# linux互相登陆

linux中的用户登陆时基于sshd服务的，安装openssh

```bash
[root@localhost ~]# yum install openssh-server openssh openssh-clients
已加载插件：fastestmirror
Loading mirror speeds from cached hostfile
 * base: mirrors.cqu.edu.cn
 * extras: mirrors.cqu.edu.cn
 * updates: mirrors.cqu.edu.cn
软件包 openssh-server-7.4p1-16.el7.x86_64 已安装并且是最新版本
软件包 openssh-7.4p1-16.el7.x86_64 已安装并且是最新版本
软件包 openssh-clients-7.4p1-16.el7.x86_64 已安装并且是最新版本
无须任何处理
[root@localhost ~]# systemctl restart sshd
[root@localhost ~]# netstat -tnlp
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name    
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      1361/sshd           
tcp        0      0 127.0.0.1:25            0.0.0.0:*               LISTEN      1056/master         
tcp6       0      0 :::22                   :::*                    LISTEN      1361/sshd           
tcp6       0      0 ::1:25                  :::*                    LISTEN      1056/master
```

使用ssh命令登陆(ssh username\@ip \[-p port]])：

> 注意需要关闭linux下的防火墙

```bash
[root@localhost ~]# systemctl stop firewalld # 关闭linux防火墙
[root@localhost ~]# setenforce 0 # 关闭linux安全软件
setenforce: SELinux is disabled
[root@localhost ~]# ssh root@192.168.127.128 -p 22
The authenticity of host '192.168.127.128 (192.168.127.128)' can't be established.
ECDSA key fingerprint is SHA256:JLkdVkJFdosZSNG+/PTRObRm3MvwHP3q0aZoSm9kAGk.
ECDSA key fingerprint is MD5:ec:8e:50:11:b3:b9:32:22:fe:4a:4c:1b:75:23:ac:71.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '192.168.127.128' (ECDSA) to the list of known hosts.
root@192.168.127.128's password: 
Last login: Sat Aug  4 16:16:11 2018 from 192.168.127.1
```

这样登陆需要密码，我们可以使用密钥登陆：

```bash
[root@localhost ~]# ssh-keygen # 创建密钥
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa): 
Created directory '/root/.ssh'.
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:
SHA256:ufhYNTlyQv7C3sLvhGUs1kLIgsrQ14Iim+59wAn7onU root@localhost.localdomain
The key's randomart image is:
+---[RSA 2048]----+
|                 |
| . o o .         |
|+ + + + o        |
|+* . o + + .     |
|+.+ .   S @      |
|.. +   + & o     |
| .o E ..* o      |
|.o.o . =o+       |
|o.... . o++      |
+----[SHA256]-----+
[root@localhost ~]# ssh-copy-id root@192.168.127.128 # 上传到需要密钥登陆的服务器
/usr/bin/ssh-copy-id: INFO: Source of key(s) to be installed: "/root/.ssh/id_rsa.pub"
The authenticity of host '192.168.127.128 (192.168.127.128)' can't be established.
ECDSA key fingerprint is SHA256:JLkdVkJFdosZSNG+/PTRObRm3MvwHP3q0aZoSm9kAGk.
ECDSA key fingerprint is MD5:ec:8e:50:11:b3:b9:32:22:fe:4a:4c:1b:75:23:ac:71.
Are you sure you want to continue connecting (yes/no)? yes
/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
root@192.168.127.128's password: 

Number of key(s) added: 1

Now try logging into the machine, with:   "ssh 'root@192.168.127.128'"
and check to make sure that only the key(s) you wanted were added.

[root@localhost ~]# ssh root@192.168.127.128 # 直接登陆
Last failed login: Sat Aug  4 17:23:57 CST 2018 from 192.168.127.128 on ssh:notty
There was 1 failed login attempt since the last successful login.
Last login: Sat Aug  4 17:20:47 2018 from 192.168.127.128
[root@localhost ~]#
```


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