Ssh
ssh 只有一種方式
我有兩台電腦，一台執行Debian GNU/Linux 9，另一台執行Ubuntu 18.04.1 LTS。我在兩台電腦上都安裝了 openssh。
sudo apt install openssh-client sudo apt install openssh-server現在，我可以使用 ssh 從 Debian 連接到 Ubuntu，但不能從 Ubuntu 連接到 Debian。
在 Debian 電腦上
nmap localhost輸出：
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我也試過跑步
sudo ufw allow ssh在 Debian 電腦上。
我應該怎麼做才能從另一台電腦訪問任何一台電腦？
根據評論編輯
netstat -l在 debian 伺服器上執行輸出：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嘗試連接時，我得到了。ssh b1012@192.168.0.104 -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輸出：
● 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
你的兩台機器之間有一個 NAT 防火牆。您可以看到這一點，因為您的 Debian 系統的 IP 地址是 192.168.0.24，但 Ubuntu 系統看到相關的入站連接來自 10.20.81.24。
除非您控制和管理此 NAT 防火牆，否則您不可能直接從 Ubuntu 伺服器連接到 Debian 伺服器。（存在各種變通方法，包括
autossh在您的 Debian 系統上使用反向隧道執行，或者從 Debian 到 Ubuntu 啟動 OpenVPN。兩者都可以允許以另一種方式重新建立連接。）