SSH指定用户登录与限制

环境准备

:::info

实验目标：ServerA通过用户ServerB(已发送密钥和指定端口)

:::

主机	IP	身份
ServerA	192.168.10.201	SSH客户端
ServerB	192.168.10.202	SSH目标主机

在使用SSH登录远程主机时，指定的用户名是指远程主机上的用户。命令格式如下：

ssh username@remote_host

这里的 username 是指您打算用来登录远程目标主机的用户名，这个用户必须存在于远程目标主机的系统中，并且具有相应的访问权限。remote_host 则代表您想要连接的远程服务器的IP地址或域名。

举例来说，如果您要使用名为 myuser 的用户账户登录IP地址为 192.168.0.100 的远程服务器，命令应写作：

ssh myuser@192.168.0.100

在这个命令中：

myuser 是您指定的用户名，对应的是远程服务器上已经存在的用户账户。

192.168.0.100 是远程主机的IP地址

执行此命令后，SSH客户端会尝试使用您本机当前用户的公钥（如果有已配置的密钥对认证）或提示您输入 myuser 账户在远程主机上的密码来进行身份验证。一旦身份验证成功，您将获得 myuser 用户在远程服务器上的 shell 终端会话。

总结来说，通过SSH登录远程主机时指定的用户名是指远程主机上的用户，而不是本机用户。本机用户的信息仅用于确定本地的SSH客户端配置（如私钥位置）以及可能的代理转发设置等，但实际登录远程服务器时的身份是由您提供的远程用户名决定的。

禁止root登录

root登录测试

[root@ServerA ~]# ssh -p 5000 root@ServerB
Activate the web console with: systemctl enable --now cockpit.socket

This system is not registered to Red Hat Insights. See https://cloud.redhat.com/
To register this system, run: insights-client --register

Last failed login: Thu Apr 18 03:59:14 EDT 2024 from 192.168.10.201 on ssh:notty
There was 1 failed login attempt since the last successful login.
Last login: Thu Apr 18 03:56:51 2024 from 192.168.10.201
[root@ServerB ~]# 注销

取消注释改为no

（如果不注销配置则无法生效）

root用户测试

[root@ServerA ~]# ssh -p 5000 root@ServerB
root@serverb's password:
Permission denied, please try again.
root@serverb's password:
Permission denied, please try again.
root@serverb's password:
root@serverb: Permission denied (publickey,gssapi-keyex,gssapi-with-mic,password).

允许禁止某用户登录

远程主机创建用户

[root@Serverb ~]# useradd zhangsan
[root@Serverb ~]# passwd zhangsan
更改用户 zhangsan 的密码 。
新的 密码：
无效的密码： 密码是一个回文
重新输入新的 密码：
passwd：所有的身份验证令牌已经成功更新。
[root@Serverb ~]# useradd lisi
[root@Serverb ~]# passwd lisi
更改用户 lisi 的密码 。
新的 密码：
无效的密码： 密码是一个回文
重新输入新的 密码：
passwd：所有的身份验证令牌已经成功更新。

两个用户都可以远程登录

[root@servera ~]# ssh zhangsan@ServerB -p 5000
zhangsan@serverb's password:
Last login: Fri Jul 12 14:33:34 2024 from servera
[zhangsan@serverb ~]$ exit
logout
Connection to serverb closed.
[root@servera ~]# ssh lisi@ServerB -p 5000
lisi@serverb's password:
Last login: Fri Jul 12 11:24:26 2024 from servera
[lisi@serverb ~]$ exit
logout
Connection to serverb closed.
[root@servera ~]#

底部添加参数允许zhangsan拒绝lisi

[root@Serverb ~]# vim /etc/ssh/sshd_config
[root@Serverb ~]# systemctl restart sshd.service
[root@Serverb ~]# tail -n 3 /etc/ssh/sshd_config
#	ForceCommand cvs server
AllowUsers zhangsan
DenyUsers lisi
[root@Serverb ~]#

测试登录

张三允许登录

[root@servera ~]# ssh zhangsan@ServerB -p 5000
zhangsan@serverb's password:
Last login: Fri Jul 12 14:42:10 2024 from servera
[zhangsan@serverb ~]$ exit
logout
Connection to serverb closed.

李四禁止登录

[root@servera ~]# ssh lisi@ServerB -p 5000
lisi@serverb's password:
Permission denied, please try again.
lisi@serverb's password:
Permission denied, please try again.
lisi@serverb's password:

Pam模块禁止用户

ServerB

只允许李四登录

[root@serverb ~]# echo "lisi" | sudo tee /etc/ssh/allowed_users
lisi
[root@serverb ~]# cat /etc/ssh/allowed_users
lisirverB ~]# chmod 644 /etc/ssh/allowed_users
[root@Serverb ~]# systemctl restart sshd.service
[root@Serverb ~]# tail -n 1 /etc/ssh/sshd_config
#	ForceCommand cvs server
[root@Serverb ~]# tail -n 1 /etc/pam.d/sshd
auth required pam_listfile.so item=user sense=allow onerr=fail file=/etc/ssh/allowed_users

张三禁止登录

[root@servera ~]# ssh zhangsan@ServerB -p 5000
zhangsan@serverb's password:
Permission denied, please try again.
zhangsan@serverb's password:
Permission denied, please try again.
zhangsan@serverb's password:
Permission denied (publickey,gssapi-keyex,gssapi-with-mic,password).

李四可登录

[root@servera ~]# ssh lisi@ServerB -p 5000
lisi@serverb's password:
Last login: Fri Jul 12 14:50:03 2024 from servera

Match User模块

ServerB

使用模块禁止李四

[root@ServerB ~]# vim /etc/ssh/sshd_config
[root@ServerB ~]# tail -n 6 /etc/ssh/sshd_config
#	AllowTcpForwarding no
#	PermitTTY no
#	ForceCommand cvs server
Match User lisi
    PermitTTY no
    ForceCommand /bin/false
[root@ServerB ~]# systemctl restart sshd.service

这里，PermitTTY no禁止分配伪终端，ForceCommand /bin/false设置了一个无效的命令，确保用户无法成功登录。

ServerA

张三用户可登录

[root@servera ~]# ssh zhangsan@ServerB -p 5000
zhangsan@serverb's password:
Last login: Fri Jul 12 15:01:09 2024 from servera
[zhangsan@serverb ~]$ exit
logout
Connection to serverb closed.

李四用户不可登录

[root@servera ~]# ssh lisi@ServerB -p 5000
lisi@serverb's password:
PTY allocation request failed on channel 0
Connection to serverb closed.

指定其他用户免密登录

ServerA

Server通过指定端口将密钥发送到对应用户文件夹下

[root@servera ~]# ssh-copy-id -i .ssh/id_rsa.pub  -p 5000 zhangsan@ServerB
/usr/bin/ssh-copy-id: INFO: Source of key(s) to be installed: ".ssh/id_rsa.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
zhangsan@serverb's password: 

Number of key(s) added: 1

Now try logging into the machine, with:   "ssh -p '5000' 'zhangsan@ServerB'"
and check to make sure that only the key(s) you wanted were added.

ServerB

[root@ServerB ~]# systemctl restart sshd.service
[root@ServerB ~]# ll /home/zhangsan/.ssh/
总用量 4
-rw-------. 1 zhangsan zhangsan 580 4月  18 04:35 authorized_keys
[root@ServerB ~]#

ServerA登录

[root@servera ~]# ssh zhangsan@ServerB -p 5000
Last login: Fri Jul 12 15:05:21 2024 from servera
[zhangsan@serverb ~]$ exit
logout
Connection to serverb closed.

禁止密码登录

PasswordAuthentication no

密码登录测试与免密测试

[root@servera ~]# ssh lisi@ServerB -p 5000
Permission denied (publickey,gssapi-keyex,gssapi-with-mic).
[root@servera ~]# ssh zhangsan@ServerB -p 5000
Last login: Fri Jul 12 15:06:25 2024 from servera
[zhangsan@serverb ~]$ exit
logout
Connection to serverb closed.

指定用户和IP登录

AllowUsers zhangsan@192.168.10.201

拒绝登录

[root@localhost ~]# ifconfig ens160
ens160: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.10.128  netmask 255.255.255.0  broadcast 192.168.10.255
        inet6 fe80::3429:206b:def4:69f2  prefixlen 64  scopeid 0x20<link>
        ether 00:0c:29:be:62:ce  txqueuelen 1000  (Ethernet)
        RX packets 1453  bytes 1745198 (1.6 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 859  bytes 68106 (66.5 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

[root@localhost ~]# ssh zhangsan@192.168.10.202 -p 5000
zhangsan@192.168.10.202's password:
Permission denied, please try again.
zhangsan@192.168.10.202's password:
Permission denied, please try again.
zhangsan@192.168.10.202's password:

允许地址登录

[root@servera ~]# ifconfig ens33
ens33: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.10.201  netmask 255.255.255.0  broadcast 192.168.10.255
        inet6 fe80::c086:7d71:44a8:c234  prefixlen 64  scopeid 0x20<link>
        ether 00:0c:29:9f:70:a6  txqueuelen 1000  (Ethernet)
        RX packets 811  bytes 153103 (149.5 KiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 993  bytes 212878 (207.8 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

[root@servera ~]# ssh zhangsan@ServerB -p 5000
Last failed login: Fri Jul 12 15:58:09 CST 2024 from 192.168.10.128 on ssh:notty
There were 3 failed login attempts since the last successful login.
Last login: Fri Jul 12 15:24:32 2024 from servera
[zhangsan@serverb ~]$