docker attachEstimated reading time: 5 minutes
Attach local standard input, output, and error streams to a running container
docker attach [OPTIONS] CONTAINER
||Override the key sequence for detaching a container|
||Do not attach STDIN|
||Proxy all received signals to the process|
|docker||The base command for the Docker CLI.|
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.
attachcommand will display the output of the
ENTRYPOINT/CMDprocess. 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
--sig-proxy is true (the default),
CTRL-c sends a
the container. If the container was run with
-t, 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
SIGTERMunless 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
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
<sequence> is either a letter [a-Z], or the
ctrl- combined with any of
a-z(a single lowercase alpha character )
\\(two backward slashes)
ctrl-\\ values are all examples of valid key
sequences. To configure a different configuration default key sequence for all
containers, see Configuration file section.
Attach to and detach from a running container
$ 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
process is returned by the
docker attach command to its caller too:
$ 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