title: “OpenCloudOS SSH连接执行报错” tags:

• WebShell slug: ‘2e548447’ date: 2024-06-12 23:04:12 summary: “本文是作者对OpenCloudOS SSH连接执行报错的介绍，包括OpenCloudOS SSH连接执行报错的优势、实现细节、相关资料等，这些步骤可以帮助作者提高OpenCloudOS SSH连接执行报错的效率。”

WebShell SSH login to OpenCloudOS 9 disconnects immediately. After some investigation I found the root cause — here’s a summary.

WebShell SSH login flow

WebShell uses nodejs-ssh2 to implement terminal login:

1. SSH connect opens an interactive shell for login.
2. After successful login, the underlying SSH connection is reused to open exec channels to run commands. Here, four commands were executed concurrently.

Error logs

With debug logs enabled, you’ll see something like this:

...
Inbound: CHANNEL_DATA (r:0, 57)
Inbound: CHANNEL_OPEN_CONFIRMATION (r:1, s:1)
Outbound: Sending CHANNEL_REQUEST (r:1, exec: env)
Inbound: CHANNEL_OPEN_CONFIRMATION (r:2, s:2)
Outbound: Sending CHANNEL_REQUEST (r:2, exec: curl https://1991421.cn)
Inbound: CHANNEL_OPEN_CONFIRMATION (r:3, s:3)
Outbound: Sending CHANNEL_REQUEST (r:3, exec: pwd)
Inbound: CHANNEL_OPEN_CONFIRMATION (r:4, s:4)
Outbound: Sending CHANNEL_REQUEST (r:4, exec: id)
Socket ended
Socket closed
/Users/alanhe/GitHub/express-demo/node_modules/ssh2/lib/client.js:1836
      cb(had_err !== true ? had_err : new Error('Unable to exec'));                    ^

As you can see, the connection drops directly, leading to the final error “Unable to exec”.

Analysis

1. 尝试关闭命令执行，或者只保留1个命令执行，发现是OK的。

2. The machine had 1 vCPU and 1 GB RAM. Upgrading to something like 8 GB removed the error.

3. 重装系统到OpenCloudOS 8发现即使是同配置没问题。

4. OpenCloudOS9的OpenSSH是v9.3，而8的是v8.x，测试其它镜像比如Fefora 40 OpenSSH v9.6是没问题。

Therefore, I suspect version 9 has some limit that causes the connection to drop when too many exec channels are opened. This does not appear to be a general OpenSSH 9.x compatibility issue.

Check server-side OpenSSH version

ssh -V

Fixes

1. Ideally OpenCloudOS 9 should fix this SSH issue — other systems don’t exhibit it.
2. Until the specific limit is identified, disable or avoid concurrent execs to work around it.

Final Thoughts

While I haven’t pinpointed exactly where the OS enforces this limit, the cause is clear enough. Running commands in parallel isn’t inherently wrong and shouldn’t be a problem, but don’t open too many channels — settings like MaxSessions will still cap things.