![ptys 无法在 lxc 下的 chroot 中工作](https://linux22.com/image/117553/ptys%20%E6%97%A0%E6%B3%95%E5%9C%A8%20lxc%20%E4%B8%8B%E7%9A%84%20chroot%20%E4%B8%AD%E5%B7%A5%E4%BD%9C.png)
我正在尝试在 lxc 下使用 chroots 进行开发。我在 lxc 容器配置中启用了“嵌套”选项,并将安装的 proc 和 devpts 绑定到我的 chroot 中,就像 chroot 位于普通 Linux 机器上一样。
不幸的是,当我尝试在 chroot 中使用需要 ptys 的东西(例如“script”命令)时,我收到如下错误
root@manualdev:~# chroot /chroots/jessie-staging/
root@manualdev:/# script
script: openpty failed: No such file or directory
Terminated
root@manualdev:/#
系统信息:
- 主机内核是 4.4.0-79-generic
- 主机发行版是 Ubuntu xenial
- 主机架构为arm64
- 容器发行版是 Debian Stretch
- 容器和chroot架构是armhf
- Chroot 发行版是 Raspbian(使用 jessie、stretch 和 buster 进行测试)
答案1
解决这个问题的方法(通过有根据的猜测发现)是在 chroot 中执行以下命令。
rm /dev/ptmx
ln -s /dev/pts/ptmx /dev/ptmx
我不是 100% 确定,但我相信需要这样做的原因是 lxc 对 /dev/pts 使用“多实例模式”。根据文档https://github.com/torvalds/linux/blob/v4.4/Documentation/filesystems/devpts.txt
如果 CONFIG_DEVPTS_MULTIPLE_INSTANCES=y 并指定了 'newinstance' 选项,则挂载被视为处于多实例模式,并创建 devpts fs 的新实例。在此实例中创建的任何 pty 都独立于其他 devpt 实例中的 pty。与单实例模式一样,/dev/pts/ptmx 节点也存在。要有效使用多实例模式,必须使用符号链接或绑定安装将 /dev/ptmx 的打开重定向到“/dev/pts/ptmx”。
查看该文件的更新版本,似乎更新的内核可能不需要这样做。
答案2
需要安装管理伪终端的 devpts 文件系统:
魔法命令是:
(以 root 身份)# mount -t devpts devpts /dev/pts
这是一个检查伪终端系统是否正常工作的会话:
root@e7440:/me/media/20230104a# mount |grep pts # Check, yup no devpts mounted
root@e7440:/me/media/20230104a# ls -lai /dev/pt* # /dev/ptmx exists, but /dev/pts is empty
233300 crw-rw-rw- 1 root root 5, 2 Jan 4 23:07 /dev/ptmx
/dev/pts:
total 8
237675 drwxr-xr-x 2 root root 4096 Jan 4 23:04 .
229757 drwxr-xr-x 4 root root 4096 Jan 3 14:31 ..
root@e7440:/me/media/20230104a# mount -t devpts devpts /dev/pts
root@e7440:/me/media/20230104a# mount |grep pts
devpts on /dev/pts type devpts (rw)
root@e7440:/me/media/20230104a# # Let's test the pty system using the script command.
root@e7440:/me/media/20230104a# # the script command will log the shell to its_alive.txt
root@e7440:/me/media/20230104a# script its_alive.txt
Script started, file is its_alive.txt
root@e7440:/me/media/20230104a# ls -lai /dev/pt* # Now after the mount, things have changed!
233300 crw-rw-rw- 1 root root 5, 2 Jan 4 23:08 /dev/ptmx
/dev/pts:
total 4
1 drwxr-xr-x 2 root root 0 Jan 4 23:08 .
229757 drwxr-xr-x 4 root root 4096 Jan 3 14:31 ..
3 crw------- 1 root root 136, 0 Jan 4 23:08 0
2 c--------- 1 root root 5, 2 Jan 4 23:08 ptmx
root@e7440:/me/media/20230104a# # Note the 0 entry! That's the pty we are using to log this with the script command!
root@e7440:/me/media/20230104a# # Also note it is using inode 3 on the devpts file system instance
root@e7440:/me/media/20230104a# # And that it is a 'c' a character device node.
root@e7440:/me/media/20230104a# mount |grep pts
devpts on /dev/pts type devpts (rw)
root@e7440:/me/media/20230104a# umount /dev/pts # Let's go back to no ptys, but wait ...
umount: /dev/pts: target is busy
(In some cases useful info about processes that
use the device is found by lsof(8) or fuser(1).)
root@e7440:/me/media/20230104a# # Naughty! We're using a pty, so we can't get rid of ptys
root@e7440:/me/media/20230104a# exit # We are leaving the script session so its_alive.txt will get closed.
exit
Script done, file is its_alive.txt
root@e7440:/me/media/20230104a# #### Now we can get rid of ptys entirely as no ptys are in use
root@e7440:/me/media/20230104a# ls -lai /dev/pt*
233300 crw-rw-rw- 1 root root 5, 2 Jan 4 23:09 /dev/ptmx
/dev/pts:
total 4
1 drwxr-xr-x 2 root root 0 Jan 4 23:08 .
229757 drwxr-xr-x 4 root root 4096 Jan 3 14:31 ..
2 c--------- 1 root root 5, 2 Jan 4 23:08 ptmx
root@e7440:/me/media/20230104a# ### See no 0 entry (but the /dev/pts/ptmx is there because devpts is mounted)
root@e7440:/me/media/20230104a# mount |grep pts
devpts on /dev/pts type devpts (rw)
root@e7440:/me/media/20230104a# umount /dev/pts
root@e7440:/me/media/20230104a# mount |grep pts
root@e7440:/me/media/20230104a# ls -lai /dev/pt*
233300 crw-rw-rw- 1 root root 5, 2 Jan 4 23:09 /dev/ptmx
/dev/pts:
total 8
237675 drwxr-xr-x 2 root root 4096 Jan 4 23:04 .
229757 drwxr-xr-x 4 root root 4096 Jan 3 14:31 ..
root@e7440:/me/media/20230104a# # Let's see that our session log exists
root@e7440:/me/media/20230104a# ls -l its*
-rwxr-xr-x 1 root root 1025 Jan 4 23:09 its_alive.txt
root@e7440:/me/media/20230104a# # Let's see the session log contents
root@e7440:/me/media/20230104a# grep -n "^" its_alive.txt #Line numbers, please!
1:Script started on Wed Jan 4 23:08:47 2023
2:root@e7440:/me/media/20230104a# ls -lai /dev/pt*
3:233300 crw-rw-rw- 1 root root 5, 2 Jan 4 23:08 /dev/ptmx
4:
5:/dev/pts:
6:total 4
7: 1 drwxr-xr-x 2 root root 0 Jan 4 23:08 .
8:229757 drwxr-xr-x 4 root root 4096 Jan 3 14:31 ..
9: 3 crw------- 1 root root 136, 0 Jan 4 23:08 0
10: 2 c--------- 1 root root 5, 2 Jan 4 23:08 ptmx
11:root@e7440:/me/media/20230104a# # Note the 0 entry! That's the pty we are using to log this with the script command!
12:root@e7440:/me/media/20230104a# mount |grep pts
13:devpts on /dev/pts type devpts (rw)
14:root@e7440:/me/media/20230104a# umount /dev/pts
15:umount: /dev/pts: target is busy
16: (In some cases useful info about processes that
17: use the device is found by lsof(8) or fuser(1).)
18:root@e7440:/me/media/20230104a# # Naughty! We're using a pty
19:root@e7440:/me/media/20230104a# exit
20:exit
21:
22:Script done on Wed Jan 4 23:09:46 2023
root@e7440:/me/media/20230104a# # Yup, life is good!
资料来源:
- https://www.cyberciti.biz/faq/linux-mount-devpts/#:~:text=mount%20-t%20devpts%20devpts%20/dev/pts
- https://en.wikipedia.org/wiki/Devpts
- https://web.archive.org/web/20230105042607/http://faculty.cooper.edu/lent/random/GNU_screen_command.html
- 论文:虚拟终端服务,1987 年,Christopher Lent,库珀科学与艺术促进联盟:Albert Nerken 工程学院