--- title: "attach" description: "The attach command description and usage" keywords: "attach, running, container" --- # attach ```markdown Usage: docker attach [OPTIONS] CONTAINER Attach local standard input, output, and error streams to a running container Options: --detach-keys string Override the key sequence for detaching a container --help Print usage --no-stdin Do not attach STDIN --sig-proxy Proxy all received signals to the process (default true) ``` ## Description Use `docker attach` to attach your terminal's standard input, output, and error (or any combination of the three) to a running container using the container's ID or name. This allows you to view its ongoing output or to control it interactively, as though the commands were running directly in your terminal. > **Note:** > The `attach` command will display the output of the `ENTRYPOINT/CMD` process. This > can appear as if the attach command is hung when in fact the process may simply > not be interacting with the terminal at that time. You can attach to the same contained process multiple times simultaneously, from different sessions on the Docker host. 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=""` flag with the `docker attach` command. The format of the `` 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 ### Attach to and detach from a running container ```bash $ 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 ``` ### Get the exit code of the container's command 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: ```bash $ docker run --name test -d -it debian 275c44472aebd77c926d4527885bb09f2f6db21d878c75f0a1c212c03d3bcfab $ docker attach test root@f38c87f2a42d:/# exit 13 exit $ echo $? 13 $ docker ps -a | grep test 275c44472aeb debian:7 "/bin/bash" 26 seconds ago Exited (13) 17 seconds ago test ```