github.com/Ilhicas/nomad@v1.0.4-0.20210304152020-e86851182bc3/website/content/docs/commands/alloc/exec.mdx (about)

     1  ---
     2  layout: docs
     3  page_title: 'Commands: alloc exec'
     4  sidebar_title: exec
     5  description: |
     6    Runs a command in a container.
     7  ---
     8  
     9  # Command: alloc exec
    10  
    11  **Alias: `nomad exec`**
    12  
    13  The `alloc exec` command runs a command in a running allocation.
    14  
    15  ## Usage
    16  
    17  ```plaintext
    18  nomad alloc exec [options] <allocation> <command> [<args>...]
    19  ```
    20  
    21  The nomad exec command can be use to run commands inside a running task/allocation.
    22  
    23  Use cases are for inspecting container state, debugging a failed application
    24  without needing ssh access into the node that's running the allocation.
    25  
    26  This command executes the command in the given task in the allocation. If the
    27  allocation is only running a single task, the task name can be omitted.
    28  Optionally, the `-job` option may be used in which case a random allocation from
    29  the given job will be chosen.
    30  
    31  When ACLs are enabled, this command requires a token with the `alloc-exec`,
    32  `read-job`, and `list-jobs` capabilities for the allocation's namespace. If
    33  the task driver does not have file system isolation (as with `raw_exec`),
    34  this command requires the `alloc-node-exec`, `read-job`, and `list-jobs`
    35  capabilities for the allocation's namespace.
    36  
    37  ## General Options
    38  
    39  @include 'general_options.mdx'
    40  
    41  ## Exec Options
    42  
    43  - `-task`: Sets the task to exec command in.
    44  
    45  - `-job`: Use a random allocation from the specified job ID.
    46  
    47  - `-i`: Pass stdin to the container, defaults to true. Pass `-i=false` to
    48    disable explicitly.
    49  
    50  - `-t`: Allocate a pseudo-tty, defaults to true if stdin is detected to be a tty
    51    session. Pass `-t=false` to disable explicitly.
    52  
    53  - `-e` <escape_char>: Sets the escape character for sessions with a pty
    54    (default: '~'). The escape character is only recognized at the beginning of a
    55    line. The escape character followed by a dot ('.') closes the connection.
    56    Setting the character to 'none' disables any escapes and makes the session
    57    fully transparent.
    58  
    59  ## Examples
    60  
    61  To start an interactive debugging session in a particular alloc, invoke exec
    62  command with your desired shell available inside the task:
    63  
    64  ```shell-session
    65  $ nomad alloc exec eb17e557 /bin/bash
    66  root@eb17e557:/data# # now run any debugging commands inside container
    67  root@eb17e557:/data# # ps -ef
    68  ```
    69  
    70  To run a command and stream results without starting an interactive shell, you
    71  can pass the command and its arguments to exec directly:
    72  
    73  ```shell-session# run commands without starting an interactive session
    74  $ nomad alloc exec eb17e557 cat /etc/resolv.conf
    75  ...
    76  ```
    77  
    78  When passing command arguments to be evaluated in task, you may need to ensure
    79  that your host shell doesn't interpolate values before invoking `exec` command.
    80  For example, the following command would return the environment variable on
    81  operator shell rather than task containers:
    82  
    83  ```shell-session
    84  $ nomad alloc exec eb17e557 echo $NOMAD_ALLOC_ID # wrong
    85  ...
    86  ```
    87  
    88  Here, we must start a shell in task to interpolate `$NOMAD_ALLOC_ID`, and quote
    89  command or use the [heredoc syntax][heredoc]
    90  
    91  ```shell-session# by quoting argument
    92  $ nomad alloc exec eb17e557 /bin/sh -c 'echo $NOMAD_ALLOC_ID'
    93  eb17e557-443e-4c51-c049-5bba7a9850bc
    94  
    95  $ # by using heredoc and passing command in stdin
    96  $ nomad alloc exec eb17e557 /bin/sh <<'EOF'
    97  > echo $NOMAD_ALLOC_ID
    98  > EOF
    99  eb17e557-443e-4c51-c049-5bba7a9850bc
   100  ```
   101  
   102  This technique applies when aiming to run a shell pipeline without streaming
   103  intermediate command output across the network:
   104  
   105  ```shell-session# e.g. find top appearing lines in some output
   106  $ nomad alloc exec eb17e557 /bin/sh -c 'cat /output | sort | uniq -c | sort -rn | head -n 5'
   107  ...
   108  ```
   109  
   110  ## Using Job ID instead of Allocation ID
   111  
   112  Setting the `-job` flag causes a random allocation of the specified job to be
   113  selected.
   114  
   115  ```plaintext
   116  nomad alloc exec -job <job-id> <command> [<args>...]
   117  ```
   118  
   119  Choosing a specific allocation is useful for debugging issues with a specific
   120  instance of a service. For other operations using the `-job` flag may be more
   121  convenient than looking up an allocation ID to use.
   122  
   123  ## Disabling remote execution
   124  
   125  `alloc exec` is enabled by default to aid with debugging. Operators can disable
   126  the feature by setting [`disable_remote_exec` client config
   127  option][disable_remote_exec_flag] on all clients, or a subset of clients that
   128  run sensitive workloads.
   129  
   130  ## Exec targeting a specific task
   131  
   132  When trying to `alloc exec` for a job that has more than one task associated
   133  with it, you may want to target a specific task.
   134  
   135  ```shell-session
   136  # open a shell session in one of your allocation's tasks
   137  $ nomad alloc exec -i -t -task mytask a1827f93 /bin/bash
   138  a1827f93$
   139  ```
   140  
   141  [heredoc]: http://tldp.org/LDP/abs/html/here-docs.html
   142  [disable_remote_exec_flag]: /docs/configuration/client#disable_remote_exec