SSH Output always empty

Question

I've been trying to figure out this problem for hours now and I cant seem to figure it out. I'm trying to use JSch to SSH to a Linux computer from an Android phone. The commands always work fine but the output of the channel is usually empty. Sometimes it displays the output but most of the time it doesn't. Here's the code that I found online.

       String userName = "user";
       String password = "test123";
       String connectionIP = "192.168.1.13";

       JSch jsch = new JSch();
       Session session;
       session = jsch.getSession(userName, connectionIP, 22);
       session.setPassword(password);

       // Avoid asking for key confirmation
       Properties prop = new Properties();
       prop.put("StrictHostKeyChecking", "no");
       session.setConfig(prop);
       session.connect();

       // SSH Channel

       ChannelExec channelssh = (ChannelExec) session.openChannel("exec");      
       ByteArrayOutputStream baos = new ByteArrayOutputStream();
       channelssh.setOutputStream(baos);

       // Execute command
       channelssh.setCommand("ls");
       channelssh.connect();        
       channelssh.disconnect();

       RESULT = baos.toString();

RESULT is usually empty. If I change the command to mkdir or something of that nature the files show up on the Linux computer which leads me to believe that the command part is working correctly. The problem seems to lie within the ByteArrayOutputStream. I've also tested the connectionip, username and password on a different computer through Terminal so I know the credentials are correct. I've Googled this problem to death, any input would help me out significantly!

What does "output is usually empty" mean? Think about which commands gives you output and and which do not. Does ls show anything if you login locally as user? Might it be a test account with an empty home directory? — Kjell Andreassen
– Kjell Andreassen, Commented Feb 13, 2013 at 21:47
The String value of output is "". I am logging on as user I just got rid of that information for this question. When I run ls from the Linux computer itself a lot of files show up in terminal, it just won't show up in this code. I've tried lots of other commands in place of ls as well to no avail. — John P.
– John P., Commented Feb 13, 2013 at 22:19

John P. · Accepted Answer · 2013-02-14 20:58:51Z

3

Found the answer I was reading the wrong stream. Heres the proper code for others with this problem.

       InputStream inputStream = channelssh.getInputStream(); 

       BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));

       StringBuilder stringBuilder = new StringBuilder();

       String line;

       while ((line = bufferedReader.readLine()) != null) 
       {

           stringBuilder.append(line);
           stringBuilder.append('\n');

       }

       return stringBuilder.toString();

answered Feb 14, 2013 at 20:58

John P.

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ymnk · Accepted Answer · 2013-02-14 06:18:08Z

0

The exec-channel will be run on the other thread, so you need to wait for its termination before invoking Channel#disconnect().

answered Feb 14, 2013 at 6:18

ymnk

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