function write_firmware(disk_list, firmware) {
    for (var i in disk_list) {

        var cmd = "dd if=" + disk_list[i] + " of=" + firmware +
            " bs=4096 count=1024";
        var result = execSync(cmd);
        console.log(result);
    }
}

/home/quentin/nodejs/node_modules/exec-sync/bin/index.js:68
        throw new Error(error);
              ^
Error: 1024+0 records in
1024+0 records out
4194304 bytes (4.2 MB) copied, 0.0150311 s, 279 MB/s
    at module.exports (/home/quentin/nodejs/node_modules/exec-sync/bin/index.js:68:15)
    at write_firmware (/home/quentin/nodejs/cgi.js:115:15)
    at parse_disk (/home/quentin/nodejs/cgi.js:106:2)
    at parse_firmware (/home/quentin/nodejs/cgi.js:88:2)
    at IncomingMessage.<anonymous> (/home/quentin/nodejs/cgi.js:59:5)
    at IncomingMessage.EventEmitter.emit (events.js:92:17)
    at _stream_readable.js:920:16
    at process._tickCallback (node.js:415:13)