我有两台电脑，一台正在运行Debian GNU/Linux 9和另一个Ubuntu 18.04.1 LTS。我在两台电脑上都安装了openssh。
sudo apt install openssh-client
sudo apt install openssh-server
现在，我可以使用 ssh 从 Debian 连接到 Ubuntu，但不能从 Ubuntu 连接到 Debian。
在 Debian 计算机上
nmap localhost
输出：
Starting Nmap 7.40 ( https://nmap.org ) at 2019-01-24 14:39 CET
Nmap scan report for localhost (127.0.0.1)
Host is up (0.00010s latency).
Other addresses for localhost (not scanned): ::1
Not shown: 999 closed ports
PORT STATE SERVICE
22/tcp open ssh
Nmap done: 1 IP address (1 host up) scanned in 0.04 seconds
我也尝试过跑步
sudo ufw allow ssh
在 Debian 计算机上。
我应该怎么做才能从另一台计算机访问另一台计算机？
已针对评论进行编辑
netstat -l在 Debian 服务器上运行输出：
b1012@debian:~$ netstat -l
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State
tcp 0 0 localhost:5939 0.0.0.0:* LISTEN
tcp 0 0 0.0.0.0:ssh 0.0.0.0:* LISTEN
tcp6 0 0 [::]:ssh [::]:* LISTEN
udp 0 0 0.0.0.0:mdns 0.0.0.0:*
udp 0 0 0.0.0.0:40272 0.0.0.0:*
udp 0 0 0.0.0.0:57967 0.0.0.0:*
udp 0 0 0.0.0.0:bootpc 0.0.0.0:*
udp6 0 0 [::]:mdns [::]:*
udp6 0 0 [::]:41052 [::]:*
raw6 0 0 [::]:ipv6-icmp [::]:* 7
Active UNIX domain sockets (only servers)
Proto RefCnt Flags Type State I-Node Path
unix 2 [ ACC ] STREAM LISTENING 19723 /run/user/1000/pulse/native
unix 2 [ ACC ] STREAM LISTENING 15627 /run/uuidd/request
unix 2 [ ACC ] STREAM LISTENING 15630 /var/run/avahi-daemon/socket
unix 2 [ ACC ] STREAM LISTENING 15633 /var/run/dbus/system_bus_socket
unix 2 [ ACC ] STREAM LISTENING 16129 /tmp/ssh-AYHltf8zzAuv/agent.600
unix 2 [ ACC ] STREAM LISTENING 16960 /tmp/.X11-unix/X0
unix 2 [ ACC ] STREAM LISTENING 18495 /tmp/.ICE-unix/600
unix 2 [ ACC ] STREAM LISTENING 17542 @/tmp/dbus-0nAe1Vft
unix 2 [ ACC ] STREAM LISTENING 16959 @/tmp/.X11-unix/X0
unix 2 [ ACC ] STREAM LISTENING 14138 @/tmp/dbus-kLaALJuH
unix 2 [ ACC ] STREAM LISTENING 18494 @/tmp/.ICE-unix/600
unix 2 [ ACC ] STREAM LISTENING 14179 /run/user/1000/systemd/private
unix 2 [ ACC ] STREAM LISTENING 14184 /run/user/1000/gnupg/S.gpg-agent.browser
unix 2 [ ACC ] STREAM LISTENING 14187 /run/user/1000/bus
unix 2 [ ACC ] STREAM LISTENING 14189 /run/user/1000/gnupg/S.gpg-agent
unix 2 [ ACC ] STREAM LISTENING 14191 /run/user/1000/gnupg/S.gpg-agent.extra
unix 2 [ ACC ] STREAM LISTENING 14193 /run/user/1000/gnupg/S.gpg-agent.ssh
unix 2 [ ACC ] STREAM LISTENING 17539 /run/user/1000/keyring/control
unix 2 [ ACC ] SEQPACKET LISTENING 1427 /run/udev/control
unix 2 [ ACC ] STREAM LISTENING 14139 @/tmp/dbus-kLVeQt6a
unix 2 [ ACC ] STREAM LISTENING 17311 /run/user/1000/keyring/ssh
unix 2 [ ACC ] STREAM LISTENING 17313 /run/user/1000/keyring/pkcs11
unix 2 [ ACC ] STREAM LISTENING 9634 /run/systemd/private
unix 2 [ ACC ] STREAM LISTENING 9648 /run/systemd/journal/stdout
unix 2 [ ACC ] STREAM LISTENING 9653 /run/systemd/fsck.progress
unix 2 [ ACC ] STREAM LISTENING 17541 @/tmp/dbus-yMrL8O3f
unix 2 [ ACC ] STREAM LISTENING 18465 @/tmp/dbus-stZvWk5V9a
unix 2 [ ACC ] STREAM LISTENING 17404 /var/run/NetworkManager/private-dhcp
connection timed out尝试连接时，我得到了。
ssh [email protected] -vvv
OpenSSH_7.6p1 Ubuntu-4ubuntu0.1, OpenSSL 1.0.2n 7 Dec 2017
debug1: Reading configuration data /home/optoscale/.ssh/config
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug2: resolving "192.168.0.104" port 22
debug2: ssh_connect_direct: needpriv 0
debug1: Connecting to 192.168.0.104 [192.168.0.104] port 22.
debug1: connect to address 192.168.0.104 port 22: Connection timed out
ssh: connect to host 192.168.0.104 port 22: Connection timed out
跑步
b1012@debian:~$ systemctl status ssh.service
输出：
● ssh.service - OpenBSD Secure Shell server
Loaded: loaded (/lib/systemd/system/ssh.service; enabled; vendor preset: enab
Active: active (running) since Thu 2019-01-24 13:42:23 CET; 2h 0min ago
Process: 3594 ExecReload=/bin/kill -HUP $MAINPID (code=exited, status=0/SUCCES
Process: 3589 ExecReload=/usr/sbin/sshd -t (code=exited, status=0/SUCCESS)
Main PID: 2332 (sshd)
Tasks: 1 (limit: 4915)
CGroup: /system.slice/ssh.service
└─2332 /usr/sbin/sshd -D
答案1
您的两台计算机之间有 NAT 防火墙。您可以看到这一点，因为您的 Debian 系统的 IP 地址是 192.168.0.24，但 Ubuntu 系统看到来自 10.20.81.24 的关联入站连接。
除非您控制和管理此 NAT 防火墙，否则您将无法直接从 Ubuntu 服务器连接到 Debian 服务器。 （存在多种解决方法，包括autossh在 Debian 系统上运行反向隧道，或者从 Debian 启动到 Ubuntu 的 OpenVPN。两者都可以允许以另一种方式建立连接。）