docker下ubuntu18.04的binfmt_misc问题

Question

尝试在docker容器中运行ubuntu:18.04下的cross chroot。

在尝试安装binfmt-support (qemu-user-static的依赖项)时，会发生以下情况：

~ docker run -it ubuntu:18.04 /bin/bash
root@df5a34a47fe2:/# cd
root@df5a34a47fe2:~# apt-get update
...
root@df5a34a47fe2:~# apt-get install qemu-user-static
...
Setting up qemu-user-static (1:2.11+dfsg-1ubuntu7.9) ...
mount: /proc/sys/fs/binfmt_misc: permission denied.
update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
mount: /proc/sys/fs/binfmt_misc: permission denied.
update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
mount: /proc/sys/fs/binfmt_misc: permission denied.
update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
mount: /proc/sys/fs/binfmt_misc: permission denied.
update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
mount: /proc/sys/fs/binfmt_misc: permission denied.
update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
mount: /proc/sys/fs/binfmt_misc: permission denied.
update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
mount: /proc/sys/fs/binfmt_misc: permission denied.
update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
mount: /proc/sys/fs/binfmt_misc: permission denied.
update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
mount: /proc/sys/fs/binfmt_misc: permission denied.
update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
mount: /proc/sys/fs/binfmt_misc: permission denied.
update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
mount: /proc/sys/fs/binfmt_misc: permission denied.
update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
mount: /proc/sys/fs/binfmt_misc: permission denied.
update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
mount: /proc/sys/fs/binfmt_misc: permission denied.
update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
mount: /proc/sys/fs/binfmt_misc: permission denied.
update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
mount: /proc/sys/fs/binfmt_misc: permission denied.
update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
mount: /proc/sys/fs/binfmt_misc: permission denied.
update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
mount: /proc/sys/fs/binfmt_misc: permission denied.
update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
mount: /proc/sys/fs/binfmt_misc: permission denied.
update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
mount: /proc/sys/fs/binfmt_misc: permission denied.
update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
mount: /proc/sys/fs/binfmt_misc: permission denied.
update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
mount: /proc/sys/fs/binfmt_misc: permission denied.
update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
Setting up binfmt-support (2.1.8-2) ...
invoke-rc.d: could not determine current runlevel
invoke-rc.d: policy-rc.d denied execution of start.
root@df5a34a47fe2:~# echo $?
0

有没有人知道这里发生了什么，是否相关以及如何修复？

Answer 1

binfmt正在尝试将qemu注册为二进制加载器，这样您就不需要在每次需要使用qemu运行二进制文件时都调用它。要做到这一点，需要容器没有的特权。

忽略这些警告，因为在构建映像时在主机上注册binfmt是没有意义的。