open-nomad/website/source/docs/commands/alloc/exec.html.md.erb

---
layout: "docs"
page_title: "Commands: alloc exec"
sidebar_current: "docs-commands-alloc-exec"
description: >
  Runs a command in a container.
---

# Command: alloc exec <sup>0.9.2</sup>
**Alias: `nomad exec`**

The `alloc exec` command runs a command in a running allocation.

## Usage

```
nomad alloc exec [options] <allocation> <command> [<args>...]
```


The nomad exec command can be use to run commands inside a running task/allocation.

Use cases are for inspecting container state, debugging a failed application
without needing ssh access into the node that's running the allocation.

This command executes the command in the given task in the allocation.  If the
allocation is only running a single task, the task name can be omitted.
Optionally, the `-job` option may be used in which case a random allocation from
the given job will be chosen.

## General Options

<%= partial "docs/commands/_general_options" %>

## Exec Options

* `task`: Sets the task to exec command in.  Defaults to first task.

* `-job`: Use a random allocation from the specified job ID.

* `-i`: Pass stdin to the container, defaults to true.
Pass `-i=false` to disable explicitly.

* `-t`: Allocate a pseudo-tty, defaults to true if stdin is detected to be a tty session.
Pass `-t=false` to disable explicitly.

* `-e` <escape_char>: Sets the escape character for sessions with a pty
(default: '~'). The escape character is only recognized at the beginning of a
line. The escape character followed by a dot ('.') closes the connection.
Setting the character to 'none' disables any escapes and makes the session fully
transparent.


## Examples

To start an interactive debugging session in a particular alloc, invoke exec
command with your desired shell available inside the task:

```
$ nomad alloc exec eb17e557 /bin/bash
root@eb17e557:/data# # now run any debugging commands inside container
root@eb17e557:/data# # ps -ef
```

To run a command and stream results without starting an interactive shell, you
can pass the command and its arguments to exec directly:

```
$ # run commands without starting an interactive session
$ nomad alloc exec eb17e557 cat /etc/resolv.conf
```

When passing command arguments to be evaluated in task, you may need to ensure
that your host shell doesn't interpolate values before invoking `exec` command.
For example, the following command would return the environment variable on
operator shell rather than task containers:

```
$ nomad alloc exec eb17e557 echo $NOMAD_ALLOC_ID # wrong
```

Here, we must start a shell in task to interpolate `$NOMAD_ALLOC_ID`, and quote
command or use the [heredoc syntax][heredoc]

```
$ # by quoting argument
$ nomad alloc exec eb17e557 /bin/sh -c 'echo $NOMAD_ALLOC_ID'
eb17e557-443e-4c51-c049-5bba7a9850bc

$ # by using heredoc and passing command in stdin
$ nomad alloc exec eb17e557 /bin/sh <<'EOF'
> echo $NOMAD_ALLOC_ID
> EOF
eb17e557-443e-4c51-c049-5bba7a9850bc
```

This technique applies when aiming to run a shell pipeline without streaming
intermediate command output across the network:

```
$ # e.g. find top appearing lines in some output
$ nomad alloc exec eb17e557 /bin/sh -c 'cat /output | sort | uniq -c | sort -rn | head -n 5'
```

[heredoc]: http://tldp.org/LDP/abs/html/here-docs.html

## Using Job ID instead of Allocation ID

Setting the `-job` flag causes a random allocation of the specified job to be
selected.

```
nomad alloc exec -job <job-id> <command> [<args>...]
```


Choosing a specific allocation is useful for debugging issues with a specific
instance of a service. For other operations using the `-job` flag may be more
convenient than looking up an allocation ID to use.