Linux send command to modem

Linux send command to modem. Or when you give the hangup command yourself or leave minicom without hangup while online. In this computer there are 2 devices available: a internal 3G modem (ttyUSB0) and a external 3G dongle (ttyUSB3). Mar 27, 2024 · Our system recognizes the modem in its appropriate mode. The best way to send AT commands to a modem in Linux is to use the program atinout which is written with the sole purpose of sending AT commands to a modem from the command line. Therefore it's possible to send at-commands to it using minicom. 000000] console [tty0] enabled [ 463. Jan 20, 2016 · To switch the modem from data mode to command mode, the computer can send the special escape sequence “+++<pause>” over line A to the modem (three plaintext plus signs, followed by a pause of around one second). Jan 9, 2015 · My USB modem works fine with that echo command. The next two digits (91 in the example) refers to the country code (91-India). Commands are grouped in command lines. The modem can be forced into command mode with the #+++: Escape Sequence. This is not a standard AT command, so each manufacturer slightly differs. Jun 27, 2023 · A simple way to test modem connectivity is to send a ping through the modem. Well I thought the command 'cat device &' works. 4 Debian package offered there for installation is the latest dev branch version . See full list on thegeekstuff. If your carrier requires a different configuration, modify the AT commands accordingly. You also need to add the 2 indicators !! to connect stdin and stdout of the command to the tty. How-to guide: How can we control, configure and establish a simple data connection for a cellular module in Linux systems using the open source ModemManager tool for modem control and connection management. This option allows for that. With this option you can enable that stupidity. Second, I haven't used the full prompt, but only Jan 29, 2012 · Then right-click to open Properties of the USB Modem device and navigate to the "Diagnostics" tab. 3. We can use the built-in AT commands that control the cellular modem to send these messages. 0. Mar 18, 2024 · In Linux, it’s possible to send Short Message Service (SMS) either directly from the terminal using SMS gateways or by employing tools that support sending SMS through the command line. This list of Linux networking commands will help you work with network connections. 368192] usb 1-2 : GSM modem [1-port] converter now attached to ttyUSB1 Resets the modem to its original factory default settings. Learn how to send SMS messages from the command-line of a computer running Ubuntu Linux using an USB GSM modem. May 21, 2024 · Linux Networking Commands Cheat Sheet. Jan 20, 2022 · We're gonna talk old school AT commands to the modem, the first one being the command to check the current usbmode: AT+QCFG="usbnet" That will likely return +QCFG: "usbnet",0, but we need that to be set to 1 (ECM mode), so enter the following command: AT+QCFG="usbnet",1. If this is set to 'ALT' or 'meta key', you can directly call commands by alt-key instead of HotKey-key. This post describes how to write simple programs to use an off the shelf modem, that can be purchased for less than $10, and using a SIM card that provides Unlimited text messaging to send and receive SMS messages. In this tutorial, we’ll learn how to send SMS using the command-line interface Nov 1, 2020 · Let’s take a look at a quick example of how to use the modem’s built-in MQTT support to send data to AWS IoT Core. Sending and receiving with the xmodem command are complementary operations. In turn, to switch the modem from command mode back to data mode, the computer can send the AT command “O” to the modem. cat /dev/ttyS0. This approach is common for automation, notifications, or system monitoring. "Main. The 'log' command in the scripts is not affected by logging options Aug 23, 2018 · I want to send SMS ideally using PHP in a Linux Environment. After verifying the modem is listening, the command AT+CFUN=1 can be used to enable its full functionality. The following command checks some text files and sends only the . as follows: echo -e "\x7E\x03\xD0\xAF und normaler Text" > /dev/ttyS0. in the other terminal, you can send arbitrary hex characters and text to the terminal e. sudo minicom modem1 it seems to work. Maybe give it 30 seconds. " I've sent it the files via HyperTerminal and a proprietary program successfully, but I need to be able to do it on the Linux command line. Some Mar 29, 2019 · Since you're talking with a modem, the general way to talk with the modem is to use ModemManager, an application that handles the communication with the modem for you. But the dialer i use locks the /dev/ttyUSB0 port, which is the command port to send AT commands for my modem. Personally, I find it easiest to use cu to set up the serial connection, run whatever is needed on the remote end to start receiving data with *MODEM, and then use cu's escape codes to run sx locally. We’ve broken this up into instructions for Linux users, Mac users, and Windows users. AT Commands are instructions that provide communication and control between any cellular modem and a host controller. Sep 24, 2009 · Hello, Im trying hard to configure a SMS MODEM the GM862 This is a simpel modem with a mobile card connected to my ttyS0 i can put the command manualy in with minicom and this works. Query signal strength, AT+CSQ). Thus the smart modem is dumbed-down until it resembles a dumb modem. ) Starting from your screen session connection to the modem: Send AT; Switch into text SMS mode (easier than the other mode) by sending AT+CMGF=1 Dec 1, 2012 · I know that the USB 3G modems connects to computer by not one serial ports, one of it for diagnostics and for send AT commands and receive answers. I don't want an extra terminal. I type some crap, I get an ERROR. You can find the information in the AT command manual of your cellular module. Click on the "Query Modem" to send some test AT commands to your modem. Cellular modems can be controlled using special AT commands provided by the module manufacturer. When I do. Here is the new version with the fix. Jun 6, 2019 · Having just one channel for both data and modem commands can be inconvenient: it makes it very tricky to send any commands to the modem (e. The following configurations are based on TELUS as the current carrier. I want to use USSD command to catch the balance of the current 3G internet connection But for now the only solution that I have is to: 1- stop the wvdial (and ppp0) command in order to free the /dev/ttyACM0 device and then Nov 17, 2010 · for sim900 AT+CCID gives CCID. Use the xmodem command on the remote system in combination with the send subcommand or the receive subcommand from the ATE Connected Main Menu on the local system. AT commands ("AT" meaning 'attention') are instructions used to control a modem. Feb 19, 2018 · Found the commands that were lacking on my script. So is there any way, to send the Sep 15, 2023 · To send the data with carriage return ("\n") and the Ctrl+Z command, you can use the echo command and then pipe the output to socat. Send an AT COMMAND to the given modem. Using AT commands you can easily send an SMS message from your device. If you need to transfer a file using the xmodem protocol from the command line, you can use the sx or sb commands from the lrzsz package. init specifies AT commands needed for your modem. Balance. When initiating an USSD session, a RESPONSE may be needed by a network-originated request. The version 0. This guide will show you how to send AT commands to a Hologram Nova, but the basics apply to any device that has a modem that one can access via serial communications. I tried to do it as: sudo socat - /dev/ttyACM0 but when typing anything I just get a line repeating this command (I expect an OK). It follows praetorian droid's answer. Sep 25, 2012 · You can connect to your modem with: $ cu -l ttyACM0 (with: ttyACM0 being the device /dev/ttyACM0) You should get a response: connected At this point you can use any of the standard AT commands such as to test dialing: ATDT 123-456-7890 You should have your userid set to the group dialout for permission to access the modem. This video shows how to configure Huawei USB modem to send and receive SMS on Linux or Ubuntu machine. You can use minicom , screen or miniterm for Linux/MacOS or PuTTY for Windows. Which has some support for GSM cell phones. There are higher serial port speeds than 115200 bps, and a USB-based serial port emulation might well report them. Add support for serial interfaces (ttyUSBx) - install kmod-usb-serial-option or kmod-usb-serial-qualcomm depending on the modem. Jun 6, 2019 · The Problem. Well armia if you want a script I suggest using python along with pyserial + python-messaging-pmarti. The AT command in the second atinout command is You can use the Linux command line tool gsm-ussd to send USSD Jul 15, 2015 · The Linux command line tool gsm-ussd has support for USSD sessions that will allow you to answer to USSD menus. Configure modem with AT commands. Code would run in a look and execute various commands, and one of them would be to check if message arrived and then act upon that. mmcli -m ”). One system must be set to send while the other is set to receive. I can connect to the modem with minicom and also miniterm. Actually it depends on which modem we are using. BusyBox v1. Nov 6, 2019 · The most basic method of controlling a modem is by sending commands through a serial port. How to switch mass storage mode to modem mode, Huawei Sep 8, 2011 · A saner approach would be to delegate SMS management to a specialized software, because in my experience there's more to do to manage SMS sends than just throwing a couple of bytes to a modem network availability checks and the corresponding retries to optimize your delivery rate Aug 28, 2013 · I want to send SMSs in PDU mode. com Nov 12, 2016 · The output above is assuming ATE1; without echo the response from the modem will be "\r\n\r\nOK\r\n\r\nOK\r\n". There are several serial monitor tools that can be used to send AT commands to the cellular module. A terminal program like picocom will be needed to actually send AT commands. Leveltrim?" should Read the Balance Level trim and return it back via the serial port. – This option defines whether or not the logfile is written when the remote end answers the call or hangs up. I'm setting up a script in python to communicate with my USB GSM Modem through AT commands. This allows you to fire up a terminal and interact with the modem directly by issuing AT commands of your own. −−3gpp−ussd−respond=RESPONSE. txt and . Here is the sequence of commands, with some comments on the right that obviously don't have to be included Apr 5, 2022 · Turning on the Modem. The CODE provided is vendor specific. For detailed installation and configuration instructions see here . Another possibility for such disconnections is to help the customer save bandwidth, which might be expensive. Jan 29, 2024 · −−3gpp−ussd−initiate=COMMAND. Without the correct vendor code, it's unlikely this operation will succeed. However, this didn't work for me until I also used the cat command (cat < /dev/ttyS0) while I was sending the echo command Fix (it works on ZTE-mf190 at least) is simple - send this command through serial port (use minicom or similar soft): AT+ZCDRUN=E\r\n This command will delete a NODOWNLOAD. I type an AT and get an OK. But the problem is that they need a terminal to send/receive AT commands to the modem. May 4, 2021 · +++ (send + character, wait for 700ms, send + character, wait for 700ms, send + character) => back to AT command mode ATO (back to data mode) NOTE: the APN your provider expects, is I think in all cases an easy Google. as follows: Nov 24, 2020 · so that every answer from the modem is automatically redirected to your console. This post explains how to install and use these commands, and provides some examples and tips. But it doesn't. minicom everything works as expected. Actually, i'm not sure that i have to send commands to this file, but others don't reply too. I have checked the spec for my modem, and it supports PDU mode. Provided by: modem-cmd_0. I have a udev script that runs this for every ttyS and ttyUSB device. for monitoring radio signal strength) while the network connection is active. Aug 3, 2024 · With the SIM card and modem installed in the USB adaptor, plug the modem into a USB port and wait. May 1, 2016 · This assumes that your modem is at /dev/ttyUSB1. Oct 16, 2015 · Okay, so warnings aside, how exactly do we send an SMS? Well, as with any other modem command, we use an AT command that’s defined by the GSM Standard, in this case “AT+CMGS”. Once the ppp connection is active, i would like to send some AT commands(for ex. I can easily enough call AT+CFUN:1 through the minicom application console to enable radio again. When finished use the Quit option to leave Minicom without sending a reset string to the modem; this option is Alt-Q. The first two digits (89 in the example) refers to the Telecom Id. B - Backspace key sends There still are some systems that want a VT100 to send DEL instead of BS. Jun 19, 2016 · Looks like i should send commands to /dev/ttyGS0, but it doesn't reply. -k, --1k (XMODEM/YMODEM) Send files using 1024 byte blocks rather than the default 128 byte blocks. At this point, if a modem is capable of In Linux (Ubuntu) I am trying to send AT commands to a modem at /dev/ttyACM0. Aug 26, 2016 · @FiddlingBits Just to the modem, I'm just stuck trying to send multiple "AT" commands, but if you know of another way to send a script that I can do using system() calls, that would be a much simpler solution. Below you can also see a brief description and the response of each AT command. That is OK for any command I need to send the amplifier. Linux is used to power everything from simple desktop faxing to enterprise level fax servers with many lines and users. Nov 16, 2013 · On a real Linux computer the device gets detected as a storage device and modem as well (ttyUSB0). When sending files from a Macintosh system to a Unix or Linux host via Zmodem protocol, remember that the filenames cannot have spaces in them. 01 Sep 14, 2018 · You do this by sending an exec command to the screen process, followed by the sz command to execute. How do I go about doing this? I went through a lot of articles but they were more about setting up the modem rather than using it in this particular way. System Requirements. cat /dev/ttyS0 in the other terminal, you can send arbitrary hex characters and text to the terminal e. Mar 25, 2015 · I would like to process sms messages from my GSM modem (SIM900, but have few others also) but without +CMTI notification. 367652] usb 1-2 : GSM modem [1-port] converter now attached to ttyUSB0 [ 463. I disabled the CD-drive (storage device) with the the computer executing this command: AT^U2DIAG=0. After executing these commands, NetworkManager will automatically try to bring up the cellular connection whenever ModemManager reports that the modem has registered (the state of the modem can be checked with the previously introduced command “sudo modem-manager. Mar 27, 2012 · When I send an AT command to the modem with SCREEN (plugged into the embedded controller board running Linux) it responds with the correct responses. py. The command set consists of a series of short text strings that can be combined to produce commands for operations such as dialing, managing SMS functions, and changing the parameters of the connection. And specifically for AT+CMGS you MUST wait for the modem to send "\n\r> " before you should start sending MyMessage. 13. Aug 19, 2021 · A perpetually connected device that uses a data plan can become prohibitively expensive if you want to just send short messages. Apr 23, 2015 · device is where you specify the file descriptor for your modem. Modem used is Try to specify the call index from the last command output (seem 1 in your Apr 10, 2013 · I need to send AT command to modem. Some examples: SIMCom SIM7020 uses AT+CIPPING: SIM7020 Series_AT Command Manual_V1. Examples: To configure a modem use the command minicom -o console to start Minicom without sending an initialization string to the modem. And you need to send the usual control-a: prefix and colon to make screen take your input as a command. Can anybody please tell me an easy way to send SMS from Linux using a USB GSM modem? Apr 4, 2020 · The modem has connection to the Internet an can receive and send SMS. Now use the minicom command from earlier to verify that you can talk to the modem and the SIM card is connected: at!entercnd="A710" at+cpin? It should respond with "READY". I would like to send my usb modem texts from my cell phone and would want my usb modem to store it in some log file and may be communicate back. Now issue the AT commands to configure the modem. Aug 28, 2012 · in the BusyBox command for Linux exists the command microcom to communicate with a serial modem:. In order to send AT Commands, you need to connect to the modem first. Most modems today are smart modems based upon the Hayes modems and their command sets. For full description of AT commands, see Quectel_BG96_AT_Commands_Manual [13]. I've read article on XDA-developers, but it didn't help. Installation of these In the field, a cellular-enabled IoT device will manage its modem by sending it AT commands, but during application development and debugging, it's not uncommon to tap the modem's USB connection. “SMS Modes” When sending/receiving SMS on a GSM Modem, you can use either PDU mode or Plain Mar 28, 2012 · I take it that you are talking to a linux (BASH) like shell ie. You may need a program which provides the interface between your computer and the modem. 3. The modem responds and outputs the results (on stdout). Mar 22, 2024 · To send AT commands to a LTE modem, you need to first connect the device/modem to the computer, most likely using an adapter (built-in modem slots are very rare these days) and access it with a COM terminal. How can I send AT Commands to a cellular module? Jan 18, 2022 · For this purpose, we introduced a Python program template that allows users to submit a sequence of AT control commands to the sixfab LTE-M/NB-IoT modem which is based on a Quectel BG96 network interface module. I am using samsung galaxy S3 I9300 device, which is rooted. It taked a while for the modem to boot up. In this case, the character > doesn't mean you can directly send the text; you'll have to go on sending it with echo -e. Currently if modem received sms it outpus +CMTI message which get somewhere in the buffer. C - Log file transfers Do you want log entries of receiving and sending files. For example, COMMAND could be 'AT+GMM' to probe for phone model information. I was missing the "AT+VTX" command before sending the audio data. If you’re using a USB modem, this will almost allways be /dev/ttyUSB0. g. This is not a common user action. You can use it to test if a modem is up and running, make a backup of the phone book: $ atinout - /dev/ttyACM0 ten_first_phonebook_entries. The Nokia phones use other device names, like ttyACM0. All you have to do is open two terminals. Plus, you don't have to type echo and quotes every time. Request the given modem to initiate a USSD session with COMMAND. This Aug 20, 2017 · I want to write a simple code in python to send USSD codes to a GSM modem (D-link DWM-157) and receive their results and store them in variables. Jun 28, 2013 · OK so only screen is able to send the commands to the Serial port. May 12, 2016 · Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand Apr 1, 1997 · First, the modem initialization string I've suggested will, in most modems, ensure that the modem will raise the Data Carrier Detect line when a call is connected, and will hang up the call if the DTR line is lowered. However, since it provides a DBus API, it is possible to use 'dbus-send' commands or the new 'mmcli' command line interface to control it from the terminal. This means it can be used as a phone dialer. Jan 30, 2008 · create a modem config file by entering minicom -s from the root command line select the options you want to configure using AT commands connect to the modem by typing in minicom ↩ ∞ AC Nov 10, 2011 @ 12:28 Oct 12, 2012 · In Android you talk to the rild (Radio Interface Layer) daemon, which in turns talks to a proprietary library, which sends commands to the actual hardware. Use the following command to establish a TCP connection to the LAN modem and send your serial data: echo -e "YourSerialDataHere\n\x1A" | socat - TCP4:172. I've tried the following commands: echo "AT\r" > /dev/ttyGS0 echo "ATD12345678900;\r" > /dev/ttyGS0 but nothing happens. But as discussed above, the Linux serial console is designed to operate with a dumb modem. You will notice that the AT commands are specific to the Onyx modem, which is evidenced by the fact the commands start with ‘AT+Q’. Send COMMAND to the receiver for execution, return immediately upon the receiving program's successful recption of the command. When trying to send AT commands in ModemManager I get the following error:"Cannot send AT command to modem: operation only allowed in debug mode" Jul 29, 2015 · Sending SMS. If this doesn't work, you have a problem, and I don't have an answer. Now i want to automate this function to send is out in a script The commands that needed to be send to the modem are : ATZ0 AT+CSCA? Screen and keyboard A - Command key is the 'Hot Key' that brings you into command mode. Now i want to build a little script that automatically send AT command to modem plugged on iMX53. OK) and first then continue processing the next command. The device still won't get detected as a modem. OK, ERROR, ) before sending the next command. . Before I show you this, however, you need to know one more thing. SCREEN is a program like Minicom (on linux) or HyperTerminal (on windows). In your code, you first issue the "echo" command, which indeed sends the string "AT" to your modem device. doc files that exist on both systems and that are newer on the sending system. If you are not familiar with using COM terminals, you might want to use a graphical tool like: CuteCom or minicom. You could probably write a command line program that talks to the rild and execute it via adb shell, if that fits your needs. Dec 29, 2018 · Every time my USB modem (/dev/dlinkModem) gets unplugged it defaults to "radio disabled mode" (AT+CFUN:4). That is needed to interact with the modem using AT commands, for configuration purposes or to be able to send/receive SMS and USSD. After connecting to your modem’s serial port, you can verify your modem is listening by sending ATI, which will return some basic information about the modem and its status. Jul 8, 2024 · 2. You can use these commands to set up the networks, fix connection problems, and see the information about the network. 16. To send (or receive) a fax from a Linux Computer using Fax software you’ll need the following: Jan 29, 2010 · No, no, no! Please do not process AT commands in this way. The result should look something like this: Is there a way to autodetect modem devices in Linux and then symlink them to /dev/modem using a udev rule? Currently, I wrote a program that probes each serial port, sending AT and waiting for OK. 12. The extra devices created are useful to get and query the internal modem state while the main one is in use (you may try the cat command on them). This ensures that the modem is matched with the modem option supplied to pppd. Replace "YourSerialDataHere" with the Feb 17, 2024 · AT commands are accepted by the modem only when in command mode. You need to redirect the output for it to do anything useful. I open the device in perl like this (I do not have Device::Serialport on my embedded Linux perl installation): Feb 7, 2020 · @RobertoCarboni yes, I'm able to modify the code and send new AT commands to the modem but i dont want to set an hardcoded apn since it should works with any possible SIM card used. (Note that SMS may incur additional charges. So to test the communication is working correctly I first try to send a simple AT expecting to receive an OK, but instead with every read request I still receive only empty strings. FLG file in the modem's filesystem - it will disable such checks. 2 (2012-05-10 17:13:08 CEST) multi-call binary Usage: microcom [-d DELAY] [-t TIMEOUT] [-s SPEED] [-X] TTY Copy bytes for stdin to TTY and from TTY to stdout Options: -d Wait up to DELAY ms for TTY output before sending every next byte to it -t Exit if both stdin and TTY are silent The device has a command which tells it to anticipate a file transfer; I believe this takes the place of rz, but the device documentation says it "Prepares the device for YMODEM transfer via HyperTerminal. I have a GSM modem which I want to use to send SMS. – Aug 9, 2021 · There are a number of options in the open source community when it comes to fax software on a linux computer. Nearly all dial-up modems support Hayes AT commands, such as ATD or ATH (usually in hardware for serial modems, sometimes emulated by the driver for USB/PCI modems). Try: stty -echo to prevent the port from echoing the commands back to the modem. For more information on specific AT Commands check out this guide: Introduction to AT -i COMMAND, --immediate-command COMMAND Send COMMAND to the receiver for execution, return immediately upon the receiving program's successful reception of the command. May 13, 2015 · I have a zte 3g modem. This leads me to think it might be some kind of perl buffering issue, but that's only guessing. These commands have been tested on hyperterminal and work fine, but when sendind them through the modem I get, first, and "OK" for the first "AT" command, which is good, but then, upon sending the next command, the modem answers with "AT+CC"which I have no idea what it means. The only exception is the #A/: Repeat Last Command command. I looking for library for C/++ under linux which universal supports many USB 3G modems and give me possibilities to send AT-commands to modem while it connected via pppd. If you are unable to use ModemManager or you must use bash for some reason, note that commands must end with a \r\n to be used by the modem. 2_amd64 NAME modem-cmd - send arbitrary AT commands to your modem SYNOPSIS modem-cmd [ device ] [ command ] DESCRIPTION This manual page documents briefly the modem-cmd commands. I realize Screen isn't the "Linux command line" as the post specifically asks for, but I think it's in the same spirit. For example, COMMAND could be ’*101#’ to give your current pre-pay balance. Oct 29, 2015 · sx doesn't talk to serial ports by itself; it communicates over stdout. 1024 byte packets speed file transfers at high bit rates. 100:10001. However the amplifier is also able to send me back the status if I send it certain commands. Let’s read the device file of our modem using the dmesg command tool: $ dmesg | grep ttyU* [ 0. I use carrier provided dialer for connection establishment. I have developed a PDU encoder and decoder, but now I do not know how to send data to my modem. In the example above, atinout will send the first command AT (properly terminating the command line with \r), wait until it receives a Final Result Code (e. The steps I did are: abd shell su echo -e "AT\r" But I am not sure how to read the response given by the above commands. Check rild source code for details. “SMS Modes” When sending/receiving SMS on a GSM Modem, you can use either PDU mode or Plain Apr 10, 2013 · I need to send AT command to modem. --command=COMMAND. The devices are queried from udev and automatically updated based on hardware events, although a manual re-scan can also be requested to look for RS232 modems. Jan 25, 2006 · If that doesn't work, try putting it in a subshell, so by enclosing the command in regular braces ie (). you can use commands such as ls, etc Are you sending the commands to the modem using a construct similar to the following ? echo "ati" > /dev/ttyUSB3 or echo "ati > /dev/modem If you are and that works then you can redirect and append the output of echo to file to build a file of May 26, 2014 · Re: Port "busy" when trying to send AT commands to modem Wed Dec 19, 2018 6:58 pm There is a commandline tool called "lsof" which lists all open files and which programs that uses them. In the first terminal you cat everything from the device, e. Nov 22, 2013 · If I send the ATZ command manually with e. Each command line must start with the #AT: Command Prefix and terminated with #<CR>: End-of-line Character. e. You MUST wait for the final result code (e. txt <<EOF. Aug 1, 2024 · Summary. If you are an experienced network admin or just starting to learn the Linux networking commands this Apr 11, 2023 · I am running wvdial (ppp0) on a modem (/dev/ttyACM0) Mobile broadband on linux to supply internet to a small group of users. Some collegues of mine said that it should be automatic but when I use the AT+CGDCONT? command it returns the apn previously hardcoded into the code (there were a Mar 1, 2018 · So I have this program in C, that sends AT commands to a modem. 7. modem-cmd can be used to send arbitrary AT commands to a modem device over a serial line. 89912200000280775659. I tried these AT commands: AT AT+CMGF=0 after sending these commands I sent the PDU data like this: Mar 27, 2015 · I am using a huawei e355 usb modem on linux. echo. Looks like the modem is echoing the command back to you (expected) but then the tty port is sending the command back to the modem and creating your endless loop. lffql zpov ekumxp awsiop quetr gorxdh opn fohug boz lnensvjku