为什么存在“-i”和“-t” “docker exec”的选项命令？ [英] Why do there exist "-i" and "-t" options for the "docker exec" command?

问题描述

老实说，我一直对 docker exec -it ... ， docker exec -i ... 感到困惑和 docker exec -t ... ，所以我决定做一个测试：

1. docker exec -it ... ：

    ＃docker exec  - 它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 
     

   该命令挂起，我必须使用 Ctl + c 中断




3. docker exec -t ... ：

    ＃docker exec -t 115c89122e72 bash 
    root @ 115c89122e72：/＃ls 
    ^ C 
     pre> 
    
    
   它成功进入容器，但挂起执行第一个c ommand。
    

所以，似乎没有必要让$ code> docker exec -i ... 和 docker exec -t ... 命令。任何人都可以详细说明为什么存在 docker exec -i 和 -t / code>命令？

解决方案

-i code> - 交互式保持STDIN打开，即使没有附加，如果你想输入任何命令，你需要的。

-t ， - tty 分配伪TTY，一个伪终端，将用户的终端连接到stdin和stdout。 （请参阅 容器/容器。 go ）

如果你做回音，只有 -t 需要。

但是对于输入输入的交互式会话，您需要 -i 。

由于 -i 保持stdin打开，它也用于将输入管道连接到已分离的Docker容器。即使使用 -d （detach）也可以使用。

请参阅什么时候在Docker容器中使用 - 交互式而不使用 - tty ：

  $ echo hello | docker run -i busybox cat 
 hello 
  

---

-i 保持STDIN打开即使不附加，在这种情况下STDOUT的状态是什么？

对于 docker exec ，由 docker运行。

但是，关于 docker exec ，目前有一个问题（问题8755：Docker tty不是tty与 docker exec




不幸的是，你的发现只相当于在centos6和ubuntu之间的tty的行为：14.04。在exec里面还没有一个功能的tty - 只要做$ code> ls -la / proc / self / fd / 0 ，看到它是一个破坏的链接，指向不存在的 pts 。

我们正在处理的实际错误是某些标准库假定/ proc / self / fds /中的符号链接必须是有效的符号链接

问题是，tty是在主机外部创建的，并且在容器中没有引用它，就像如何在...中设置 / dev / console 主容器。

解决这个问题的一个选项是分配并将主机中的 devpts 绑定到容器中。

To be honest, I have always been confused about docker exec -it …, docker exec -i … and docker exec -t …, so I decide to do a test:

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
   

   It works normally.

2. docker exec -i …:

   # docker exec -i 115c89122e72 bash
   ^C
   

   The command hangs and I have to use Ctl + c to interrupt it.

3. docker exec -t …:

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

   It enters the container successfully but hangs on executing the first command.

So it seems there is no point in having the docker exec -i … and docker exec -t … commands. Could anyone elaborate on why there exist -i and -t options for the docker exec command?

解决方案

-i, --interactive keeps STDIN open even if not attached, which you need if you want to type any command at all.

-t, --tty Allocates a pseudo-TTY, a pseudo terminal which connects a user's "terminal" with stdin and stdout. (See container/container.go)

If you do an echo, only -t is needed.
But for an interactive session where you enter inputs, you need -i.

Since -i keeps stdin open, it is also used in order to pipe input to a detached docker container. That would work even with -d (detach).
See "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?

It is, for docker exec, the one set by docker run.

But, regarding docker exec, there is a current issue (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.

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