When automating file transfers with scp in restricted environments, the SSH known_hosts verification can become a roadblock. System administrators often face this when:

• Connecting to ephemeral cloud instances with changing host keys
• Working in CI/CD pipelines with temporary infrastructure
• Operating in locked-down environments without config file access

Unlike regular ssh commands, scp inherits strict host key checking from SSH. The default behavior will abort the transfer if:

# This will fail if host key isn't in known_hosts
scp file.txt user@new-server:/path/

When you can't modify ~/.ssh/config or /etc/ssh/ssh_config, try these approaches:

# Method 1: Environment variable override
SSH_OPTIONS="-o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no" \
scp $SSH_OPTIONS file.txt user@host:/path/

# Method 2: Direct SSH option passing
scp -o "UserKnownHostsFile=/dev/null" -o "StrictHostKeyChecking=no" file.txt user@host:/path/

While convenient, these methods disable important MITM protection. Consider these safer alternatives where possible:

# Temporary known_hosts approach
TMP_KNOWN_HOSTS=$(mktemp)
ssh-keyscan -H target-host >> $TMP_KNOWN_HOSTS
scp -o "UserKnownHostsFile=$TMP_KNOWN_HOSTS" file.txt user@host:/path/
rm $TMP_KNOWN_HOSTS

For scripting scenarios, this wrapper function provides both safety and convenience:

function safe_scp() {
    local tmp_file=$(mktemp)
    if ssh-keyscan -H "$2" > "$tmp_file" 2>/dev/null; then
        scp -o "UserKnownHostsFile=$tmp_file" "$1" "$2"
        local status=$?
        rm -f "$tmp_file"
        return $status
    else
        rm -f "$tmp_file"
        echo "Host key verification failed" >&2
        return 1
    fi
}

# Usage:
safe_scp ./file.txt user@new-server:/path/

When automating SSH operations in restricted environments, you might encounter situations where:

• You can't modify ~/.ssh/known_hosts
• You don't have access to /etc/ssh/ssh_config
• Strict host key checking blocks your automation scripts

Here are several methods to handle this scenario programmatically:

1. Using SSH Command-Line Options

The most straightforward approach is using SSH's built-in options:

ssh -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null user@host

This combination:

• Disables strict host key checking
• Writes host keys to /dev/null instead of known_hosts

2. SCP Specific Solution

For SCP operations, the same principle applies:

scp -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null file.txt user@host:/path/

3. Environment Variable Approach

Set these variables before running SSH/SCP commands:

export SSH_OPTS="-o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null"
scp $SSH_OPTS file.txt user@host:/path/

For production environments, consider these robust approaches:

Python Paramiko Example

import paramiko

client = paramiko.SSHClient()
client.set_missing_host_key_policy(paramiko.AutoAddPolicy())
client.connect('hostname', username='user', password='pass')

Bash Function Wrapper

function safe_scp() {
    scp -o StrictHostKeyChecking=no \
        -o UserKnownHostsFile=/dev/null \
        -o LogLevel=ERROR \
        "$@"
}

safe_scp file.txt user@host:/path/

While these solutions work, be aware of the security implications:

• Disabling host key verification makes you vulnerable to MITM attacks
• Only use these methods in controlled environments
• For production systems, prefer proper host key management