SSH Connection with Remote Linux devices

Vijaykarthikeyan

I have a shell script which should be run in rasberry pi which is a linux OS based system. I have tested in command prompt to ensure the file should be openable.

Microsoft Windows [Version 10.0.19045.3803]
(c) Microsoft Corporation. All rights reserved.

C:\Users\hp>ssh votpl@192.168.56.1
username@host
 password:
Linux pi 6.1.21+ #1642 Mon Apr  3 17:19:14 BST 2023 armv6l

The programs included with the Debian GNU/Linux system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.

Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.
Last login: Sat Jan  6 21:49:32 2024 from 192.168.56.100

Wi-Fi is currently blocked by rfkill.
Use raspi-config to set the country before use.

username@pi:~ $ cd Desktop
username@pi:~/Desktop $ ./ROV.sh
python: no process found
No Arduino
connection reset
No Arduino

This is the command prompt response for the ssh connection.Now , the file is opening via command prompt.Now,I want to automate this process..So,that on running a script in Qt..I should connect via ssh automatically at the backend. Screenshot 2024-01-19 145826.png

How to script this process.I have used QProcess but it throws error like this:
SSH Error: "Process failed to start: The system cannot find the file specified.

// SshHandler.cpp
#include "SshHandler.h"
#include "qdebug.h"

SshHandler::SshHandler(QObject *parent)
    : QObject(parent)
    , sshProcess(new QProcess(this))
{
}

void SshHandler::connectToRemoteDevice(const QString &host,
                                       const QString &username,
                                       const QString &password)
{
    // Assemble the SSH command
    QStringList sshArgs;

    sshArgs << "-T"
            << "ssh" << username + "@" + host << password << "cd Desktop && ./ROV.sh";

    // Start the SSH process
    sshProcess->start("ssh", sshArgs);

    qDebug() << "SSH Error: " << sshProcess->errorString();

}

jsulm

@Vijaykarthikeyan said in SSH Connection with Remote Linux devices:

SSH Error: "Process failed to start: The system cannot find the file specified

Well, make sure the ssh executable can be found. For example you can use absolute path to ssh.exe

Also, you should not call errorString right after starting the process because start() is asynchronous. Better connect a slot to the error signal.

Christian Ehrlicher

And why is sh needed here at all? Start ssh directly.

Vijaykarthikeyan

@Christian-Ehrlicher ok edited..But,even though im running it shows, SSH Error: "Unknown error".

I don't know the correct command line arguments..can someone guide me please

Vijaykarthikeyan

@jsulm like this?

    connect(sshProcess,
            &QProcess::readyReadStandardOutput,
            this,
            &SshHandler::onSshReadyReadStandardOutput);
    connect(sshProcess,
            &QProcess::readyReadStandardError,
            this,
            &SshHandler::onSshReadyReadStandardError);

Christian Ehrlicher

I doubt the password can be passed on the command line. Take a look on how to pass a password to ssh but for sure it's not as a simple argument.

jsulm

@Vijaykarthikeyan said in SSH Connection with Remote Linux devices:

like this?

Did you see https://doc.qt.io/qt-6/qprocess.html#errorOccurred ?

Vijaykarthikeyan

@Christian-Ehrlicher yes..i thought that too.when i gone through examples,they have said sshpass for automating the authentication.But,I need to know that is that only problem..I dont know how the QProcess take the arguments..Im doubtful about the argument list. Although classes like TCP socket and sslsocket used to networking,but i dont know whether they could access passwords too.In Qt kits..There is an option for ssh feature but don't know that very well

Christian Ehrlicher

@Vijaykarthikeyan said in SSH Connection with Remote Linux devices:

I dont know how the QProcess take the arguments..I

I don't see what this has to do with the password problem - you provide wrong arguments to ssh, ssh bails out with Unknown error - everything else would be surprising. Also ssh for sure does not simply take an argument cd Desktop && ./ROV.sh which is executed after the login.
You first have to inform you about the correct ssh parameters for your task. No Qt problem here.

Vijaykarthikeyan

@Christian-Ehrlicher Yes of course..that's what i have said that i have doubtful about the arguments..i dont know how to give the arguments likewise in command line. There is no Qt documentation for this.

Vijaykarthikeyan

@Christian-Ehrlicher So even before im trying to read the file in the remote directory,i want to ensure that whether it is connected or not by just giving hostname and username but im receiving this:

SSH Error: "ssh: connect to host port 22: Connection refused\r\n"

jsulm

@Vijaykarthikeyan You should not use passwords but identity files, then there is no need to provide password.

"ssh: connect to host port 22: Connection refused" - this means that there is no SSH server listening on port 22 on that machine, again nothing Qt specific.

Vijaykarthikeyan

@jsulm are the key files to be located on both client and server sides? or from development side?in Qt tools,there is an option for ssh connection
Screenshot 2024-01-19 164812.png

can i refer this.
https://doc.qt.io/qtcreator/creator-developing-generic-linux.html

(or)
can we use sshpass which is helpful for scripting?

jsulm

@Vijaykarthikeyan said in SSH Connection with Remote Linux devices:

can i refer this.

What you're doing is not related to QtCreator.
Not QtCreator is accessing the device via SSH but your application using QProcess and ssh executable. You need to generate a key file and upload it to your device, see for example https://askubuntu.com/questions/46930/how-can-i-set-up-password-less-ssh-login

Vijaykarthikeyan

@jsulm ok..thank you ..working..I have successfully run the remote linux device via command line terminal

Vijaykarthikeyan

@jsulm Now,I have the key and i tested in command terminal and it works well. Now,i don't know the command line arguments for linux to be used in QProcess. when goes through the documentation,it says the start function takes command line arguments but not mentioned the correct format. Can someone guide me how to use the command line arguments for linux to be run correctly in QProcess.It should open the file in desktop directory after connecting with the linux host

Christian Ehrlicher

@Vijaykarthikeyan said in SSH Connection with Remote Linux devices:

not mentioned the correct format

What does this mean? You don't need to re-format the arguments in any way. Just pass them to QProcess::setArguments(). The detailed description also has an example on how to pass arguments.

Vijaykarthikeyan

@Christian-Ehrlicher ok..when i included this after starting the process:

qDebug() << sshProcess->state();

        qDebug() << "SSH Output:" << sshProcess->readAllStandardOutput();
        qDebug() << "SSH Error Output:" << sshProcess->readAllStandardError();

it gives like this:

QProcess::Running
SSH Output: ""
SSH Error Output: ""

why?it is not printing..readAllStandardOutput and readAllStandardError are QBytArrays..

Can I consider this as my program executed correctly?

Because on terminal, when successfully connected and executing the shell scirpt..it runs like this:

python: no process found
No Arduino
connection reset
No Arduino
connection reset
No Arduino

In my Qt,it should print like this

Vijaykarthikeyan

@Vijaykarthikeyan Now,it ic successfully connected,

SSH Output: "Linux pi 6.1.21+ #1642 Mon Apr 3 17:19:14 BST 2023 armv6l\n\nThe programs included with the Debian GNU/Linux system are free software;\nthe exact distribution terms for each program are described in the\nindividual files in /usr/share/doc/*/copyright.\n\nDebian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent\npermitted by applicable law.\n\nWi-Fi is currently blocked by rfkill.\nUse raspi-config to set the country before use.\n\n"

But,when i give the command to navigate to the file directory it says too many arguments

JonB

@Vijaykarthikeyan said in SSH Connection with Remote Linux devices:

why?it is not printing..readAllStandardOutput and readAllStandardError

As I presume you have discovered, you will not receive any output from a subprocess if you ask for it immediately after starting it --- no output has yet been produced. You either need to connect() to readyRead.,.,.(), call waitForReadyRead() (yuck!) or wait until process finished.

But,when i give the command to navigate to the file directory it says too many arguments

For people to help you, don't you think we need to see what "command" you are issuing, how you are issuing it, and just what the error message reads? Or do you think we can tell you what is wrong with your "command to navigate to the file directory" without knowing what you have done?