Paramiko with continuous stdout

Question

I use Paramiko to run some ssh commands to the remote Linux server. The commands will have continuous output in the console and I want to print these all information in the local console window.

stdin, stdout, stderr = ssh.client.exec_command("ls")
for line in stdout.read()
    print line,
ssh.client.close()

So if I write the code like this, all the output information will be sent back to me until the command finishes executing while I want to print the output in live.

Thanks a lot.

Answer 1

Of course there is a way to do this. Paramiko exec_command is async, buffers are filled while data arrives regardless of your main thread.

In your example stdout.read(size=None) will try to read the full buffer size at once. Since new data is always arriving, it won't ever exit. To avoid this, you could just try to read from stdout in smaller chunks. Here's an example that reads buffers bytewise and yields lines once a \n is received.

stdin,stdout,stderr = ssh.exec_command("while true; do uptime; done")

def line_buffered(f):
    line_buf = ""
    while not f.channel.exit_status_ready():
        line_buf += f.read(1)
        if line_buf.endswith('\n'):
            yield line_buf
            line_buf = ''

for l in line_buffered(stdout):
    print l

You can increase performance by tweaking the code to use select.select() and by having bigger chunk sizes, see this answer that also takes into account common hang and remote command exit detection scenarios that may lead to empty responses.

Answer 2

So because sharing is caring , I resolved the issue for the PARAMIKO with continuous output like this (ignore the index and replace stuff, issues proprietary to my device):

"elif action == "icmd":
        cmd = command
        channel = ssh.get_transport().open_session()
        channel.exec_command(cmd)
        channel.set_combine_stderr(True)
        index = 0
        a = ""  # list to be filled with output of the commands.
        while True:
            if channel.exit_status_ready():
                break
            o = channel.recv(2048).decode("utf-8")
            if o:
                a += o
                if "\n" in o:
                    b = a.split("\n")
                    a = b[-1]
                    b.pop()
                    for x in b:
                        print(x.replace("●", "").replace("└─", ""), flush=True)
                        index += 1
                if index == 0 and len(o) > 0:
                    print(o.replace("●", "").replace("└─", ""), flush=True)
                if index == 0 and len(o) == 0:
                    print(f"Your command '{cmd}' did not returned anything! ")
        channel.close()
        ssh.close()

"

I chose the split and pop things because when using commands like : traceroute www.google.com , for example, the output was splited into separate rows.

Also, I integrated a shell, for interactive input/output with the device, like this :

elif action == "shell":
        channel = ssh.invoke_shell()
        cmd = command
        print("Shell started")
        print(channel.recv(2048).decode())
        while True:
            if channel.exit_status_ready():
                print("Session Ended!")
                break
            try:
                cmd = input(cmd)
                channel.send(f"{cmd}\n".encode())
                time.sleep(1)
                output = channel.recv(2048).decode("utf-8")
                print(output.replace("●", "").replace("└─", ""), flush=True)
                if cmd == "exit":
                    break
            except KeyboardInterrupt:
                break
        channel.close()
        ssh.close()

Enjoy it !