在docker中开启sshd操作

原作者: [db:作者] 来自: [db:来源] 收藏邀请

首先在docker中安装openssh-server,安装完毕后切换到openssh-server的安装目录/etc/ssh下面。

运行ssh-keygen生成对应的密钥。

先看看sshd的配置文件sshd_config，里面有如下内容：

HostKey /etc/ssh/ssh_host_rsa_key
#HostKey /etc/ssh/ssh_host_dsa_key
HostKey /etc/ssh/ssh_host_ecdsa_key
HostKey /etc/ssh/ssh_host_ed25519_key

有rsa,dsa,ecdsa,ed25519的加密方式，根据这几种加密方式来生成对应的密钥对。

[root@655f62a4ed82 ssh]# ssh-keygen -t rsa //生成rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa): 
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /root/.ssh/id_rsa.
Your public key has been saved in /root/.ssh/id_rsa.pub.
The key fingerprint is:
0e:fa:07:36:bb:87:c1:60:14:be:41:41:01:1b:4b:bc root@655f62a4ed82
The key's randomart image is:
+--[ RSA 2048]----+
| .+o*+      |
| ..*.      |
| ooo      |
| E oo      |
|  ..o. S    |
|   .*o     |
|  .. *.    |
|   .o o    |
|   o+     |
+-----------------+
[root@655f62a4ed82 ssh]# ssh-keygen -t dsa //生成dsa
Generating public/private dsa key pair.
Enter file in which to save the key (/root/.ssh/id_dsa): 
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /root/.ssh/id_dsa.
Your public key has been saved in /root/.ssh/id_dsa.pub.
The key fingerprint is:
ee:8c:db:a8:24:68:0d:33:79:eb:09:33:ed:74:c3:66 root@655f62a4ed82
The key's randomart image is:
+--[ DSA 1024]----+
|         |
|         |
|         |
| .       |
| = .  S    |
| .B o .     |
|.=.=.E .    |
|. Bo= .*     |
|  +..+.+    |
+-----------------+
[root@655f62a4ed82 ssh]# ssh-keygen -t ecdsa //生成ecdsa
Generating public/private ecdsa key pair.
Enter file in which to save the key (/root/.ssh/id_ecdsa): 
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /root/.ssh/id_ecdsa.
Your public key has been saved in /root/.ssh/id_ecdsa.pub.
The key fingerprint is:
84:74:de:d1:e4:98:a1:5c:27:25:8e:b7:d6:27:fd:c9 root@655f62a4ed82
The key's randomart image is:
+--[ECDSA 256]---+
|   . . *++  |
|   . = * X.  |
|   . * * .  |
|    . . o .  |
|    S o o o |
|     .  o...|
|        E.|
|         |
|         |
+-----------------+
[root@655f62a4ed82 ssh]# ssh-keygen -t ed25519
Generating public/private ed25519 key pair.
Enter file in which to save the key (/root/.ssh/id_ed25519): 
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /root/.ssh/id_ed25519.
Your public key has been saved in /root/.ssh/id_ed25519.pub.
The key fingerprint is:
d8:40:95:1f:07:96:8a:83:7f:af:19:01:3b:b4:79:91 root@655f62a4ed82
The key's randomart image is:
+--[ED25519 256--+
|   ....oo   |
|   . .oo .  |
|   .+.Eo o   |
|  ..oO...   |
|   .*.S    |
|   .o..    |
|    ...    |
|     o.   |
|    o.    |
+-----------------+
[root@655f62a4ed82 ssh]# cp ~/.ssh/id_rsa.pub ~/.ssh/authorized_keys

密钥对生成完毕后，需要修改sshd_config中上述文件所在的位置的。

HostKey /root/.ssh/id_rsa
HostKey /root/.ssh/id_dsa
HostKey /root/.ssh/id_ecdsa
HostKey /root/.ssh/id_ed25519

运行/usr/sbin/sshd,查看22端口号是否开启，开启说明启动成功。

[root@655f62a4ed82 ssh]# /usr/sbin/sshd
[root@655f62a4ed82 ssh]# lsof -i:22
COMMAND PID USER  FD  TYPE DEVICE SIZE/OFF NODE NAME
sshd   37 root  3u IPv4 250907   0t0 TCP *:ssh (LISTEN)
sshd   37 root  4u IPv6 250909   0t0 TCP *:ssh (LISTEN)

补充知识：Docker容器内运行sshd进程，远程登录闪退(Exit status 254)

注：

背景

在容器内运行了一个sshd进程，映射出一个端口供外部远程连接。可以每次连接的时候，输入密码后立即就退出了，现象如下：

[root@localhost /]# ssh [email protected] -p 8000
[email protected]'s password: 
Last login: Tue Nov 6 14:46:17 2018 from 192.168.0.6
Connection to 192.168.0.6 closed.

查看调试信息，最后退出的打印如下：

......
Connection to 192.168.0.6 closed.
Transferred: sent 2264, received 2224 bytes, in 0.0 seconds
Bytes per second: sent 235367.6, received 231209.1
debug1: Exit status 254

分析

从打印来看，已经有Last login的信息，所以密码肯定是输入正确的，也已经登录系统，那就是在初始化的环境的时候跪了。首先考虑了hosts.deny的配置，注释相关配置后问题依旧。

网上有说注释sshd配置文件中的UsePAM配置，也就是不使用pam鉴权模块，

#UsePAM yes

修改完重启sshd进程，这下果然可以了。至于原因，清一色的说是什么默认配置下，启用了超时断开连接功能。这就是在扯，默认的链接断开时间不可能这么短，而且为什么在非docker环境下sshd进程运行是正常的。我是不接受这个理由的。那就再看看呗。不使用pam鉴权就没问题，于是又挨个把/etc/pam.d/里和sshd相关的配置一个一个注释，还是没发现问题所在。

这时想到可以看看pam的日志，应该有些提示吧。顺带提一下， RedHat和CentOS的pam日志存放在/var/log/secure中，Ubuntu和Debian在 /var/log/auth.log中存储认证信息。

果然，pam里有错误信息，

Nov 6 15:36:56 bbb sshd[11016]: Accepted password for root from 192.168.0.6 port 56394 ssh2
Nov 6 15:36:56 bbb sshd[11016]: pam_limits(sshd:session): Could not set limit for 'nproc': Operation not permitted
Nov 6 15:36:56 bbb sshd[11016]: pam_limits(sshd:session): Could not set limit for 'nofile': Operation not permitted
Nov 6 15:36:56 bbb sshd[11016]: pam_limits(sshd:session): Could not set limit for 'memlock': Operation not permitted
Nov 6 15:36:56 bbb sshd[11016]: pam_unix(sshd:session): session opened for user root by (uid=0)
Nov 6 15:36:56 bbb sshd[11016]: error: PAM: pam_open_session(): Permission denied
Nov 6 15:36:56 bbb sshd[11016]: Received disconnect from 192.168.0.6: 11: disconnected by user

可见，这是由于设置nproc、nofile、memlock等参数权限不够而导致，而这些配置是在pam组件里，由以下两个文件保存配置，