ALSO
about_Jobs
about_Remote_Jobs
about_Remote
Invoke-Command
Start-Job
Get-Job
Wait-Job
Stop-Job
Remove-Job
New-PSSession
Enter-PSSession
Exit-PSSession