---
description: |
  The provisioner block defines how a provisioner is configured.
page_title: provisioner - build - Blocks
---

# The `provisioner` block

`@include 'from-1.5/beta-hcl2-note.mdx'`

The `provisioner` block defines how a provisioner is configured.

```hcl
# builds.pkr.hcl
build {
  # ...
  provisioner "shell" {
    inline = [
      "echo provisioning all the things",
      "echo the value of 'foo' is '${var.foo}'",
    ]
  }
}
```

Provisioners use builtin and third-party software to install and configure the
machine image after booting. Provisioners prepare the system for use.

The list of available provisioners can be found in the
[provisioners](/docs/provisioners) section.

## Run on Specific Sources

You can use the `only` or `except` configurations to run a provisioner only
with specific sources. These two configurations do what you expect: `only` will
only run the provisioner on the specified sources and `except` will run the
provisioner on anything other than the specified sources.

An example of `only` being used is shown below, but the usage of `except` is
effectively the same:

```hcl
# builds.pkr.hcl

source "amazon-ebs" "first-example" {
  #...
}

source "amazon-ebs" "second-example" {
  #...
}

build {
  sources = [
    "source.amazon-ebs.first-example",
    "source.amazon-ebs.second-example",
  ]
  provisioner "shell" {
    # This provisioner only runs for the 'first-example' source.
    only = ["amazon-ebs.first-example"]

    inline = [
      "echo provisioning all the things",
      "echo the value of 'foo' is '${var.foo}'",
    ]
  }
  provisioner "shell" {
    # This runs with all sources.
    inline = [
        "echo Hi World!"
      ]
  }
}
```

The source names within `only` and `except` must suppress `source.` prefix.

The values within `only` or `except` are _source names_, not builder types nor build names.

-> Note: In the cli `only` and `except` will match against **build names** (for
example:`my_build.amazon-ebs.first-example`) but in a provisioner they will
match on the **source name** (for example:`amazon-ebs.third-example`).

## Build-Specific Overrides

While the goal of Packer is to produce identical machine images, it sometimes
requires periods of time where the machines are different before they
eventually converge to be identical. In these cases, different configurations
for provisioners may be necessary depending on the build. This can be done
using build-specific overrides.

An example of where this might be necessary is when building both an EC2 AMI
and a VMware machine. The source EC2 AMI may setup a user with administrative
privileges by default, whereas the VMware machine doesn't have these
privileges. In this case, the shell script may need to be executed differently.
Of course, the goal is that hopefully the shell script converges these two
images to be identical. However, they may initially need to be run differently.

This example is shown below:

```hcl
source "null" "example1" {
  communicator = "none"
}

source "null" "example2" {
  communicator = "none"
}

source "null" "example3" {
  communicator = "none"
}

build {
  sources = ["source.null.example2", "source.null.example3"]

  source "source.null.example1" {
    // Give a name to this source
    name = "renamed"
  }

  provisioner "shell-local" {
    inline = ["echo not overridden"]
    override = {
      example3 = {
        inline = ["echo overrides for example3"]
      }
      // Refer to the source with the given name
      renamed = {
        inline = ["echo overrides for renamed"]
      }
    }
  }
}
```

As you can see, the `override` key is used. The value of this key is another
HCL attribute map where the key is the name of a [builder
definition](/docs/templates/hcl_templates/blocks/source). The value of this is in turn
another HCL attribute map. This HCL attribute map simply contains the provisioner
configuration as normal. This configuration is merged into the default
provisioner configuration.

## On Error Provisioner

You can optionally create a single specialized provisioner called an
`error-cleanup-provisioner`. This provisioner will not run unless the normal
provisioning run fails. If the normal provisioning run does fail, this special
error provisioner will run _before the instance is shut down_. This allows you
to make last minute changes and clean up behaviors that Packer may not be able
to clean up on its own.

For examples, users may use this provisioner to make sure that the instance is
properly unsubscribed from any services that it connected to during the build
run.

Toy usage example for the error cleanup script:

```hcl
source "null" "example" {
  communicator = "none"
}

build {
  sources = ["source.null.example"]

  provisioner "shell-local" {
    inline = ["exit 2"]
  }

  error-cleanup-provisioner "shell-local" {
    inline = ["echo 'rubber ducky'> ducky.txt"]
  }
}
```

## Pausing Before Running

With certain provisioners it is sometimes desirable to pause for some period of
time before running it. Specifically, in cases where a provisioner reboots the
machine, you may want to wait for some period of time before starting the next
provisioner.

Every provisioner definition in a Packer template can take a special
configuration `pause_before` that is the amount of time to pause before running
that provisioner. By default, there is no pause. An example is shown below:

```hcl
# builds.pkr.hcl
build {
  # ...
  provisioner "shell" {
      inline = [
        "echo provisioning all the things",
        "echo the value of 'foo' is '${var.foo}'",
      ]
      pause_before = "10s"
  }
}
```

For the above provisioner, Packer will wait 10 seconds before uploading and
executing the shell script.

## Retry on error

With certain provisioners it is sometimes desirable to retry when it fails.
Specifically, in cases where the provisioner depends on external processes that are not done yet.

Every provisioner definition in a Packer template can take a special
configuration `max_retries` that is the maximum number of times a provisioner will retry on error.
By default, there `max_retries` is zero and there is no retry on error. An example is shown below:

```hcl
# builds.pkr.hcl
build {
  # ...
  provisioner "shell" {
      inline = [
        "echo provisioning all the things",
        "echo the value of 'foo' is '${var.foo}'",
      ]
      max_retries = 5
  }
}
```

For the above provisioner, Packer will retry maximum five times until stops failing.
If after five retries the provisioner still fails, then the complete build will fail.

## Timeout

Sometimes a command can take much more time than expected

Every provisioner definition in a Packer template can take a special
configuration `timeout` that is the amount of time to wait before
considering that the provisioner failed. By default, there is no timeout. An
example is shown below:

```hcl
# builds.pkr.hcl
build {
  # ...
  provisioner "shell" {
      inline = [
        "echo provisioning all the things",
        "echo the value of 'foo' is '${var.foo}'",
      ]
      timeout = "5m"
  }
}
```

For the above provisioner, Packer will cancel the script if it takes more than
5 minutes.

Timeout has no effect in debug mode.

## Build Contextual Variables

Packer allows to access connection information and basic instance state information from a provisioner. These information are stored in the `build` variable.
Check out the [Contextual Variables](/docs/templates/hcl_templates/contextual-variables) documentation to learn more about and see some examples of how to use them.
