mirror of https://github.com/docker/cli.git
161 lines
6.1 KiB
Markdown
161 lines
6.1 KiB
Markdown
---
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title: "attach"
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description: "The attach command description and usage"
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keywords: "attach, running, container"
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---
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# attach
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```markdown
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Usage: docker attach [OPTIONS] CONTAINER
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Attach local standard input, output, and error streams to a running container
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Options:
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--detach-keys string Override the key sequence for detaching a container
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--help Print usage
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--no-stdin Do not attach STDIN
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--sig-proxy Proxy all received signals to the process (default true)
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```
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## Description
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Use `docker attach` to attach your terminal's standard input, output, and error
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(or any combination of the three) to a running container using the container's
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ID or name. This allows you to view its ongoing output or to control it
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interactively, as though the commands were running directly in your terminal.
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> **Note:**
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> The `attach` command will display the output of the `ENTRYPOINT/CMD` process. This
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> can appear as if the attach command is hung when in fact the process may simply
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> not be interacting with the terminal at that time.
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You can attach to the same contained process multiple times simultaneously,
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from different sessions on the Docker host.
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To stop a container, use `CTRL-c`. This key sequence sends `SIGKILL` to the
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container. If `--sig-proxy` is true (the default),`CTRL-c` sends a `SIGINT` to
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the container. You can detach from a container and leave it running using the
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`CTRL-p CTRL-q` key sequence.
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> **Note:**
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> A process running as PID 1 inside a container is treated specially by
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> Linux: it ignores any signal with the default action. So, the process
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> will not terminate on `SIGINT` or `SIGTERM` unless it is coded to do
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> so.
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It is forbidden to redirect the standard input of a `docker attach` command
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while attaching to a tty-enabled container (i.e.: launched with `-t`).
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While a client is connected to container's stdio using `docker attach`, Docker
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uses a ~1MB memory buffer to maximize the throughput of the application. If
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this buffer is filled, the speed of the API connection will start to have an
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effect on the process output writing speed. This is similar to other
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applications like SSH. Because of this, it is not recommended to run
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performance critical applications that generate a lot of output in the
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foreground over a slow client connection. Instead, users should use the
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`docker logs` command to get access to the logs.
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### Override the detach sequence
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If you want, you can configure an override the Docker key sequence for detach.
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This is useful if the Docker default sequence conflicts with key sequence you
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use for other applications. There are two ways to define your own detach key
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sequence, as a per-container override or as a configuration property on your
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entire configuration.
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To override the sequence for an individual container, use the
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`--detach-keys="<sequence>"` flag with the `docker attach` command. The format of
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the `<sequence>` is either a letter [a-Z], or the `ctrl-` combined with any of
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the following:
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* `a-z` (a single lowercase alpha character )
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* `@` (at sign)
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* `[` (left bracket)
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* `\\` (two backward slashes)
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* `_` (underscore)
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* `^` (caret)
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These `a`, `ctrl-a`, `X`, or `ctrl-\\` values are all examples of valid key
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sequences. To configure a different configuration default key sequence for all
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containers, see [**Configuration file** section](cli.md#configuration-files).
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## Examples
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### Attach to and detach from a running container
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```bash
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$ docker run -d --name topdemo ubuntu /usr/bin/top -b
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$ docker attach topdemo
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top - 02:05:52 up 3:05, 0 users, load average: 0.01, 0.02, 0.05
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Tasks: 1 total, 1 running, 0 sleeping, 0 stopped, 0 zombie
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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
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Mem: 373572k total, 355560k used, 18012k free, 27872k buffers
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Swap: 786428k total, 0k used, 786428k free, 221740k cached
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PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
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1 root 20 0 17200 1116 912 R 0 0.3 0:00.03 top
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top - 02:05:55 up 3:05, 0 users, load average: 0.01, 0.02, 0.05
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Tasks: 1 total, 1 running, 0 sleeping, 0 stopped, 0 zombie
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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
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Mem: 373572k total, 355244k used, 18328k free, 27872k buffers
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Swap: 786428k total, 0k used, 786428k free, 221776k cached
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PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
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1 root 20 0 17208 1144 932 R 0 0.3 0:00.03 top
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top - 02:05:58 up 3:06, 0 users, load average: 0.01, 0.02, 0.05
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Tasks: 1 total, 1 running, 0 sleeping, 0 stopped, 0 zombie
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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
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Mem: 373572k total, 355780k used, 17792k free, 27880k buffers
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Swap: 786428k total, 0k used, 786428k free, 221776k cached
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PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
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1 root 20 0 17208 1144 932 R 0 0.3 0:00.03 top
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^C$
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$ echo $?
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0
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$ docker ps -a | grep topdemo
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7998ac8581f9 ubuntu:14.04 "/usr/bin/top -b" 38 seconds ago Exited (0) 21 seconds ago topdemo
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```
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### Get the exit code of the container's command
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And in this second example, you can see the exit code returned by the `bash`
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process is returned by the `docker attach` command to its caller too:
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```bash
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$ docker run --name test -d -it debian
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275c44472aebd77c926d4527885bb09f2f6db21d878c75f0a1c212c03d3bcfab
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$ docker attach test
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root@f38c87f2a42d:/# exit 13
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exit
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$ echo $?
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13
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$ docker ps -a | grep test
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275c44472aeb debian:7 "/bin/bash" 26 seconds ago Exited (13) 17 seconds ago test
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```
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