Execute command and wait for it to finish with Python Paramiko

Question

I wrote this code in Paramiko:

ssh = SSHClient()
ssh.set_missing_host_key_policy(AutoAddPolicy())
ssh.connect(hostname, username=user, password=passwd, timeout=3)

session = ssh.invoke_shell()
session.send("\n")

session.send("echo step 1\n")
time.sleep(1)

session.send("sleep 30\n")
time.sleep(1)

while not session.recv_ready():
    time.wait(2)

output = session.recv(65535)

session.send("echo step 2\n")
time.sleep(1)

output += session.recv(65535)

I'm trying execute more commands on my Linux server. The problem is my Python code not wait to finish execute command, for example if I'm try to execute sleep 30, the Python not wait 30 seconds for finish execute commands. How can resolve this problem ? I tried with while recv_ready(), but it still does not wait.

Community · Accepted Answer · 2017-03-20 10:18:21Z

11

Use exec_command: http://docs.paramiko.org/en/1.16/api/channel.html

stdin, stdout, stderr = ssh.exec_command("my_long_command --arg 1 --arg 2")

The following code works for me:

from paramiko import SSHClient, AutoAddPolicy
import time
ssh = SSHClient()
ssh.set_missing_host_key_policy(AutoAddPolicy())
ssh.connect('111.111.111.111', username='myname', key_filename='/path/to/my/id_rsa.pub', port=1123)
sleeptime = 0.001
outdata, errdata = '', ''
ssh_transp = ssh.get_transport()
chan = ssh_transp.open_session()
# chan.settimeout(3 * 60 * 60)
chan.setblocking(0)
chan.exec_command('ls -la')
while True:  # monitoring process
    # Reading from output streams
    while chan.recv_ready():
        outdata += chan.recv(1000)
    while chan.recv_stderr_ready():
        errdata += chan.recv_stderr(1000)
    if chan.exit_status_ready():  # If completed
        break
    time.sleep(sleeptime)
retcode = chan.recv_exit_status()
ssh_transp.close()

print(outdata)
print(errdata)

Please note that command history cannot be executed with ssh as is. See example here: https://superuser.com/questions/962001/incorrect-output-of-history-command-of-ssh-how-to-read-the-timestamp-info-corre

edited Mar 20, 2017 at 10:18

CommunityBot

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answered Dec 9, 2015 at 14:33

baldr

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2 Comments

selfmarket.net Over a year ago

i need use invoke_shell because whit exec_command not return output complete

Martin Prikryl Over a year ago

This code can indeed lose some output. You need to test the exit_status_ready before reading (but exit only after reading). See for example stackoverflow.com/q/66191219/850848. Though see my answer for a simpler solution.

Martin Prikryl · Accepted Answer · 2022-02-24 13:49:08Z

In case you do not need to read the stdout and stderr separately, you can use way more straightforward code:

stdin, stdout, stderr = ssh_client.exec_command(command)
stdout.channel.set_combine_stderr(True)
output = stdout.readlines()

The readlines reads until the command finishes and returns a complete output.

In case you need the output separately, do not be tempted to remove the set_combine_stderr and call readlines on stdout and stderr separately. That might deadlock. See Paramiko ssh die/hang with big output

For a correct code that reads the outputs separately, see Run multiple commands in different SSH servers in parallel using Python Paramiko.

Obligatory warning: Do not use AutoAddPolicy – You are losing a protection against MITM attacks by doing so. For a correct solution, see Paramiko "Unknown Server".

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