Docker's --sig-proxy option sends all signals but one to a container. The exception s SIGCHLD, which is deliberately ignored as it doesn't make sense to send such a signal to a process in a container. Documentation updates will make this less confusing if anyone does attempt to do this. Docker-DCO-1.1-Signed-off-by: Matt Heon <mheon@redhat.com> (github: mheon)
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% DOCKER(1) Docker User Manuals % William Henry % APRIL 2014
NAME
docker-attach - Attach to a running container
SYNOPSIS
docker attach --no-stdin[=false] --sig-proxy[=true] CONTAINER
DESCRIPTION
If you docker run a container in detached mode (-d), you can reattach to the detached container with docker attach using the container's ID or name.
You can detach from the container again (and leave it running) with CTRL-q CTRL-q
(for a quiet exit), or CTRL-c
which will send a SIGKILL to the
container, or CTRL-\
to get a stacktrace of the Docker client when it quits.
When you detach from a container the exit code will be returned to
the client.
OPTIONS
--no-stdin=true|false When set to true, do not attach to stdin. The default is false.
--sig-proxy=true|false: When set to true, proxify received signals to the process (even in non-tty mode). SIGCHLD is not proxied. The default is true.
EXAMPLES
Attaching to a container
In this example the top command is run inside a container, from an image called fedora, in detached mode. The ID from the container is passed into the docker attach command:
# ID=$(sudo docker run -d fedora /usr/bin/top -b)
# sudo docker attach $ID
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
HISTORY
April 2014, Originally compiled by William Henry (whenry at redhat dot com) based on docker.io source material and internal work.