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---
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_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
<%= partial "partials/provisioners/shell-config" %>
- `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.
- `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 unnecessary 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}}`.
The value of this is treated as a [configuration
template](/docs/templates/engine.html). There are three available
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`. Whether to error if
the server disconnects us. 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.
<%= partial "partials/provisioners/common-config" %>
## 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:
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"
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