DockerCLI/docs/reference/commandline/attach.md

attach

Usage: docker attach [OPTIONS] CONTAINER

Attach to a running container

  --no-stdin=false    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 daemonized process.

You can detach from the container and leave it running with CTRL-p CTRL-q (for a quiet exit) or with CTRL-c if --sig-proxy is false.

If --sig-proxy is true (the default),CTRL-c sends a SIGINT to the container.

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).

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