CkPython

Start a Remote Shell over SSH

Demonstrates the Chilkat Ssh.SendReqShell method, which starts a remote shell on an open session channel. The only argument is the channel number. This example starts a shell without a PTY, which is the recommended approach for scripting, and streams a command whose output ends with a marker.

Background: A shell request starts the account's login shell and leaves the channel open for ongoing input and output — the difference from exec, which runs a single command. When no PTY is requested, the shell detects it is attached to a raw pipe rather than a terminal and runs non-interactively: it prints no command prompt, does not echo the commands you send, and skips interactive login scripts. That yields clean, easily parsed output, but it also means there is no prompt to synchronize on — have each command echo a predictable marker, or rely on EOF and the channel exit status, to know when its output is complete.

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import sys
import chilkat

success = False

#  Demonstrates the Ssh.SendReqShell method, which starts a remote shell on an open session
#  channel.  The only argument is the channel number.  A shell can be started without a PTY,
#  which is the recommended approach for scripting and automation.

ssh = chilkat.CkSsh()

sshPort = 22
success = ssh.Connect("ssh.example.com",sshPort)
if (success == False):
    print(ssh.lastErrorText())
    sys.exit()

#  Normally you would not hard-code the password in source.  You should instead obtain it
#  from an interactive prompt, environment variable, or a secrets vault.
password = "mySshPassword"

success = ssh.AuthenticatePw("mySshLogin",password)
if (success == False):
    print(ssh.lastErrorText())
    sys.exit()

#  Open a session channel.  A negative return value indicates failure.
channelNum = ssh.OpenSessionChannel()
if (channelNum < 0):
    print(ssh.lastErrorText())
    sys.exit()

#  Start a shell WITHOUT requesting a PTY.  Without a PTY the shell sees it is connected to a
#  raw data pipe and enters non-interactive mode: it suppresses the command prompt, does not
#  echo typed commands back, and skips interactive login scripts.  The output is therefore
#  clean and easily parseable -- but because no prompt is ever sent, code must not wait for
#  one.  Instead, have each command print a predictable marker, or wait for EOF / channel close.
success = ssh.SendReqShell(channelNum)
if (success == False):
    print(ssh.lastErrorText())
    sys.exit()

print("Remote shell started.")

#  Multiple commands can now be streamed into the shell, one after another.  Each command
#  echoes a marker so the code can tell when its output is complete.
success = ssh.ChannelSendString(channelNum,"uname -a; echo DONE_MARKER\n","utf-8")
if (success == False):
    print(ssh.lastErrorText())
    sys.exit()

#  IMPORTANT: Set a read timeout before receiving until a match.  ReadTimeoutMs defaults to 0,
#  which means no limit -- without it, this call waits forever if the received data never
#  contains a match.
ssh.put_ReadTimeoutMs(15000)

caseSensitive = False
success = ssh.ChannelReceiveUntilMatch(channelNum,"DONE_MARKER","utf-8",caseSensitive)
if (success == False):
    print(ssh.lastErrorText())
    sys.exit()

output = ssh.getReceivedText(channelNum,"utf-8")
if (ssh.get_LastMethodSuccess() == False):
    print(ssh.lastErrorText())
    sys.exit()

print(output)

ssh.Disconnect()