USB SSH System Backup

This file contains the full working USB SSH system configuration.

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USB SSH Script

File: /home/student/.local/bin/usb-ssh.sh

#!/bin/bash

USB_KEY=$(for d in /media/$USER/*; do
    [ -f "$d/id_rsa" ] && echo "$d/id_rsa" && break
done)

LOCAL_KEY="$HOME/.ssh/id_rsa_usb"
mkdir -p "$HOME/.ssh"

# IMPORTANT: use existing session agent only
export SSH_AUTH_SOCK=/run/user/$(id -u)/keyring/ssh

if [ -n "$USB_KEY" ]; then
    cp "$USB_KEY" "$LOCAL_KEY"
    chmod 600 "$LOCAL_KEY"
    ssh-add "$LOCAL_KEY" 2>/dev/null || true
else
    ssh-add -d "$LOCAL_KEY" 2>/dev/null || true
fi

exit 0

Systemd Service

File: /home/student/.config/systemd/user/usb-ssh.service

[Unit]
Description=USB SSH Key Handler

[Service]
Type=oneshot
ExecStart=/home/student/.local/bin/usb-ssh.sh

Systemd Path Unit

File: /home/student/.config/systemd/user/usb-ssh.path

[Unit]
Description=Watch USB mount for SSH key

[Path]
PathChanged=/media/%u

[Install]
WantedBy=default.target

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Notes

• Uses systemd user services
• Works with USB mounted under /media/$USER
• Requires SSH agent session
• Event-driven (no polling loops)