Sometimes, we need to run a simple command on a remote machine over SSH. For example, we need to query the remote machine's CPU or RAM information. This can be done from a Python script as shown in this recipe.
You need to install the third-party package, Paramiko, as shown in the following command, from the source available from GitHub's repository at https://github.com/paramiko/paramiko:
$ pip install paramiko
We can use the paramiko module to create a remote session to a Unix machine.
Then, from this session, we can read the remote machine's /proc/cpuinfo file to extract the CPU information.
Listing 7.3 gives the code for printing a remote machine's CPU information, as follows:
#!/usr/bin/env python
# Python Network Programming Cookbook -- Chapter - 7
# This program is optimized for Python 2.7.
# It may run on any other version with/without modifications.
import argparse
import getpass
import paramiko
RECV_BYTES = 4096
COMMAND = 'cat /proc/cpuinfo'
def print_remote_cpu_info(hostname, port, username, password):
client = paramiko.Transport((hostname, port))
client.connect(username=username, password=password)
stdout_data = []
stderr_data = []
session = client.open_channel(kind='session')
session.exec_command(COMMAND)
while True:
if session.recv_ready():
stdout_data.append(session.recv(RECV_BYTES))
if session.recv_stderr_ready():
stderr_data.append(session.recv_stderr(RECV_BYTES))
if session.exit_status_ready():
break
print 'exit status: ', session.recv_exit_status()
print ''.join(stdout_data)
print ''.join(stderr_data)
session.close()
client.close()
if __name__ == '__main__':
parser = argparse.ArgumentParser(description='Remote file copy')
parser.add_argument('--host', action="store", dest="host",
default='localhost')
parser.add_argument('--port', action="store", dest="port",
default=22, type=int)
given_args = parser.parse_args()
hostname, port = given_args.host, given_args.port
username = raw_input("Enter the username:")
password = getpass.getpass("Enter password for %s: " %username)
print_remote_cpu_info(hostname, port, username, password)Running this script will show the CPU information of a given host, in this case, the local machine, as follows:
$ python 7_3_print_remote_cpu_info.py Enter the username:faruq Enter password for faruq: exit status: 0 processor : 0 vendor_id : GenuineIntel cpu family : 6 model : 42 model name : Intel(R) Core(TM) i5-2400S CPU @ 2.50GHz stepping : 7 cpu MHz : 2469.677 cache size : 6144 KB fdiv_bug : no hlt_bug : no f00f_bug : no coma_bug : no fpu : yes fpu_exception : yes cpuid level : 5 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 syscall nx rdtscp lm constant_tsc up pni monitor ssse3 lahf_lm bogomips : 4939.35 clflush size : 64 cache_alignment : 64 address sizes : 36 bits physical, 48 bits virtual power management:
First, we collect the connection parameters such as hostname, port, username, and password. These parameters are then passed to the
print_remote_cpu_info() function.
This function creates an SSH client session by calling the transport class of paramiko. The connection is made thereafter using the supplied username and password. We can create a raw communication session using open_channel() on the SSH client. In order to execute a command on the remote host, exec_command() can be used.
After sending the command to the remote host, the response from the remote host can be caught by blocking the recv_ready() event of the session object. We can create two lists, stdout_data and stderr_data, and use them to store the remote output and error messages.
When the command exits in the remote machine, it can be detected using the exit_status_ready() method, and the remote session data can be concatenated using the join() string method.
Finally, the session and client connection can be closed using the close() method on each object.