Unix commands become, cd and ls -la to be run via java code

Question

I am supposed to connect to a Unix server, then go to the specific folder(which has got access restrictions) and fetch the file details from there. For the same , the code that I have written is

try{

            Session session = new JSch().getSession("username", "host"); 
            session.setPassword("password");
            java.util.Properties config = new java.util.Properties(); 
            config.put("StrictHostKeyChecking", "no");
            session.setConfig(config);
            session.connect();

            Channel channel=session.openChannel("exec");
            ((ChannelExec)channel).setCommand("cd a/b/node01/c.ear && ls -la");
            channel.connect();
            channel.run();
            InputStream in = channel.getInputStream();

            System.out.println(channel.isConnected());

            byte[] tmp = new byte[1024];
            while (true)
            {
              while (in.available() > 0)
              {
                int i = in.read(tmp, 0, 1024);
                if (i < 0)
                  break;
                System.out.print(new String(tmp, 0, i));
              }
              if (channel.isClosed())
              {
                System.out.println("exit-status: " + channel.getExitStatus());
                break;
              }

            }



            channel.disconnect();
            session.disconnect();
        }
        catch(Exception exception){
            System.out.println("Got exception "+exception);
        }

I am not getting the list of files that are present in the location supplied. The output that I am getting is

true

exit-status: 1

How do I get the desired output?

Is "cd a/b/node01/" really pointing to a valid directory? Have you tried absolute paths? — GhostCat
– GhostCat, Commented Jun 23, 2017 at 8:19
Yes that's a valid directory. When I go to the same via Putty, I get to see the files in the directory after issuing ls -la command. — Random Coder
– Random Coder, Commented Jun 23, 2017 at 8:20
Even with the SFTP, I am getting the permission denied error since the directory in which ls -la command is to be issued is restricted directory. — Random Coder
– Random Coder, Commented Jun 27, 2017 at 4:12

Martin Prikryl · Accepted Answer · 2025-03-13 06:50:27Z

1

Do not use shell commands to retrieve file information. Use SFTP!

Channel channel = session.openChannel("sftp");
channel.connect();

ChannelSftp c = (ChannelSftp)channel;
java.util.Vector vv = c.ls("/a/b/node01/c.ear");

for (int i = 0; i < vv.size(); i++)
{
    System.out.println(vv.elementAt(i).toString());
}

See http://www.jcraft.com/jsch/examples/Sftp.java.html (link to archive)

Regarding your code for "exec" channel:

First, the code has a recurring flaw described in:
Randomly getting empty output while executing shell command via JSch.
Though to actually debug your problem, you have to read both stdout and stderr to collect any errors (which you are obviously getting).
For that see Log stdout and stderr from ssh command in the same order it was created.

edited Mar 13 at 6:50

answered Jun 23, 2017 at 8:21

Martin Prikryl

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Comments

Henry · Accepted Answer · 2017-06-23 08:25:47Z

0

A possible problem here is the usage of in.available(). It returns the number of bytes that can be read without blocking.

The correct way to read a stream until eof is:

byte[] buf = new byte[1024];
int len;
while ((len=in.read(buf)) >= 0) {
   // do something with buf[0 .. len]
}

answered Jun 23, 2017 at 8:25

Henry

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