Certain Unix commands fail with "... not found", when executed through Java using JSch even with setPty enabled

Question

I'm creating an android app that sends commands to a linux terminal on a device. I am able to get the proper output when using the "ls" command, however the device does not give me any output when I use "ifconfig" or "iwconfig". Using Tera Term, I have verified these commands do work. I have tried including ((ChannelExec)channel).setPty(true); in order to fix this, however the terminal still appears to not recognise the command. Adding that line of code also changes my output for the "ls" command to something I do not recognise.

This is my JSch code:

package com.example.riot94.whizpacecontroller;
import android.os.AsyncTask;
import android.util.Log;

import java.io.IOException;
import java.io.InputStream;

import com.jcraft.jsch.Channel;
import com.jcraft.jsch.ChannelExec;
import com.jcraft.jsch.JSch;
import com.jcraft.jsch.JSchException;
import com.jcraft.jsch.Session;
/**
 * Created by riot94 on 1/6/2017.
 */

public class JSchConnectionProtocol extends AsyncTask<String, Void, String>{
    private String host;
    private String user;
    private String password;

    public JSchConnectionProtocol(String h, String u, String p){
        host = h;
        user = u;
        password = p;
    }

    @Override
    protected String doInBackground(String... command) {
        String output = "";
        try{
            java.util.Properties config = new java.util.Properties();
            config.put("StrictHostKeyChecking", "no");
            JSch jsch = new JSch();
            Session session=jsch.getSession(user, host, 22);
            session.setPassword(password);
            session.setConfig(config);
            session.setTimeout(10000);
            Log.d("CONNECTION", "Attempting to connect to " + host + " as user: " + user);
            session.connect();
            Log.d("CONNECTION", "Connected to " + host + " as user: " + user);

            Channel channel=session.openChannel("exec");
            ((ChannelExec)channel).setPty(true);
            ((ChannelExec)channel).setCommand(command[0]);
            channel.setInputStream(null);
            ((ChannelExec)channel).setErrStream(System.err);

            output = printOutputAfterXMilliSeconds(channel,1000);

            channel.disconnect();
            session.disconnect();
            Log.d("DONE","DONE");
        }catch(Exception e){
            e.printStackTrace();
        }
        return output;
    }

    private String printOutputAfterXMilliSeconds(Channel channel, int ms) throws IOException, JSchException {
        InputStream in=channel.getInputStream();
        channel.connect();
        String totalOutput = "";
        byte[] tmp=new byte[1024];
        while(true){
            while(in.available()>0){
                int i=in.read(tmp, 0, 1024);
                if(i<0)break;
                String output = new String(tmp, 0, i);
                totalOutput += output;
                Log.d("OUTPUT", output);
            }

            if(channel.isClosed()){
                Log.d("EXIT_STAT","exit-status: "+channel.getExitStatus());
                break;
            }

            try{
                Log.d("PRE-SLEEP","About to sleep");
                Thread.sleep(ms);
                //channel.sendSignal("2");
                Log.d("POST-SLEEP","Slept and woken");
            }catch(Exception ee){
                ee.printStackTrace();
                channel.disconnect();
            }
        }
        return totalOutput;
    }

}

My android app receives an empty String in its activity when I enter

iwconfig

without ((ChannelExec)channel).setPty(true);. With it, my output is:

ash: iwconfig: not found
exit-status: 127

I get a similar result with

ifconfig

My output of the "ls" command with ((ChannelExec)channel).setPty(true);:

[1;34mGUI[0m                            [1;32mmeter.sh[0m
[1;32mReadme4Gui[0m                     [0;0mmeter_iplist.txt[0m
[1;32mami_concentrator_ETH_20120413[0m  [0;0mmeter_list.txt[0m
[1;32mami_demo_qingjun[0m               [0;0mroute.sh[0m
[1;32mami_festtech[0m                   [1;32mscript.sh[0m
[1;32mami_mac[0m                        [1;32msetGateway.sh[0m
[1;32mami_qingjun[0m                    [1;32mspectrmgmt[0m
[1;32mbootup.sh[0m                      [1;32msystem.sh[0m
[1;32mconcentrator.sh[0m                [1;32mtemp1.sh[0m
[1;32mdisFreq.sh[0m                     [1;32mtest.sh[0m
[1;32mdisLinkQuality.sh[0m              [1;32mtest1.sh[0m

My output of the "ls" command without ((ChannelExec)channel).setPty(true);:

GUI
Readme4Gui
ami_concentrator_ETH_20120413
ami_demo_qingjun
ami_festtech
ami_mac
ami_qingjun
bootup.sh
concentrator.sh
disFreq.sh
disLinkQuality.sh
meter.sh
meter_iplist.txt
meter_list.txt
route.sh
script.sh
setGateway.sh
spectrmgmt
system.sh
temp1.sh
test.sh
test1.sh

I am not sure what I am doing wrong, how I can fix this so that I can get the correct output for both the iwconfig/ifconfig and ls commands?

Use command-line SSH client (like `ssh` on *nix or `plink` on Windows) to run these commands: `ssh -T username@host ifconfig`, `ssh -t username@host ifconfig`, `echo ifconfig | ssh -t username@host` and `echo ifconfig | ssh -T username@host`. Which of these work and which not? — Martin Prikryl, Jun 06 '17 at 10:01
Do I understand right that with `((ChannelExec)channel).setPty(true);` you get the same behavior with `ifconfig` as without the `setPty`? — Martin Prikryl, Jun 06 '17 at 10:03
Sorry I don't understand the first comment, I should run `ssh -T username@host ifconfig` and the other commands on an SSH is that it? Will VM linux or Git Bash work? `username` would be my computer's username and `host` would be the IP addr I am trying to connect to, is that right? As for `ifconfig` it gives me the same output `ash: ifconfig: not found` when I run the code individually in Eclipse. In the android app, without `((ChannelExec)channel).setPty(true);` the output is an empty String `""` whereas with `((ChannelExec)channel).setPty(true);`, the output is `ash: ifconfig: not found` — Ryan T., Jun 07 '17 at 01:40
Yes, VM linux or Git bash would do. But you can actually use the commands in SSH terminal of the server itself (connecting back to the host). `username` and `host` are the same username and host that you have in your Java code. - *"As for ifconfig it gives me the same output ash: ifconfig: not found when I run the code individually in Eclipse"* - Not sure what you refer to. Did you actually try the commands I've suggested in Eclipse? And all of them give you that error message? — Martin Prikryl, Jun 07 '17 at 06:04
I edited my question with the results of the commands you suggested above. I'm not too sure what those commands are doing though — Ryan T., Jun 07 '17 at 06:58
I didn't want you to run them in JSch. - How do you run Git Bash? I do not get the problem with *"Pseudo-terminal will not be allocated because stdin is not a terminal."* when I run the commands from Git Bash window. - If you are on Windows, you can use Plink instead of `ssh` from `cmd.exe` console window. - How come you get "connection timeout"? Is the Linux host reachable from the site, where you run the command on? — Martin Prikryl, Jun 07 '17 at 07:17
My Command Prompt does not recognise `Plink` or `plink`. In Git Bash, I just type in the commands above, with the relevant `host` and `user`. Yes, the Linux host is reachable from the site. — Ryan T., Jun 07 '17 at 07:24
I am unable to run the the file, the application closes almost instantly when I try to run it. — Ryan T., Jun 07 '17 at 07:32
It's a console application, you have to run it from a console window (cmd.exe). — Martin Prikryl, Jun 07 '17 at 07:33
For all four commands? (replace `ssh` with `plink` in the commands). — Martin Prikryl, Jun 07 '17 at 08:07
I'm not sure how to run the last 2 commands with `plink`, but the first 2 commands give me `ash: ifconfig: not found` — Ryan T., Jun 07 '17 at 08:22
For clarity, I entered `E:/plink -t root@192.168.1.41 ifconfig` and `E:/plink -t root@192.168.1.41 ifconfig` — Ryan T., Jun 07 '17 at 08:23
Exactly the same way as with `ssh`: `echo ifconfig | E:\plink -t username@host` — Martin Prikryl, Jun 07 '17 at 08:23
The last 2 commands give me: `'E:' is not recognised as an internal or external command, operable program or batch file.` — Ryan T., Jun 07 '17 at 08:26
Show me a screenshot of a whole console window with the error message. — Martin Prikryl, Jun 07 '17 at 08:31
Download and run `PuTTY.exe`, in *Host Name* box, enter `username@host`, go to *Connection > SSH > Kex* and move *"Diffie-Hellman group 1"* above the *"-- warn below here --"* line. And save settings to save session. Try to connect. Confirm the host key. And then with plink do `echo ifconfig | E:\plink store_session_name -t` (and `-T`). — Martin Prikryl, Jun 07 '17 at 11:49
I'm getting the error `-ash: plink: not found`. Am I supposed to download plink on to the device I am trying to connect to? If yes, is there a way I can transfer the app on my computer onto the device? The device cannot be connected to the internet. — Ryan T., Jun 08 '17 at 02:37
Show us a screenshot of TeraTerm or PuTTY showing how you execute the `ifconfig`. — Martin Prikryl, Jun 08 '17 at 03:39
It works! Thank you! So the issue was that I was not accessing the directory the command was in, is that correct? — Ryan T., Jun 08 '17 at 05:59

score 3 · Accepted Answer · answered Jun 08 '17 at 06:34

Your server/shell is misconfigured somehow. It does not set the PATH correctly, when a shell session is not started. That's, why the ifconfig/iwconfig binaries cannot be found.

Either fix your startup scripts to set the PATH correctly for all situations. Or use a full path to the ifconfig/iwconfig.

To find the full path, open a regular shell session using your SSH client and type:

which ifconfig

For a similar issue, see Certain Unix commands fail with "... not found", when executed through Java using JSch.

Certain Unix commands fail with "... not found", when executed through Java using JSch even with setPty enabled

1 Answers1

Linked