DockerCLI/docs/reference/commandline/attach.md

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title = "attach"
description = "The attach command description and usage"
keywords = ["attach, running, container"]
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# attach

    Usage: docker attach [OPTIONS] CONTAINER

    Attach to a running container

      --detach-keys="<sequence>"       Set up escape key sequence
      --help                           Print usage
      --no-stdin                       Do not attach STDIN
      --sig-proxy=true                 Proxy all received signals to the process

The `docker attach` command allows you to attach to a running container using
the container's ID or name, either to view its ongoing output or to control it
interactively. You can attach to the same contained process multiple times
simultaneously, screen sharing style, or quickly view the progress of your
detached  process.

To stop a container, use `CTRL-c`. This key sequence sends `SIGKILL` to the
container. If `--sig-proxy` is true (the default),`CTRL-c` sends a `SIGINT` to
the container. You can detach from a container and leave it running using the
 `CTRL-p CTRL-q` key sequence.

> **Note:**
> A process running as PID 1 inside a container is treated specially by
> Linux: it ignores any signal with the default action. So, the process
> will not terminate on `SIGINT` or `SIGTERM` unless it is coded to do
> so.

It is forbidden to redirect the standard input of a `docker attach` command
while attaching to a tty-enabled container (i.e.: launched with `-t`).

While a client is connected to container's stdio using `docker attach`, Docker 
uses a ~1MB memory buffer to maximize the throughput of the application. If 
this buffer is filled, the speed of the API connection will start to have an 
effect on the process output writing speed. This is similar to other 
applications like SSH. Because of this, it is not recommended to run 
performance critical applications that generate a lot of output in the 
foreground over a slow client connection. Instead, users should use the 
`docker logs` command to get access to the logs.


## Override the detach sequence

If you want, you can configure an override the Docker key sequence for detach.
This is useful if the Docker default sequence conflicts with key sequence you
use for other applications. There are two ways to define your own detach key
sequence, as a per-container override or as a configuration property on  your
entire configuration.

To override the sequence for an individual container, use the
`--detach-keys="<sequence>"` flag with the `docker attach` command. The format of
the `<sequence>` is either a letter [a-Z], or the `ctrl-` combined with any of
the following:

* `a-z` (a single lowercase alpha character )
* `@` (at sign)
* `[` (left bracket)
* `\\` (two backward slashes)
*  `_` (underscore)
* `^` (caret)

These `a`, `ctrl-a`, `X`, or `ctrl-\\` values are all examples of valid key
sequences. To configure a different configuration default key sequence for all
containers, see [**Configuration file** section](cli.md#configuration-files).

#### Examples

    $ docker run -d --name topdemo ubuntu /usr/bin/top -b
    $ docker attach topdemo
    top - 02:05:52 up  3:05,  0 users,  load average: 0.01, 0.02, 0.05
    Tasks:   1 total,   1 running,   0 sleeping,   0 stopped,   0 zombie
    Cpu(s):  0.1%us,  0.2%sy,  0.0%ni, 99.7%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
    Mem:    373572k total,   355560k used,    18012k free,    27872k buffers
    Swap:   786428k total,        0k used,   786428k free,   221740k cached

    PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
     1 root      20   0 17200 1116  912 R    0  0.3   0:00.03 top

     top - 02:05:55 up  3:05,  0 users,  load average: 0.01, 0.02, 0.05
     Tasks:   1 total,   1 running,   0 sleeping,   0 stopped,   0 zombie
     Cpu(s):  0.0%us,  0.2%sy,  0.0%ni, 99.8%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
     Mem:    373572k total,   355244k used,    18328k free,    27872k buffers
     Swap:   786428k total,        0k used,   786428k free,   221776k cached

       PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
           1 root      20   0 17208 1144  932 R    0  0.3   0:00.03 top


     top - 02:05:58 up  3:06,  0 users,  load average: 0.01, 0.02, 0.05
     Tasks:   1 total,   1 running,   0 sleeping,   0 stopped,   0 zombie
     Cpu(s):  0.2%us,  0.3%sy,  0.0%ni, 99.5%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
     Mem:    373572k total,   355780k used,    17792k free,    27880k buffers
     Swap:   786428k total,        0k used,   786428k free,   221776k cached

     PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
          1 root      20   0 17208 1144  932 R    0  0.3   0:00.03 top
    ^C$
    $ echo $?
    0
    $ docker ps -a | grep topdemo
    7998ac8581f9        ubuntu:14.04        "/usr/bin/top -b"   38 seconds ago      Exited (0) 21 seconds ago                          topdemo

And in this second example, you can see the exit code returned by the `bash`
process is returned by the `docker attach` command to its caller too:

    $ docker run --name test -d -it debian
    275c44472aebd77c926d4527885bb09f2f6db21d878c75f0a1c212c03d3bcfab
    $ docker attach test
    $$ exit 13
    exit
    $ echo $?
    13
    $ docker ps -a | grep test
    275c44472aeb        debian:7            "/bin/bash"         26 seconds ago      Exited (13) 17 seconds ago                         test