执行ssh user@ip 'command'时遇can't get tty settings错误求助

I’ve run into this exact issue with Cisco IOS-based devices before—their CLI is picky about having a proper terminal environment to execute commands, which is why you see this error when running commands directly via ssh user@ip 'command' but not when logging in interactively. Here’s how to fix it:

1. Quick Fix for Manual/One-off Commands #

When running commands from your shell, force SSH to allocate a pseudo-terminal with the -t flag. This tricks the Cisco AP into thinking you’re logging in interactively:

ssh -t user@ap_ip 'your_command_here'

For example, to pull a snippet of the running config focused on interfaces:

ssh -t admin@192.168.1.1 'show running-config | include interface'

The -t flag ensures the AP gets the tty settings it expects, eliminating the "can't get tty settings" error entirely.

2. Fixing Your Golang Automation #

The Go x/crypto/ssh library doesn’t request a pseudo-terminal by default, which is why your automation is hitting the same roadblock. You need to explicitly request a PTY in your session setup. Here’s a working example:

package main

import (
    "fmt"
    "golang.org/x/crypto/ssh"
    "os"
)

func main() {
    // Configure SSH client credentials
    config := &ssh.ClientConfig{
        User: "admin",
        Auth: []ssh.AuthMethod{
            ssh.Password("your_secure_password"),
        },
        // Note: In production, replace this with proper host key verification!
        HostKeyCallback: ssh.InsecureIgnoreHostKey(),
    }

    // Connect to the AP
    client, err := ssh.Dial("tcp", "192.168.1.1:22", config)
    if err != nil {
        fmt.Printf("Failed to connect to AP: %v\n", err)
        os.Exit(1)
    }
    defer client.Close()

    // Create a new SSH session
    session, err := client.NewSession()
    if err != nil {
        fmt.Printf("Failed to create session: %v\n", err)
        os.Exit(1)
    }
    defer session.Close()

    // Critical step: Request a pseudo-terminal (PTY)
    err = session.RequestPty("vt100", 80, 40, ssh.TerminalModes{})
    if err != nil {
        fmt.Printf("Failed to request PTY: %v\n", err)
        os.Exit(1)
    }

    // Execute your command and capture output
    output, err := session.CombinedOutput("show version")
    if err != nil {
        fmt.Printf("Command execution failed: %v\n", err)
        os.Exit(1)
    }

    // Print the result
    fmt.Println("Command Output:\n", string(output))
}

The RequestPty method mimics the interactive terminal environment the Cisco AP expects, resolving the tty-related errors. Adjust the terminal type (vt100) and dimensions (80x40) if needed—most Cisco devices work perfectly with these defaults.

Why This Happens #

Cisco 2800 APs (and many IOS-based devices) rely on terminal settings to handle command execution properly. When you run commands directly via ssh user@ip 'command', SSH doesn’t allocate a pseudo-terminal by default. The AP’s CLI detects this missing tty environment and throws the "can't get tty settings/can't set orig mode" error. Interactive logins automatically get a tty assigned, which is why they work without issues.

内容的提问来源于stack exchange，提问作者mwalto7