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 ~]$
