Develop Reference

Python SSH iteration through different paths

I've got a JSON object which looks like this:
{UID_1:{
jumpboxes:[jump_ip1, jump_ip2,...],
hosts: [host_ip1, host_ip2,...],
...},
UID_2:{...
The authentication to the jumpboxes is via kerberos (passwordless), the authentication to the hosts is with password and the hosts are only visible via the jump hosts. I don't know out of the list of IPs which ones work, which are stuck, or non-responding, etc. so I need to find the first path that would let me open an SSH session.
What I can do is check for the exit codes when ssh-ing to the jump hosts with something like this:
jumpip = ''
for i in json[uid][jumpboxes]:
if os.system('ssh {}#{}'.format(username,i))>0:
continue
else:
jumpip = i
break
This gives me the first working jumpbox ip without issues, however having a password to establish a ssh connection with the second host isn't as easy to check for the exit code of.
There're multiple ways to open the tunnel - either with os.system() and using sshpass with a session proxy (something like:
if os.system('sshpass -p {} ssh -o ProxyCommand="ssh {}#{} nc {} 22" {}#{} -t {}'.format(password, user, jumpip, hosts[j], user, hosts[j], remote_cmd))>0:.... (for context let's assume the sshpass command will look something like this: sshpass -p Password123! -o ProxyCommand="ssh user#jumpbox nc hostip 22" user#hostip -t ll or doing pint in a subshell with something like os.system('ssh user#jumpbox -t ping {} -c 5'.format(hosts[j])) and although ping would return an exit code, ICMP echo replies don't mean I'd be able to open a tunnel (e.g the daemon can be stuck or could have crashed, etc.), or I can do a try-except-else block, that tries to open an ssh session to the remote host via the jumpbox with pexpect or with subrpocess.popen and with piping the stdio thus allowing me to push the password and if that fails to raise a custom exception, but I can't figure out how to get the exitcode from the ssh client, so I can check for the status...
Neither of these is robust enough for me, so I'd rather iterate through the IPs correctly, for which I'm open for suggestions.
A little bit of background - the tunnel would be used to start a nohup-ed command and then will be closed. The script uses multiprocessing and pool to go through a whole bunch of these, so I'll start them and then have a loop to check their status and retrieve the result of the remote script executed on the hosts. I know os.system is deprecated and I should use subprocess, but this isn't essential for the use-case so I don't really care about this. I'm looking for a smart way how to iterate through the possible paths which will take given a list with jumpbox with length n and a list with hosts with length m and timeout x seconds max of n*m*x seconds to figure out and instead shorten that time.
I'm also using pexpect(which uses paramiko itself) for the interactions with the remote hosts, once I've found the correct IPs I need to open the tunnel with.
Thanks in advance!

Paramiko's exit_status_ready function will tell you the exit status.
Return true if the remote process has exited and returned an exit
status. You may use this to poll the process status if you don’t want
to block in recv_exit_status. Note that the server may not return an
exit status in some cases (like bad servers).
Looking at the source code for pexpect, I don't see where it uses Paramiko, so you may need to replace all of your pexpect code with Paramiko code. Paramiko gives you a lot of control over all of the low level aspects of establishing an SSH connection, so it can be a little rough to figure out, but it does give you a lot of control over the entire process.

I figured it out - pexpect offers an exit code if there's a prompt, i.e. I did something along the lines of
host = ''
for i in hosts:
cmd = 'ssh {}#{} -t ssh {}'.format(user,jumpbox, i)
try:
p = pexpect.spawn(cmd)
if p.expect('.*') == 0:
host = i
break
except:
someException()
if host != '':
...
Thanks for all the input.

Python raw_input malfunctions and returns -bash: line 1: <INPUT>: command not found

I have written a script that establishes an SSH tunnel and connects to a database over that tunnel.
Extremely simplified nutshell (obvious parameters and extra logic omitted):
sshTunnelCmd = "ssh -N -p %s -L %s:127.0.0.1:%s -i %s %s#%s" % (
sshport, localport, remoteport, identityfile, user, server
)
args = shlex.split(sshTunnelCmd)
tunnel = subprocess.Popen(args)
time.sleep(2)
con = MySQLdb.connect(host="127.0.0.1", port=localport, user=user, passwd=pw, db=db)
## DO THE STUFF ##
con.close()
tunnel.kill()
The shell-equivalent commands are below, and I have tested both the commands and the script to work in "clean client" conditions, i.e. after a reboot.
ssh -N -p 22 -L 5000:127.0.0.1:3306 user#server
mysql --port 5000 -h 127.0.0.1 -u dbuser -p
SSH login is with keys and in ~/.ssh/config the server is configured as
Host server
Hostname F.Q.D.N
Port 22
User user
ControlMaster auto
ControlPath ~/.ssh/master-%r#%h:%p
ControlPersist 600
IdentityFile ~/.ssh/id_rsa
In the ## DO THE STUFF ## section there is code that tries to connect to the database as regular users. If an exception is raised, it asks for manual input of root credentials, creates the regular users and continue to do the stuff (ordinary queries, all tested manually and working in the python code under clean client conditions).
ruz = raw_input('root user? ')
print (ruz)
rup = raw_input('root password? ')
print (rup)
print ("Root connecting to database.")
try:
cxroot = MySQLdb.connect(host=host, port=port, user=ruz, passwd=rup)
cur = cxroot.cursor()
except MySQLdb.Error, e:
print ("Root failed, sorry.")
print "Error %d: %s" % (e.args[0],e.args[1])
print ("GAME OVER.")
return -1
Under clean client, the first and some subsequent executions work well, including when I try to test the script robustness and remove the user server-side. However, at some point, it hangs in a weird way after the second raw_input in the code block above. Output:
root user? root
root
root password? s3cReTsTr1n9
-bash: line 1: s3cReTsTr1n9: command not found
The only thing I can do at this point is kill the process or hit CTRL+C, which is followed by the following traceback:
^CTraceback (most recent call last):
File "./initdb.py", line 571, in <module>
main()
File "./initdb.py", line 526, in main
connection = connectDB ('127.0.0.1', localport, dbuser, dbpw, db)
File "./initdb.py", line 128, in connectDB
rup = raw_input('root password? ')
KeyboardInterrupt
Another unexpected symptom I noticed is that keyboard input to the terminal window (I am running this in a bash terminal within Xubuntu 14.04LTS) becomes spuriously unresponsive, so I have to close the terminal tab and start a new tab. This clears keyboard input, but not script behaviour.
I have tried to search for a solution but the usual search engines are not helpful in my case, probably because I do not completely understand what is going on. I suspect that keyboard input is somehow redirected to a process, possibly the tunnel subprocess, but I cannot explain why the first raw_input works as expected and the second one does not.
I am also uncomfortable with the way I create the tunnel, so any advice for a more robust tunnel creation is welcome. Specifically, I would like to have more fine grained control over the tunnel creation, rather than waiting an arbitrary two seconds for the tunnel to be established because I have no feedback from that subprocess.
Thanks for sharing your time and expertise.

There's two sections to my answer: how I'd go about diagnosing this, and how I would go about doing this.
To begin with, I'd suggest using the prompt that's failing as an opportunity to do some exploration.
There's two approaches you could take here:
Just enter hostname (or whatever) to find out where it's running
Enter bash, or if the remote end has an X server add -X to your ssh command then type a terminal program (xterm, gnome-terminal, etc). In your new shell you can poke around to see what's going on.
If you determine it's running on the client side you could diagnose it with strace:
strace -f -o blah.log yourscript.py
... where you'd enter an easy to search string for the password then search for that in blah.log. Because of the -f flag it will print the PID of the process that attempted to execute it; backtracking from there you'll probably find that PID started with a fork from another PID. That PID is what tried to execute it, so you should be able to investigate from there.
As for how I'd do this: I'm still fairly new to python so I would've been inclined to use perl or expect. Down the perl path you might look at:
Net::SSH::Tunnel; this is probably the first one I'd look at using.
Use open or open3 then do something hacky like:
wait for stdout on the process to have text available; you'd have to get rid of -N for that, and you'd be at the mercy of remote auto-logout.
One of the various responses to ssh-check-if-a-tunnel-is-alive
Net::SSH::Expect (eg this post, though I didn't look at his implementation so you'd have to make your own choice on that). This or the "real" expect are probably overkill but you could find a way I'm sure.
Although ruby has a gem like perl's Net::SSH::Tunnel, I don't see a pip for python. This question and this one both discuss it and they seem to indicate you're limited to either starting it as a sub-process or using paramiko.

Are you free to configure the server as you like?
Then try a vpn connection instead of ssh port forwarding. This will easier reconnect without affecting your application, so the tunnel may be more stable.
For the raw_input problem i cannot see why it happens, but maybe the ssh command in a shell interferes with your terminal? If you really want to integrate the ssh tunnel you may want to look at some python modules for handling ssh.

-bash: line 1: s3cReTsTr1n9: command not found
I got same error as -bash command not found even though I was just accepting raw_input() / input(). I tried this in both 2.7 and 3.7 version.
I was trying run a client server program on same mac machine. I had two files server.py and client.py. Everytime in the terminal, I first ran the server.py in background and then ran client.py.
Terminal 1: python server.py &
Terminal 2: python client.py
Each time I got the error "-bash: xxxx: command not found". xxxx here is whatever input I gave.
Finally after spending 5 hours on this I stopped running server.py in background.
Terminal 1: python server.py
Terminal 2: python client.py
And viola it worked. raw_input and input did not give me this error again.
I am not sure if this helps. But this is the only post I found on internet which had exactly the same issue as mine. And thought maybe this would help.

Use the same SSH object to issue "exec_command()" multiple times in Paramiko

I want to use the same SSH object to issue exec_command() multiple times in Paramiko module in Python.
The objective is to get output from the same session.
Is there a way to do it? The exec_command() closes channel once it completes executing a command and thereafter a new ssh object is needed to execute a following command .. but the sessions will differ which I do not want.
Code
import os, sys,
import connectlibs as ssh
s = ssh.connect("xxx.xx.xx.xxx", "Admin", "Admin")
channel = s.invoke_shell()
channel.send("net use F: \\\\xyz.xy.xc.xa\\dir\n")
>>>32
channel.send("net use")
>>>7
channel.recv(500)
'Last login: Tue Jun 2 23:52:29 2015 from xxx.xx.xx.xx\r\r\n\x1b]0;~\x07\r\r\n\x1b[32mAdmin#WIN \x1b[33m~\x1b[0m\r\r\n$ net use F: \\\\xyz.xy.xc.xa\\dir\r\nSystem error 67 has occurred.\r\r\n\r\r\nThe network name cannot be found.\r\r\n\r\r\n\x1b]0;~\x07\r\r\n\x1b[32mAdmin#WIN \x1b[33m~\x1b[0m\r\r\n$ net use'
>>>

An SSH session can have multiple channels indeed (but Paramiko possibly does not support it).
But by a session you seem to imagine a "shell session". But that's not what the SSH session is. A channel is actually, what corresponds to a "shell session".
In other words, even if you could open multiple "exec" channels with Paramiko over the same SSH connection (session) and call the exec_command on these, the commands get executed in a different shell session. So it won't help you.
You can test this with PuTTY SSH client. The recent versions support connection sharing, what basically means that you can have more PuTTY windows (each using its own channel) over a single SSH connection/session. If you execute a command in one PuTTY window, and the commands changes an environment (like an environment variable or a current working directory), the change won't get reflected to the other PuTTY window, even if they share the same SSH connection.
So you need to execute the commands in one channel. Depending on your needs (which are still not clear), you need to use the "exec" or the "shell" channel.
In either case you will have troubles determining, where output of one command ends and output of other command starts as they share the same "stream".
You can solve that by inserting a unique separator (string) in between and search for it in the channel output stream.
channel = ssh.invoke_shell()
channel.send('ls\n')
channel.send('echo unique-string-separating-output-of-the-commands\n')
channel.send('pwd\n')

If I run the following script, will my ssh session not be terminated?

So I wrote this script called py_script.py that I ran over an ssh session on a school machine:
import time
import os
while True:
os.system("echo still_alive")
time.sleep(60)
... by doing:
bash $ python py_script.py &.
Is this going to prevent the dreaded broken pipe message from happening?
The problem is, after a period of inactivity when I am over an ssh connection, my connection will be dropped. To prevent this, I wrote the above script that automatically writes a message to the console to count for an "action" so that I don't have to press enter every 5 minutes. (I'm idle on a machine and need to run a process for a good amount of time.)

If your connection is timing out then it is more advisable to look at SSH configuration options which can keep your connection alive.
As a starter example, put the following in a file called ~/.ssh/config:
Host *
ServerAliveInterval 20
TCPKeepAlive=yes
You can read more here.

Paramiko simulate ssh -t option

I instantiate a paramiko channel, then I execute a command and get its output:
channel = transport.open_session()
channel.exec_command('service myservice restart')
stdout = channel.makefile('rb')
for line in stdout:
print line,
However, after executing the command (which finishes), the output iterating gets blocked.
I tested with ssh:
ssh myhost service myservice restart # terminal gets blocked
ssh -t myhost service myservice restart # OK
So I want to simulate the "-t" option in paramiko. So far I tried:
channel = transport.open_session()
channel.get_pty()
channel.invoke_shell()
stdin, stdout = channel.makefile('wb'), channel.makefile('rb')
stdin.write('service myservice restart\n')
for line in stdout:
print line,
But now, stdout doesn't get closed, and the for never ends.
Any ideas?

It appears like invoke_shell() returns a Channel, and it looks like Channels require that you close them explicitly. I would attempt to close some of the channels you're opening, in particular the one returned by invoke_shell().

Have a look at the script that youre trying to run- see if there are any lines like this
/dev/null 2>&1
Im having the same issue as you- in my case trying to remotely run a bitnami control script. Something in your post jogged my memory and reminded me of the output redirections that are in the control script (these caused me some major headache before).
Generally theyre used to either ignore errors or maybe log them somewhere specific- I havent had a chance to try yet, but maybe either piping them back out at the end of the script or if you dont care about the response maybe even manually redirecting some created data out >&2 would work.