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
orSIGTERM
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 defines a 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.
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
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