Linux SSH 服务

本篇写一些关于Linux网络中SSH服务的相关知识。

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测试环境

名称	IP地址
host01	192.168.28.128
host02	192.168.28.129
host03	192.168.28.130

禁止 root 登录

• 查看ssh服务端口是否开启

[root@host01 ~]# netstat -ntuap | grep sshd
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      998/sshd
tcp6       0      0 :::22                   :::*                    LISTEN      998/sshd

• 默认可以使用root用户登录

[root@host02 ~]# ssh root@192.168.28.128
The authenticity of host '192.168.28.128 (192.168.28.128)' can't be established.
ECDSA key fingerprint is SHA256:5GGc1rmzWwjF+ozz/PPTyLO2s6NmFHSxbzCNsLazXhY.
ECDSA key fingerprint is MD5:0b:f5:62:d7:a4:1f:05:64:0b:7f:22:62:11:64:07:61.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '192.168.28.128' (ECDSA) to the list of known hosts.
root@192.168.28.128's password:
Last login: Thu Sep 12 13:54:03 2019
[root@host01 ~]# logout
Connection to 192.168.28.128 closed.

• 编辑配置文件，禁止root用户登录

[root@host01 ~]# vim /etc/ssh/sshd_config
PermitRootLogin no

• 重新加载配置文件，使配置生效

[root@host01 ~]# systemctl reload sshd

• 不可使用root用户登录

[root@host02 ~]# ssh root@192.168.28.128
root@192.168.28.128's password:
Permission denied, please try again.
root@192.168.28.128's password:

• 添加普通用户zhangsan。

[root@host01 ~]# useradd zhangsan && echo "000000" | passwd --stdin zhangsan
Changing password for user zhangsan.
passwd: all authentication tokens updated successfully.
[root@host01 ~]# id zhangsan
uid=1001(zhangsan) gid=1001(zhangsan) groups=1001(zhangsan)

• 现在以zhangsan登录，发现可以切换至root用户

[root@host02 ~]# ssh zhangsan@192.168.28.128
zhangsan@192.168.28.128's password:
[zhangsan@host01 ~]$ su - root
Password:
Last login: Thu Sep 12 14:43:14 CST 2019 from 192.168.28.129 on pts/2
Last failed login: Thu Sep 12 14:46:39 CST 2019 from 192.168.28.129 on ssh:notty
There was 1 failed login attempt since the last successful login.
[root@host01 ~]# logout
[zhangsan@host01 ~]$ logout
Connection to 192.168.28.128 closed.

• 可以开启pam认证来禁止切换

[root@host01 ~]# vim /etc/pam.d/su
auth            required        pam_wheel.so use_uid

• 现在不可以使用zhangsan做跳板切换至root用户

[root@host02 ~]# ssh zhangsan@192.168.28.128
zhangsan@192.168.28.128's password:
Last login: Thu Sep 12 14:56:01 2019 from 192.168.28.129
[zhangsan@host01 ~]$ su - root
Password:
su: Permission denied
[zhangsan@host01 ~]$ logout
Connection to 192.168.28.128 closed.

• 将zhangsan添加至wheel组

[root@host01 ~]# gpasswd -a zhangsan wheel
Adding user zhangsan to group wheel
[root@host01 ~]# id zhangsan
uid=1001(zhangsan) gid=1001(zhangsan) groups=1001(zhangsan),10(wheel)

• 只有在wheel组中的用户才可以使用su命令

[root@host02 ~]# ssh zhangsan@192.168.28.128
zhangsan@192.168.28.128's password:
Last login: Thu Sep 12 14:59:14 2019 from 192.168.28.129
[zhangsan@host01 ~]$ su - root
Password:
Last login: Thu Sep 12 14:56:13 CST 2019 on pts/2
Last failed login: Thu Sep 12 14:59:25 CST 2019 on pts/2
There was 1 failed login attempt since the last successful login.
[root@host01 ~]# logout
[zhangsan@host01 ~]$ logout
Connection to 192.168.28.128 closed.

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登录次数尝试

• 配置文件默认是6次，但尝试3次就不可再尝试

[root@host02 ~]# ssh zhangsan@192.168.28.128
zhangsan@192.168.28.128's password:
Permission denied, please try again.
zhangsan@192.168.28.128's password:
Permission denied, please try again.
zhangsan@192.168.28.128's password:
Permission denied (publickey,gssapi-keyex,gssapi-with-mic,password).

• 设置参数最大次数为5次

[root@host01 ~]# vim /etc/ssh/sshd_config
MaxAuthTries 5

• 重新加载配置文件，使配置生效

[root@host01 ~]# systemctl reload sshd

• 想要使配置能够有意义，需要使用-o NumberOfPasswordPrompts=8参数，这里尝试8次，发现5次后被拒绝尝试。

[root@host02 ~]# ssh -o NumberOfPasswordPrompts=8 zhangsan@192.168.28.128
zhangsan@192.168.28.128's password:
Permission denied, please try again.
zhangsan@192.168.28.128's password:
Permission denied, please try again.
zhangsan@192.168.28.128's password:
Permission denied, please try again.
zhangsan@192.168.28.128's password:
Permission denied, please try again.
zhangsan@192.168.28.128's password:
Received disconnect from 192.168.28.128 port 22:2: Too many authentication failures
Authentication failed.

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黑白名单

• 添加lisi、wangwu用户

[root@host01 ~]# useradd lisi && echo "000000" | passwd --stdin lisi
Changing password for user lisi.
passwd: all authentication tokens updated successfully.
[root@host01 ~]# useradd wangwu && echo "000000" | passwd --stdin wangwu
Changing password for user wangwu.
passwd: all authentication tokens updated successfully.

• 添加白名单配置，默认没有相关条目zhangsan只能从129登录，lisi可以从任何主机登录

[root@host01 ~]# vim /etc/ssh/sshd_config
AllowUsers zhangsan@192.168.28.129 lisi

白名单：AllowUsers，黑名单：DenyUsers，不要同时使用。

• 重新加载配置文件，使配置生效

[root@host01 ~]# systemctl reload sshd

• 测试zhangsan可以从129登录

[root@host02 ~]# ssh zhangsan@192.168.28.128
zhangsan@192.168.28.128's password:
Last login: Thu Sep 12 16:53:09 2019 from 192.168.28.129
[zhangsan@host01 ~]$ logout
Connection to 192.168.28.128 closed.

• 测试lisi可以从129登录

[root@host02 ~]# ssh lisi@192.168.28.128
lisi@192.168.28.128's password:
[lisi@host01 ~]$ logout
Connection to 192.168.28.128 closed.

• 测试wangwu不可从129登录

[root@host02 ~]# ssh wangwu@192.168.28.128
wangwu@192.168.28.128's password:
Permission denied, please try again.
wangwu@192.168.28.128's password:

• 测试zhangsan不可从130登录

[root@host03 ~]# ssh zhangsan@192.168.28.128
zhangsan@192.168.28.128's password:
Permission denied, please try again.
zhangsan@192.168.28.128's password:

• 测试lisi可以从130登录

[root@host03 ~]# ssh lisi@192.168.28.128
lisi@192.168.28.128's password:
Last login: Thu Sep 12 16:56:07 2019 from 192.168.28.129
[lisi@host01 ~]$ logout
Connection to 192.168.28.128 closed.

• 测试wangwu不可从130登录

[root@host03 ~]# ssh wangwu@192.168.28.128
wangwu@192.168.28.128's password:
Permission denied, please try again.
wangwu@192.168.28.128's password:

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使用密钥对登录

• 开启密钥认证选项

[root@host01 ~]# vim /etc/ssh/sshd_config
PubkeyAuthentication yes

• 重新加载配置文件，使配置生效

[root@host01 ~]# systemctl reload sshd

• 生成类型为ecdsa椭圆曲线数字签名加密的密钥，可以设置一个密码

[root@host02 ~]# ssh-keygen -t 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:
SHA256:Y4AjDPfBRwYAP5exUlv7Obn08cvhSZzAsZ6Mwqt/ccE root@host02
The key's randomart image is:
+---[ECDSA 256]---+
|o.oo=o+          |
| = o.X..         |
|  * O.o  ..      |
|   = . o +Eo     |
|        S =.     |
|     . o.O.* .   |
|      o oo= *    |
|       o.  + +   |
|    .oo.    =    |
+----[SHA256]-----+

• 查看生成的私钥和公钥文件

[root@host02 ~]# ls .ssh/
id_ecdsa  id_ecdsa.pub

• 推送公钥文件至128的lisi用户

[root@host02 ~]# ssh-copy-id -i .ssh/id_ecdsa.pub lisi@192.168.28.128
/usr/bin/ssh-copy-id: INFO: Source of key(s) to be installed: ".ssh/id_ecdsa.pub"
/usr/bin/ssh-copy-id: INFO: attempting to log in with the new key(s), to filter out any that are already installed
/usr/bin/ssh-copy-id: INFO: 1 key(s) remain to be installed -- if you are prompted now it is to install the new keys
lisi@192.168.28.128's password: 

Number of key(s) added: 1

Now try logging into the machine, with:   "ssh 'lisi@192.168.28.128'"
and check to make sure that only the key(s) you wanted were added.

• 本地会生成一个已知主机文件

[root@host02 ~]# ls .ssh/
id_ecdsa  id_ecdsa.pub  known_hosts

• 可以查看一下

[root@host02 ~]# cat .ssh/known_hosts
192.168.28.128 ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBG/cLQC3IgLKJnuYS8mOuhuJjfnMT4V2CsSJ6GNFgBlmANrik1sLgUeSIfyPOeirGfyz0En3/AAyI+slLpA/3lQ=

• 128的lisi用户下生成了认证密钥

[root@host01 ~]# cat /home/lisi/.ssh/authorized_keys
ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBEE/8T2xbTo11fmJu5sAc43OyUELuvl6OvcEiJ4WrZxaD9QR+PmJCxLZoVd5+HwyT6PFmW7EZjMk8NogcnDc9HI= root@host02

• 使用128的lisi用户ssh登录，提示输入先前设置的密码

[root@host02 ~]# ssh lisi@192.168.28.128
Enter passphrase for key '/root/.ssh/id_ecdsa':
Last login: Thu Sep 12 17:09:37 2019 from 192.168.28.129
[lisi@host01 ~]$ logout
Connection to 192.168.28.128 closed.

• 可以设置免验证操作，并输入先前设置的密码

[root@host02 ~]# ssh-agent bash
[root@host02 ~]# ssh-add
Enter passphrase for /root/.ssh/id_ecdsa:
Identity added: /root/.ssh/id_ecdsa (/root/.ssh/id_ecdsa)

• 现在可以免密码登录

[root@host02 ~]# ssh lisi@192.168.28.128
Last login: Tue Sep 17 00:40:47 2019 from 192.168.28.129
[lisi@host01 ~]$ logout
Connection to 192.168.28.128 closed.

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更改默认端口

• 关闭防火墙、SELinux。

[root@host01 ~]# systemctl stop firewalld
[root@host01 ~]# setenforce 0

• 更改默认端口22为2233

[root@host01 ~]# vim /etc/ssh/sshd_config
Port 2233

• 重新加载配置文件，使配置生效

[root@host01 ~]# systemctl reload sshd
[root@host01 ~]# netstat -ntuap | grep sshd
tcp        0      0 0.0.0.0:2233            0.0.0.0:*               LISTEN      41357/sshd
tcp6       0      0 :::2233                 :::*                    LISTEN      41357/sshd

• 直接登录失败

[root@host02 ~]# ssh lisi@192.168.28.128
ssh: connect to host 192.168.28.128 port 22: Connection refused

• 指定端口登录成功

[root@host02 ~]# ssh -p 2233 lisi@192.168.28.128
Last login: Tue Sep 17 01:21:11 2019 from 192.168.28.129
[lisi@host01 ~]$ logout
Connection to 192.168.28.128 closed.

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scp 远程复制

• 创建测试文件、文件夹

[root@host02 ~]# echo "this is testfile01" > testfile01.txt
[root@host02 ~]# mkdir testdir01

• 远程复制文件

[root@host02 ~]# scp testfile01.txt root@192.168.28.128:/opt/
root@192.168.28.128's password:
testfile01.txt                                                                                                                                             100%   19    11.4KB/s   00:00

• 远程复制文件夹

[root@host02 ~]# scp -r testdir01/ root@192.168.28.128:/opt/
root@192.168.28.128's password:

• 查看是否复制成功

[root@host01 ~]# ls /opt/
rh  testdir01  testfile.txt

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sftp 安全文件传输协议

• 登录

[root@host02 ~]# sftp root@192.168.28.128
root@192.168.28.128's password:
Connected to 192.168.28.128.
sftp>

• 可以cd切换目录，ls查看，put上传

sftp> cd /home/zhangsan/
sftp> ls
sftp> put /root/testfile01.txt
Uploading /root/testfile01.txt to /home/zhangsan/testfile01.txt
/root/testfile01.txt                                                                                                                                       100%   19    32.8KB/s   00:00
sftp> ls
testfile01.txt

• 上传成功

[root@host01 ~]# ls /home/zhangsan/
testfile01.txt

• get下载

sftp> get /etc/passwd
Fetching /etc/passwd to passwd
/etc/passwd                                                                                                                                                100% 2227     1.8MB/s   00:00
sftp> bye

• 下载成功

[root@host02 ~]# ls
anaconda-ks.cfg  passwd  testdir01  testfile01.txt