packer-cn/website/pages/docs/provisioners/shell.mdx

---
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 - Provisioners
sidebar_title: 'Shell'
sidebar_current: docs-provisioners-shell-remote
---

# 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.

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

## Configuration Reference

@include 'provisioners/shell-config.mdx'

- `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.

- `env_var_format` (string) - When we parse the environment_vars that you
  provide, this gives us a string template to use in order to make sure that
  we are setting the environment vars correctly. By default it is `"%s='%s' "`.
  When used in conjunction with `use_env_var_file` the default is `"export %s='%s'\n"`

- `use_env_var_file` (boolean) - If true, Packer will write your environment
  variables to a tempfile and source them from that file, rather than
  declaring them inline in our execute_command. The default
  `execute_command` will be
  `chmod +x {{.Path}}; . {{.EnvVarFile}} && {{.Path}}`. This option is
  unnecessary for most cases, but if you have extra quoting in your custom
  `execute_command`, then this may be required for proper script
  execution. Default: false.

- `execute_command` (string) - The command to use to execute the script. By
  default this is `chmod +x {{ .Path }}; {{ .Vars }} {{ .Path }}`, unless the
  user has set `"use_env_var_file": true` -- in that case, the default
  `execute_command` is `chmod +x {{.Path}}; . {{.EnvVarFile}} && {{.Path}}`.
  This is a [template engine](/docs/templates/engine.html). Therefore, you may
  use user variables and template functions in this field. In addition, there
  are three available extra variables:

  - `Path` is the path to the script to run
  - `Vars` is the list of `environment_vars`, if configured.
  - `EnvVarFile` is the path to the file containing env vars, if
    `use_env_var_file` is true.

- `expect_disconnect` (boolean) - Defaults to `false`. When `true`, allow the server to disconnect from Packer without throwing an error.
  A disconnect might happen if you restart the ssh server or reboot the host.

- `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_folder` (string) - The folder where the uploaded script will reside
  on the machine. This defaults to '/tmp'.

- `remote_file` (string) - The filename the uploaded script will have on the
  machine. This defaults to 'script_nnn.sh'.

- `remote_path` (string) - The full path to the uploaded script will have on
  the machine. By default this is remote_folder/remote_file, if set this
  option will override both remote_folder and remote_file.

- `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.

- `pause_after` (string) - Wait the amount of time after provisioning a shell
  script, this pause be taken if all previous steps were successful.

@include 'provisioners/common-config.mdx'

## 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' | sudo -S sh -c '{{ .Vars }} {{ .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 above example won't work if your environment vars contain spaces or single
quotes; in these cases try removing the single quotes:

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

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 semantics. In
order for packer to pass environment variables you will need to change the
`execute_command` to:

```text
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](/docs/templates/builders.html#named-builds) 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.

- `PACKER_HTTP_ADDR` If using a builder that provides an http server for file
  transfer (such as hyperv, parallels, qemu, virtualbox, and vmware), this
  will be set to the address. You can use this address in your provisioner to
  download large files over http. This may be useful if you're experiencing
  slower speeds using the default file provisioner. A file provisioner using
  the `winrm` communicator may experience these types of difficulties.

## 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 use "pause_before" to make Packer wait before
executing the next script:

```json
{
  "type": "shell",
  "script": "script.sh",
  "pause_before": "10s",
  "timeout": "10s"
}
```

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:

```json
{
  "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 -e` 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.

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

## Quoting Environment Variables

Packer manages quoting for you, so you should't have to worry about it. Below
is an example of packer template inputs and what you should expect to get out:

```json
  "provisioners": [
    {
      "type":  "shell",
      "environment_vars": ["FOO=foo",
                           "BAR=bar's",
                           "BAZ=baz=baz",
                           "QUX==qux",
                           "FOOBAR=foo bar",
                           "FOOBARBAZ='foo bar baz'",
                           "QUX2=\"qux\""],
      "inline": ["echo \"FOO is $FOO\"",
                 "echo \"BAR is $BAR\"",
                 "echo \"BAZ is $BAZ\"",
                 "echo \"QUX is $QUX\"",
                 "echo \"FOOBAR is $FOOBAR\"",
                 "echo \"FOOBARBAZ is $FOOBARBAZ\"",
                 "echo \"QUX2 is $QUX2\""]
    }
```

Output:

```text
docker: FOO is foo
docker: BAR is bar's
docker: BAZ is baz=baz
docker: QUX is =qux
docker: FOOBAR is foo bar
docker: FOOBARBAZ is 'foo bar baz'
docker: QUX2 is "qux"
```