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在docker中開啟sshd操作

首先在docker中安裝openssh-server,安裝完畢后切換到openssh-server的安裝目錄/etc/ssh下面。

運行ssh-keygen生成對應的密鑰。

先看看sshd的配置文件sshd_config，里面有如下內容：

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，根據這幾種加密方式來生成對應的密鑰對。

[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

密鑰對生成完畢后，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

運行/usr/sbin/sshd,查看22端口號是否開啟，開啟說明啟動成功。

[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)

補充知識：Docker容器內運行sshd進程，遠程登錄閃退(Exit status 254)

注：

背景

在容器內運行了一個sshd進程，映射出一個端口供外部遠程連接。可以每次連接的時候，輸入密碼后立即就退出了，現象如下：

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

查看調試信息，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

從打印來看，已經有Last login的信息，所以密碼肯定是輸入正確的，也已經登錄系統，那就是在初始化的環境的時候跪了。首先考慮了hosts.deny的配置，注釋相關配置后問題依舊。

網上有說注釋sshd配置文件中的UsePAM配置，也就是不使用pam鑒權模塊，

#UsePAM yes

修改完重啟sshd進程，這下果然可以了。至于原因，清一色的說是什么默認配置下，啟用了超時斷開連接功能。這就是在扯，默認的鏈接斷開時間不可能這么短，而且為什么在非docker環境下sshd進程運行是正常的。我是不接受這個理由的。那就再看看唄。不使用pam鑒權就沒問題，于是又挨個把/etc/pam.d/里和sshd相關的配置一個一個注釋，還是沒發現問題所在。

這時想到可以看看pam的日志，應該有些提示吧。順帶提一下， RedHat和CentOS的pam日志存放在/var/log/secure中，Ubuntu和Debian在 /var/log/auth.log中存儲認證信息。

果然，pam里有錯誤信息，

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

可見，這是由于設置nproc、nofile、memlock等參數權限不夠而導致，而這些配置是在pam組件里，由以下兩個文件保存配置，