ssh

install

archlinux

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pacman -S openssh

ubuntu

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sudo apt-get install openssh-server
sudo apt-get install openssh-client

commands

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# 超时时间
ssh -o ConnectTimeout=10  <hostName>
# -o, option

Ubuntu缺省安装了openssh-client,所以在这里就不安装了，如果你的系统没有安装的话，再用apt-get安装上即可。

然后确认sshserver是否启动了:

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ps -e |grep ssh

如果只有ssh-agent那ssh-server还没有启动，需要/etc/init.d/ssh start，如果看到sshd那说明ssh-server已经启动了。

ssh-server配置文件位于/ etc/ssh/sshd_config，在这里可以定义SSH的服务端口，默认端口是22，你可以自己定义成其他端口号，如222。然后重启SSH服务:

sudo /etc/init.d/ssh resar

no matching host key type found. Their offer: ssh-rsa

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ssh -o HostKeyAlgorithms=+ssh-rsa -o PubkeyAcceptedKeyTypes=+ssh-rsa  root@192.168.50.1 -p 22
ssh -o HostKeyAlgorithms=+ssh-rsa -o PubkeyAcceptedKeyTypes=+ssh-rsa  root@192.168.50.4 -p 22

为什么会有这个错误根据 OpenSSH Release Notes

Future deprecation notice

It is now possible[1] to perform chosen-prefix attacks against the SHA-1 algorithm for less than USD$50K.

In the SSH protocol, the “ssh-rsa” signature scheme uses the SHA-1 hash algorithm in conjunction with the RSA public key algorithm. OpenSSH will disable this signature scheme by default in the near future.

Note that the deactivation of “ssh-rsa” signatures does not necessarily require cessation of use for RSA keys. In the SSH protocol, keys may be capable of signing using multiple algorithms. In particular, “ssh-rsa” keys are capable of signing using “rsa-sha2-256” (RSA/SHA256), “rsa-sha2-512” (RSA/SHA512) and “ssh-rsa” (RSA/SHA1). Only the last of these is being turned off by default.

也就是说 8.8p1 版的 openssh 的 ssh 客户端默认禁用了 ssh-rsa 算法, 但是对方服务器只支持 ssh-rsa, 当你不能自己升级远程服务器的 openssh 版本或修改配置让它使用更安全的算法时, 在本地 ssh 针对这些旧的ssh server重新启用 ssh-rsa 也是一种权宜之法.

https://ttys3.dev/post/openssh-8-8-p1-no-matching-host-key-type-found-their-offer-ssh-rsa/

key type ssh-rsa not in PubkeyAcceptedAlgorithms

Mar 29 12:58:48 roy-dev sshd[132418]: userauth_pubkey: key type ssh-rsa not in PubkeyAcceptedAlgorithms [preauth]

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vim /etc/ssh/sshd_config
PubkeyAcceptedKeyTypes +ssh-rsa

It is now possible[1] to perform chosen-prefix attacks against the SHA-1 algorithm for less than USD$50K.

OpenSSH 8.2发布禁用ssh-rsa算法

https://cloud.tencent.com/developer/article/1589118

另一方面关于 SHA-1 哈希算法，此前该算法被发现构造前缀碰撞攻击成本已降至低于 5 万美元（实际为 4.5 万美元），因此开发团队决定禁用 ssh-rsa 公钥签名算法。

有一些更好的算法可以替代，包括 RFC8332 RSA SHA-2 签名算法 rsa-sha2-256/512、ssh-ed25519 签名算法与 RFC5656 ECDSA 算法。目前这些算法在 OpenSSH 中都已经支持。

完整的更新说明查看：http://www.openssh.com/txt/release-8.2

winscp 使用 5.20.1 beta 以上的版本默认不使用 ssh-rsa 签名算法 .

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HostKeyAlgorithms
             Specifies the protocol version 2 host key algorithms that the client wants to use in order of preference.  The default for this option is:

                ecdsa-sha2-nistp256-cert-v01@openssh.com,
                ecdsa-sha2-nistp384-cert-v01@openssh.com,
                ecdsa-sha2-nistp521-cert-v01@openssh.com,
                ssh-rsa-cert-v01@openssh.com,ssh-dss-cert-v01@openssh.com,
                ssh-rsa-cert-v00@openssh.com,ssh-dss-cert-v00@openssh.com,
                ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
                ssh-rsa,ssh-dss

             If hostkeys are known for the destination host then this default is modified to prefer their algorithms.

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