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SSH问题记录

最近经常连国外的服务器,出现了连不上、连上又经常断开的问题。

连不上1

发现卡在:debug1: expecting SSH2_MSG_KEX_ECDH_REPLY上,

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$ ssh -v xxx@47.88.217.222
OpenSSH_7.9p1, LibreSSL 2.7.3
debug1: Reading configuration data /Users/shitaibin/.ssh/config
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 48: Applying options for *
debug1: Connecting to 47.88.217.222 [47.88.217.222] port 22.
debug1: Connection established.
debug1: identity file /Users/shitaibin/.ssh/id_rsa type 0
debug1: identity file /Users/shitaibin/.ssh/id_rsa-cert type -1
debug1: identity file /Users/shitaibin/.ssh/id_dsa type -1
debug1: identity file /Users/shitaibin/.ssh/id_dsa-cert type -1
debug1: identity file /Users/shitaibin/.ssh/id_ecdsa type -1
debug1: identity file /Users/shitaibin/.ssh/id_ecdsa-cert type -1
debug1: identity file /Users/shitaibin/.ssh/id_ed25519 type -1
debug1: identity file /Users/shitaibin/.ssh/id_ed25519-cert type -1
debug1: identity file /Users/shitaibin/.ssh/id_xmss type -1
debug1: identity file /Users/shitaibin/.ssh/id_xmss-cert type -1
debug1: Local version string SSH-2.0-OpenSSH_7.9
debug1: Remote protocol version 2.0, remote software version OpenSSH_7.2p2 Ubuntu-4ubuntu2.4
debug1: match: OpenSSH_7.2p2 Ubuntu-4ubuntu2.4 pat OpenSSH_7.0*,OpenSSH_7.1*,OpenSSH_7.2*,OpenSSH_7.3*,OpenSSH_7.4*,OpenSSH_7.5*,OpenSSH_7.6*,OpenSSH_7.7* compat 0x04000002
debug1: Authenticating to 47.88.217.222:22 as 'nameXXX'
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: algorithm: curve25519-sha256@libssh.org
debug1: kex: host key algorithm: ecdsa-sha2-nistp256
debug1: kex: server->client cipher: chacha20-poly1305@openssh.com MAC: <implicit> compression: none
debug1: kex: client->server cipher: chacha20-poly1305@openssh.com MAC: <implicit> compression: none
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY

Google一下,

  • 原因:MTU太大了,造成了丢包。
  • 方案:把MTU改小,服务器和本机最好都修改,因为无论哪一方的报文再大被丢包都会造成连接失败。
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sudo ifconfig eth0 mtu 1200

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echo "1460" > /sys/class/net/eth0/mtu

连不上2

使用iterm2保存了机器的Profile,连接的时候报错,在本机ssh命令连接正常,错误如下图:

出现: command not found

  • 原因:iterm的profile配置中,Command那项只显示一行,把它ctrl-a全部拷贝出来,发现不仅ssh vnt@47..123,后面还多了2行ip,启动的时候把ip当命令发给服务器,导致出现了此错误。
  • 方案:修改Command只包含ssh命令。

连接断开

都是国外服务器,通信延迟有点高,ping一下,延迟都在300ms以上,经常操作着就卡住了,然后一会报错:packet_write_wait: Broken pipe

  • 原因:通信不好造成连接断开。
  • 方案:加心跳配置。

服务器端或客户端其中一边加就行了,优先加客户端,因为我Mac经常连各种服务器:

文件:~/.ssh/config

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ServerAliveInterval 60

如果服务器被多人连,服务器端也得设置:

文件: /etc/ssh/sshd_config

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ClientAliveInterval 60

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