--- 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 --- # 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) or [Windows Shell](/docs/provisioners/windows-shell) provisioners. ## Basic Example The example below is fully functional. ```json { "type": "shell", "inline": ["echo foo"] } ``` ```hcl provisioner "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). 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#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" } ``` ```hcl provisioner "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) (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" ] } ``` ```hcl provisioner "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]()-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"] } ``` ```hcl provisioner "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\""] } ] ``` ```hcl provisioner "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" ```