由于缺少 /var/run/sshd，SSH 服务器在重新启动后停止工作

Question

我的 VPS 大约 3 个月没有重新启动。它托管在 OpenVZ 虚拟化类型的服务器上，操作系统为 Ubuntu 16.04。出于某种原因，我重新启动了 VPS，之后，我无法通过 ssh 连接到服务器，我收到的消息是：

ssh: connect to host srvname.com port 22: Connection refused

所以我在 VPS 上打开了一个串行控制台并开始调查......我已经清除并重新安装了但openssh-server没有成功。我花了两个小时阅读有关 Internet 上类似问题的文章、问题和答案。

最后我设法理解该目录/var/run/sshd不是在系统启动期间创建的。一旦我手动创建它，我就可以毫无问题地启动 SSH 服务，但是在下次重新启动时问题仍然存在。所以我的问题是：

• 这个问题的原因可能是什么？为什么/var/run/sshd在系统启动时没有创建？

• 我怎样才能以正确的方式解决问题？我找到了本文末尾提到的临时解决方案。

• 问题是否可能与 VPS 的 OpenVZ 主机有关？我应该要求托管服务提供商解决吗？

---

的输出systemctl status ssh.service，sshd -Ddp 22并且journalctl -xe是：

ssh: connect to host srvname.com port 22: Connection refused

的内容/usr/lib/tmpfiles.d/sshd.conf和/etc/init/ssh.conf为：

# systemctl status ssh.service
? ssh.service - OpenBSD Secure Shell server
   Loaded: loaded (/lib/systemd/system/ssh.service; enabled; vendor preset: enabled)
   Active: failed (Result: start-limit-hit) since ?? 2019-01-15 12:58:08 EET; 22s ago
  Process: 407 ExecStartPre=/usr/sbin/sshd -t (code=exited, status=255)

??? 15 12:58:07 srvname systemd[1]: Failed to start OpenBSD Secure Shell server.
??? 15 12:58:07 srvname systemd[1]: ssh.service: Unit entered failed state.
??? 15 12:58:07 srvname systemd[1]: ssh.service: Failed with result 'exit-code'.
??? 15 12:58:08 srvname systemd[1]: ssh.service: Service hold-off time over, scheduling restart.
??? 15 12:58:08 srvname systemd[1]: Stopped OpenBSD Secure Shell server.
??? 15 12:58:08 srvname systemd[1]: ssh.service: Start request repeated too quickly.
??? 15 12:58:08 srvname systemd[1]: Failed to start OpenBSD Secure Shell server.
??? 15 12:58:08 srvname systemd[1]: ssh.service: Unit entered failed state.
??? 15 12:58:08 srvname systemd[1]: ssh.service: Failed with result 'start-limit-hit'.


# $(which sshd) -Ddp 22
debug1: sshd version OpenSSH_7.2, OpenSSL 1.0.2g  1 Mar 2016
debug1: private host key #0: ssh-rsa SHA256:...
debug1: private host key #1: ssh-dss SHA256:...
debug1: private host key #2: ecdsa-sha2-nistp256 SHA256:...
debug1: private host key #3: ssh-ed25519 SHA256:...
Missing privilege separation directory: /var/run/sshd


# journalctl -xe
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit ssh.service has begun starting up.
??? 15 13:21:21 srvname sshd[1688]: Missing privilege separation directory: /var/run/sshd
??? 15 13:21:21 srvname systemd[1]: ssh.service: Control process exited, code=exited status=255
??? 15 13:21:21 srvname systemd[1]: Failed to start OpenBSD Secure Shell server.
-- Subject: Unit ssh.service has failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit ssh.service has failed.
-- 
-- The result is failed.
??? 15 13:21:21 srvname systemd[1]: ssh.service: Unit entered failed state.
??? 15 13:21:21 srvname systemd[1]: ssh.service: Failed with result 'exit-code'.
??? 15 13:21:22 srvname systemd[1]: ssh.service: Service hold-off time over, scheduling restart.
??? 15 13:21:22 srvname systemd[1]: Stopped OpenBSD Secure Shell server.
-- Subject: Unit ssh.service has finished shutting down
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit ssh.service has finished shutting down.
??? 15 13:21:22 srvname systemd[1]: Starting OpenBSD Secure Shell server...
-- Subject: Unit ssh.service has begun start-up
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit ssh.service has begun starting up.
??? 15 13:21:22 srvname sshd[1691]: Missing privilege separation directory: /var/run/sshd
??? 15 13:21:22 srvname systemd[1]: ssh.service: Control process exited, code=exited status=255
??? 15 13:21:22 srvname systemd[1]: Failed to start OpenBSD Secure Shell server.
-- Subject: Unit ssh.service has failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit ssh.service has failed.
-- 
-- The result is failed.
??? 15 13:21:22 srvname systemd[1]: ssh.service: Unit entered failed state.
??? 15 13:21:22 srvname systemd[1]: ssh.service: Failed with result 'exit-code'.
??? 15 13:21:22 srvname systemd[1]: ssh.service: Service hold-off time over, scheduling restart.
??? 15 13:21:22 srvname systemd[1]: Stopped OpenBSD Secure Shell server.
-- Subject: Unit ssh.service has finished shutting down
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit ssh.service has finished shutting down.
??? 15 13:21:22 srvname systemd[1]: ssh.service: Start request repeated too quickly.
??? 15 13:21:22 srvname systemd[1]: Failed to start OpenBSD Secure Shell server.
-- Subject: Unit ssh.service has failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit ssh.service has failed.
-- 
-- The result is failed.
??? 15 13:21:22 srvname systemd[1]: ssh.service: Unit entered failed state.
??? 15 13:21:22 srvname systemd[1]: ssh.service: Failed with result 'start-limit-hit'.

有关系统的其他信息：

# cat /usr/lib/tmpfiles.d/sshd.conf 
d /var/run/sshd 0755 root root

# cat /etc/init/ssh.conf | sed '/^#/ d'

description "OpenSSH server"

start on runlevel [2345]
stop on runlevel [!2345]

respawn
respawn limit 10 5
umask 022

env SSH_SIGSTOP=1
expect stop

console none

pre-start script
    test -x /usr/sbin/sshd || { stop; exit 0; }
    test -e /etc/ssh/sshd_not_to_be_run && { stop; exit 0; }

    mkdir -p -m0755 /var/run/sshd
end script

exec /usr/sbin/sshd -D

---

临时解决方案： 我发现这/var/run是一个指向 的符号链接/run，我不知道为什么需要这样做，但是当我/usr/lib/tmpfiles.d/sshd.conf从以下位置修改文件内容时：

# lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 16.04.5 LTS
Release:    16.04
Codename:   xenial

# uname -a
Linux srvname 2.6.32-042stab127.2 #1 SMP Thu Jan 4 16:41:44 MSK 2018 x86_64 x86_64 x86_64 GNU/Linux

# apt show openssh-server | grep 'Version'
Version: 1:7.2p2-4ubuntu2.6

到：

d /var/run/sshd 0755 root root

系统启动一切正常，SSH服务正常启动，我可以通过SSH登录。

Answer 1

我发现这是当前版本的 systemd 和一些 VPS privdes 使用的旧内核的错误，就像我的情况一样。这个错误不时出现，正如我们在 Launchpad 上看到的：Bug #45234，Bug #1811580；或在 ServerFault 上：为什么每次启动后我都缺少 /var/run/sshd？

这个问题的解决方法很少，它们都聚集在一起，/var/run/sshd在运行 SSH 服务器之前创建替代方法。以下是三种可能的解决方案。

解决方法一：修改/usr/lib/tmpfiles.d/sshd.conf如下：

d /run/sshd 0755 root root

正如问题中提到的那样，/var/run是到 的符号链接/run，最终结果是相同的：/var/run/sshd被创建。我不知道为什么，但这有效。

解决方法 2：使用将创建/var/run/sshd并重新启动 SSH 服务器的Cron 作业，您可以crontab为此使用 root 用户- 执行sudo crontab -e并添加以下条目：

@reboot mkdir -p -m0755 /var/run/sshd && systemctl restart ssh.service

目前我正在使用这个解决方案，所以它也经过了测试。

解决方法3：用/etc/rc.local做与上述相同，因为它是在此评论中所示的错误报告＃45234。

Answer 2

您能否检查您的/（根文件系统）权限是否未更改？必须root:root像下面的两行：

drwxr-xr-x  25 root root      4096 ??? 21 06:45 ..
drwxr-xr-x  25 root root      4096 ??? 21 06:45 .

如果所有者是另一个用户（而不是 root），这将阻止 systemd 在系统启动期间创建所有临时文件。您也可以使用以下命令进行检查：

systemd-tmpfiles --create

如果根文件夹 ( /) 具有不同的权限，请使用以下命令进行更改：

chown root: /