linux - "-i"命令的 "-t"和 "docker exec"选项的用途是什么？

Question

说实话，我一直对docker exec -it ...、docker exec -i ...和docker exec -t ...感到困惑>，所以我决定做一个测试:

1. docker exec -it ...:

   # docker exec -it 115c89122e72 bash
   root@115c89122e72:/# ls
   bin  boot  dev  etc  home  lib  lib64  media  mnt  opt  proc  root  run  sbin  srv  sys  tmp  usr  var
   

   正常工作。

2. docker exec -i ...:

   # docker exec -i 115c89122e72 bash
   ^C
   

   命令挂起，我必须使用 Ctl + c 来中断它。

3. docker exec -t ...:

   # docker exec -t 115c89122e72 bash
   root@115c89122e72:/# ls
   ^C
   

   成功进入容器，但执行第一个命令时挂起。

因此，使用 docker exec -i ... 和 docker exec -t ... 命令似乎没有意义。谁能详细说明为什么 docker exec 命令存在 -i 和 -t 选项？

Answer 1

-i, --interactive 即使没有附加 STDIN 也会保持打开状态，如果你想键入任何命令，你需要它。

-t, --tty 分配一个伪TTY，一个pseudo terminal它将用户的“终端”与标准输入和标准输出连接起来。 (见 container/container.go)

如果做回显，只需要-t。
但是对于输入输入的交互式 session ，您需要 -i.

由于 -i 保持标准输入处于打开状态，它也用于将输入通过管道传输到分离的 docker 容器。即使使用 -d (分离)也可以。
见“When would I use --interactive without --tty in a Docker container?”:

$ echo hello | docker run -i busybox cat
  hello

---

-i keeps STDIN open even if not attached, what is the status of STDOUT in this case?

docker exec 是 docker run 设置的。

但是，关于 docker exec ，当前存在一个问题 (issue 8755: Docker tty is not a tty with docker exec

unfortunately your discovery only amounts to a difference between the behaviour of tty in centos6 vs ubuntu:14.04. There is still not a functional tty inside the exec - just do ls -la /proc/self/fd/0 and see that it's a broken link pointing to a pts which doesn't exist.

the actual bug we're dealing with is that certain standard libraries assume that the symlinks in /proc/self/fds/ must be valid symlinks

The problem is that the tty is created outside on the host and there is no reference to it in the container like how /dev/console is setup in the primary container.
One options to fix this would be allocate and bind mount the devpts from the host in to the containers.

注(2017 年第四季度):this should been fixed by now (docker 17.06-ce) .
见 PR 33007 .

该 PR 现在允许(自 17.06 起):

zacharys-pro:dev razic$ docker run --rm -t -d ubuntu bash
83c292c8e2d13d1b1a8b34680f3fb95c2b2b3fef71d4ce2b6e12c954ae50965a

zacharys-pro:dev razic$ docker ps
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS               NAMES
83c292c8e2d1        ubuntu              "bash"              2 seconds ago       Up 1 second                             xenodochial_bardeen

zacharys-pro:dev razic$ docker exec -ti xenodochial_bardeen tty
/dev/pts/1

(在 17.06 之前，tty 返回“not a tty”)