背景介绍
公司同事反馈测试环境某台机器ssh登录特别慢，我接到此需求后对该机器上的ssh问题进行处理并对测试环境所有机器进行依次验证ssh速度。
参考文档
解决思路
按照ssh调优的步骤检查UseDNS和GSSAPIAuthentication
如果上述方式调整后仍然很慢则开启debug模式 ssh -vvv进行后续分析
问题原因
由于设置公司机器环境数据，采用A B方式进行脱敏，代替发现问题的机器。
测试环境中A机器是由于：没有关闭UseDNS和GSSAPIAuthentication导致登录较慢
测试环境中B机器是由于：设置了ssh登录的欢迎信息，并且欢迎信息中带有机器磁盘、内存、CPU的使用信息导致ssh远程时较慢。
A机器这种情况相对容易解决，具体步骤如下
# 调整ssh的参数，并将其设置为no关闭状态
vim /etc/ssh/sshd_config
UseDNS no
GSSAPIAuthentication no
# 重新启动sshd
systemctl restart sshd
着重记录下B机器这种情况。
在对测试环境中所有机器进行验证时发现B机器登录极其慢，比A机器这种情况还要慢很多。
登录到B机器后查看UseDNS和GSSAPIAuthentication都是关闭状态的，看来问题不在于该参数。
debug过程
我做了一个对比实验，ssh -v debug时找了一台正常的机器C ，得到正常速度的debug信息，然后对比B机器debug信息，查找问题所在。
B机器debug信息
[root@server200 sync]# time ssh root@xxxx -v
OpenSSH_7.4p1, OpenSSL 1.0.2k-fips 26 Jan 2017
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 58: Applying options for *
debug1: Connecting to xxxxx [xxxxx] port 22.
debug1: Connection established.
debug1: permanently_set_uid: 0/0
debug1: identity file /root/.ssh/id_rsa type 1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_rsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_dsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_dsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_ecdsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_ecdsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_ed25519 type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_ed25519-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_7.4
debug1: Remote protocol version 2.0, remote software version OpenSSH_8.2p1 Ubuntu-4ubuntu0.11
debug1: match: OpenSSH_8.2p1 Ubuntu-4ubuntu0.11 pat OpenSSH* compat 0x04000000
debug1: Authenticating to xxxxx:22 as 'root'
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: algorithm: curve25519-sha256
debug1: kex: host key algorithm: ecdsa-sha2-nistp256
debug1: kex: server->client cipher: [email protected] MAC: <implicit> compression: none
debug1: kex: client->server cipher: [email protected] MAC: <implicit> compression: none
debug1: kex: curve25519-sha256 need=64 dh_need=64
debug1: kex: curve25519-sha256 need=64 dh_need=64
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: Server host key: ecdsa-sha2-nistp256 SHA256:7sRACE1rYEAUxbJ0HEOLwC+bz4rMzNWZmkUklQOh4hQ
debug1: Host 'xxxx' is known and matches the ECDSA host key.
debug1: Found key in /root/.ssh/known_hosts:6
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_EXT_INFO received
debug1: kex_input_ext_info: server-sig-algs=<ssh-ed25519,[email protected],ssh-rsa,rsa-sha2-256,rsa-sha2-512,ssh-dss,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,[email protected]>
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey,password
debug1: Next authentication method: publickey
debug1: Offering RSA public key: /root/.ssh/id_rsa
debug1: Server accepts key: pkalg rsa-sha2-512 blen 279
debug1: Authentication succeeded (publickey).
Authenticated to xxx ([xxx]:22).
debug1: channel 0: new [client-session]
debug1: Requesting [email protected]
debug1: Entering interactive session.
debug1: pledge: network
debug1: client_input_global_request: rtype [email protected] want_reply 0
debug1: Remote: /root/.ssh/authorized_keys:2: key options: agent-forwarding port-forwarding pty user-rc x11-forwarding
debug1: Remote: /root/.ssh/authorized_keys:2: key options: agent-forwarding port-forwarding pty user-rc x11-forwarding
debug1: Sending environment.
debug1: Sending env LANG = en_US.UTF-8
Welcome to Ubuntu 20.04.6 LTS (GNU/Linux 5.4.0-169-generic x86_64)
* Documentation: https://help.ubuntu.com
* Management: https://landscape.canonical.com
* Support: https://ubuntu.com/advantage
System information as of Tue Jan 16 16:11:22 CST 2024
System load: 2.17 Temperature: 53.0 C
Usage of /: 28.1% of 111.53GB Processes: 184
Memory usage: 7% Users logged in: 1
Swap usage: 0% IPv4 address for enp2s0: xxxx
* Strictly confined Kubernetes makes edge and IoT secure. Learn how MicroK8s
just raised the bar for easy, resilient and secure K8s cluster deployment.
https://ubuntu.com/engage/secure-kubernetes-at-the-edge
Expanded Security Maintenance for Applications is not enabled.
1 update can be applied immediately.
To see these additional updates run: apt list --upgradable
23 additional security updates can be applied with ESM Apps.
Learn more about enabling ESM Apps service at https://ubuntu.com/esm
New release '22.04.3 LTS' available.
Run 'do-release-upgrade' to upgrade to it.
Last login: Tue Jan 16 16:10:46 2024 from 192.168.0.200
C机器的debug信息
[root@server200 sync]# time ssh root@xxxxx -v
OpenSSH_7.4p1, OpenSSL 1.0.2k-fips 26 Jan 2017
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 58: Applying options for *
debug1: Connecting to xxxx [xxx] port 22.
debug1: Connection established.
debug1: permanently_set_uid: 0/0
debug1: identity file /root/.ssh/id_rsa type 1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_rsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_dsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_dsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_ecdsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_ecdsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_ed25519 type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_ed25519-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_7.4
debug1: Remote protocol version 2.0, remote software version OpenSSH_7.4
debug1: match: OpenSSH_7.4 pat OpenSSH* compat 0x04000000
debug1: Authenticating to xxxxx:22 as 'root'
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: algorithm: curve25519-sha256
debug1: kex: host key algorithm: ecdsa-sha2-nistp256
debug1: kex: server->client cipher: [email protected] MAC: <implicit> compression: none
debug1: kex: client->server cipher: [email protected] MAC: <implicit> compression: none
debug1: kex: curve25519-sha256 need=64 dh_need=64
debug1: kex: curve25519-sha256 need=64 dh_need=64
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: Server host key: ecdsa-sha2-nistp256 SHA256:o7TNN/TINsGCD1/M9j9ybACmIyTJGt1Xdfyk7RDm6ww
debug1: Host 'xxxxx' is known and matches the ECDSA host key.
debug1: Found key in /root/.ssh/known_hosts:3
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_EXT_INFO received
debug1: kex_input_ext_info: server-sig-algs=<rsa-sha2-256,rsa-sha2-512>
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey,password
debug1: Next authentication method: publickey
debug1: Offering RSA public key: /root/.ssh/id_rsa
debug1: Server accepts key: pkalg rsa-sha2-512 blen 279
debug1: Authentication succeeded (publickey).
Authenticated to xxxx ([xxxxx]:22).
debug1: channel 0: new [client-session]
debug1: Requesting [email protected]
debug1: Entering interactive session.
debug1: pledge: network
debug1: client_input_global_request: rtype [email protected] want_reply 0
debug1: Sending environment.
debug1: Sending env LANG = en_US.UTF-8
Last login: Tue Jan 16 16:09:43 2024 from 192.168.0.180
debug信息的差异
B机器的debug信息比正常机器的debug信息多出如下字段
debug1: Remote: /root/.ssh/authorized_keys:2: key options: agent-forwarding port-forwarding pty user-rc x11-forwarding
debug1: Remote: /root/.ssh/authorized_keys:2: key options: agent-forwarding port-forwarding pty user-rc x11-forwarding
Welcome to Ubuntu 20.04.6 LTS (GNU/Linux 5.4.0-169-generic x86_64)
* Documentation: https://help.ubuntu.com
* Management: https://landscape.canonical.com
* Support: https://ubuntu.com/advantage
System information as of Tue Jan 16 16:11:22 CST 2024
System load: 2.17 Temperature: 53.0 C
Usage of /: 28.1% of 111.53GB Processes: 184
Memory usage: 7% Users logged in: 1
Swap usage: 0% IPv4 address for enp2s0: xxxxx
* Strictly confined Kubernetes makes edge and IoT secure. Learn how MicroK8s
just raised the bar for easy, resilient and secure K8s cluster deployment.
https://ubuntu.com/engage/secure-kubernetes-at-the-edge
Expanded Security Maintenance for Applications is not enabled.
1 update can be applied immediately.
To see these additional updates run: apt list --upgradable
23 additional security updates can be applied with ESM Apps.
Learn more about enabling ESM Apps service at https://ubuntu.com/esm
New release '22.04.3 LTS' available.
Run 'do-release-upgrade' to upgrade to it.
上述信息是在ssh设置的欢迎登录信息，我猜测是因为欢迎登录信息中带有大量需要统计的信息导致变慢的，该信息如下：
System load: 2.17 Temperature: 53.0 C
Usage of /: 28.1% of 111.53GB Processes: 184
Memory usage: 7% Users logged in: 1
Swap usage: 0% IPv4 address for enp2s0: xxxxx
那么关闭ssh的欢迎信息就好了，具体关闭步骤如下
具体步骤
将生成欢迎信息的脚本放到一个bak文件中即可。
root@server206:~# cd /etc/update-motd.d/
root@server206:/etc/update-motd.d# mkdir bak
root@server206:/etc/update-motd.d# mv ./* bak
root@server206:/etc/update-motd.d# ls
bak
设置完毕后重启ssh systemctl restart sshd再次登录验证已经和正常速度一样了。