---
description: |
    The shell Packer provisioner provisions machines built by Packer using shell
    scripts. Shell provisioning is the easiest way to get software installed and
    configured on a machine.
layout: docs
page_title: Shell Provisioner
...

# Shell Provisioner

Type: `shell`

The shell Packer provisioner provisions machines built by Packer using shell
scripts. Shell provisioning is the easiest way to get software installed and
configured on a machine.

-> **Building Windows images?** You probably want to use the
[PowerShell](/docs/provisioners/powershell.html) or [Windows
Shell](/docs/provisioners/windows-shell.html) provisioners.

## Basic Example

The example below is fully functional.

``` {.javascript}
{
  "type": "shell",
  "inline": ["echo foo"]
}
```

## Configuration Reference

The reference of available configuration options is listed below. The only
required element is either "inline" or "script". Every other option is optional.

Exactly *one* of the following is required:

-   `inline` (array of strings) - This is an array of commands to execute. The
    commands are concatenated by newlines and turned into a single file, so they
    are all executed within the same context. This allows you to change
    directories in one command and use something in the directory in the next
    and so on. Inline scripts are the easiest way to pull off simple tasks
    within the machine.

-   `script` (string) - The path to a script to upload and execute in
    the machine. This path can be absolute or relative. If it is relative, it is
    relative to the working directory when Packer is executed.

-   `scripts` (array of strings) - An array of scripts to execute. The scripts
    will be uploaded and executed in the order specified. Each script is
    executed in isolation, so state such as variables from one script won't
    carry on to the next.

Optional parameters:

-   `binary` (boolean) - If true, specifies that the script(s) are binary files,
    and Packer should therefore not convert Windows line endings to Unix line
    endings (if there are any). By default this is false.

-   `environment_vars` (array of strings) - An array of key/value pairs to
    inject prior to the execute\_command. The format should be `key=value`.
    Packer injects some environmental variables by default into the environment,
    as well, which are covered in the section below.

-   `execute_command` (string) - The command to use to execute the script. By
    default this is `chmod +x {{ .Path }}; {{ .Vars }} {{ .Path }}`. The value
    of this is treated as [configuration
    template](/docs/templates/configuration-templates.html). There are two
    available variables: `Path`, which is the path to the script to run, and
    `Vars`, which is the list of `environment_vars`, if configured.

-   `inline_shebang` (string) - The
    [shebang](https://en.wikipedia.org/wiki/Shebang_%28Unix%29) value to use when
    running commands specified by `inline`. By default, this is `/bin/sh -e`. If
    you're not using `inline`, then this configuration has no effect.
    **Important:** If you customize this, be sure to include something like the
    `-e` flag, otherwise individual steps failing won't fail the provisioner.

-   `remote_path` (string) - The filename where the script will be uploaded
    to in the machine. This defaults to `/tmp/script_nnn.sh` where "nnn" is
    a randomly generated number. This value must be a writable location and
    any parent directories must already exist.

-   `skip_clean` (boolean) - If true, specifies that the helper scripts 
    uploaded to the system will not be removed by Packer. This defaults to 
    false (clean scripts from the system).

-   `start_retry_timeout` (string) - The amount of time to attempt to *start*
    the remote process. By default this is `5m` or 5 minutes. This setting
    exists in order to deal with times when SSH may restart, such as a
    system reboot. Set this to a higher value if reboots take a longer amount
    of time.

## Execute Command Example

To many new users, the `execute_command` is puzzling. However, it provides an
important function: customization of how the command is executed. The most
common use case for this is dealing with **sudo password prompts**. You may also
need to customize this if you use a non-POSIX shell, such as `tcsh` on FreeBSD.

### Sudo Example

Some operating systems default to a non-root user. For example if you login as
`ubuntu` and can sudo using the password `packer`, then you'll want to change
`execute_command` to be:

``` {.text}
"echo 'packer' | {{ .Vars }} sudo -E -S sh '{{ .Path }}'"
```

The `-S` flag tells `sudo` to read the password from stdin, which in this case
is being piped in with the value of `packer`. The `-E` flag tells `sudo` to
preserve the environment, allowing our environmental variables to work within
the script.

By setting the `execute_command` to this, your script(s) can run with root
privileges without worrying about password prompts.

### FreeBSD Example

FreeBSD's default shell is `tcsh`, which deviates from POSIX sematics. In order
for packer to pass environment variables you will need to change the
`execute_command` to:

    chmod +x {{ .Path }}; env {{ .Vars }} {{ .Path }}

Note the addition of `env` before `{{ .Vars }}`.

## Default Environmental Variables

In addition to being able to specify custom environmental variables using the
`environment_vars` configuration, the provisioner automatically defines certain
commonly useful environmental variables:

-   `PACKER_BUILD_NAME` is set to the name of the build that Packer is running.
    This is most useful when Packer is making multiple builds and you want to
    distinguish them slightly from a common provisioning script.

-   `PACKER_BUILDER_TYPE` is the type of the builder that was used to create the
    machine that the script is running on. This is useful if you want to run
    only certain parts of the script on systems built with certain builders.

## Handling Reboots

Provisioning sometimes involves restarts, usually when updating the operating
system. Packer is able to tolerate restarts via the shell provisioner.

Packer handles this by retrying to start scripts for a period of time before
failing. This allows time for the machine to start up and be ready to run
scripts. The amount of time the provisioner will wait is configured using
`start_retry_timeout`, which defaults to a few minutes.

Sometimes, when executing a command like `reboot`, the shell script will return
and Packer will start executing the next one before SSH actually quits and the
machine restarts. For this, put a long `sleep` after the reboot so that SSH will
eventually be killed automatically:

``` {.text}
reboot
sleep 60
```

Some OS configurations don't properly kill all network connections on reboot,
causing the provisioner to hang despite a reboot occurring. In this case, make
sure you shut down the network interfaces on reboot or in your shell script. For
example, on Gentoo:

``` {.text}
/etc/init.d/net.eth0 stop
```

## SSH Agent Forwarding

Some provisioning requires connecting to remote SSH servers from within the
packer instance. The below example is for pulling code from a private git
repository utilizing openssh on the client. Make sure you are running
`ssh-agent` and add your git repo ssh keys into it using `ssh-add /path/to/key`.
When the packer instance needs access to the ssh keys the agent will forward the
request back to your `ssh-agent`.

Note: when provisioning via git you should add the git server keys into the
`~/.ssh/known_hosts` file otherwise the git command could hang awaiting input.
This can be done by copying the file in via the [file
provisioner](/docs/provisioners/file.html) (more secure) or using `ssh-keyscan`
to populate the file (less secure). An example of the latter accessing github
would be:

{ "type": "shell", "inline": \[ "sudo apt-get install -y git", "ssh-keyscan
github.com >> \~/.ssh/known\_hosts", "git clone
git@github.com:exampleorg/myprivaterepo.git" \] }

## Troubleshooting

*My shell script doesn't work correctly on Ubuntu*

-   On Ubuntu, the `/bin/sh` shell is
    [dash](https://en.wikipedia.org/wiki/Debian_Almquist_shell). If your script
    has [bash](https://en.wikipedia.org/wiki/Bash_(Unix_shell))-specific commands
    in it, then put `#!/bin/bash` at the top of your script. Differences between
    dash and bash can be found on the
    [DashAsBinSh](https://wiki.ubuntu.com/DashAsBinSh) Ubuntu wiki page.

*My shell works when I login but fails with the shell provisioner*

-   See the above tip. More than likely, your login shell is using `/bin/bash`
    while the provisioner is using `/bin/sh`.

*My installs hang when using `apt-get` or `yum`*

-   Make sure you add a `-y` to the command to prevent it from requiring user
    input before proceeding.

*How do I tell what my shell script is doing?*

-   Adding a `-x` flag to the shebang at the top of the script (`#!/bin/sh -x`)
    will echo the script statements as it is executing.

*My builds don't always work the same*

-   Some distributions start the SSH daemon before other core services which can
    create race conditions. Your first provisioner can tell the machine to wait
    until it completely boots.

``` {.javascript}
{
  "type": "shell",
  "inline": [ "sleep 10" ]
}
```