Chilkat2-Python

Release an SSH Channel's Local Resources

Demonstrates the Chilkat Ssh.ChannelRelease method, which releases Chilkat's retained local resources for a channel after all output and exit information has been retrieved. The only argument is the channel number.

Background: Chilkat retains a channel's buffered output and exit information after the channel closes, so you can still read a command's final output. That retention costs memory, and a long-running program that opens many channels should release each one when finished with it. Note this is not a channel-closing method — it sends neither EOF nor CLOSE. Retrieve everything you need first, because releasing discards it.

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import sys
import chilkat2

success = False

# Demonstrates the Ssh.ChannelRelease method, which releases Chilkat's retained local resources
# for a channel after all output and exit information has been retrieved.  The only argument is
# the channel number.

ssh = chilkat2.Ssh()

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()

success = ssh.SendReqExec(channelNum,"uname -a")
if (success == False):
    print(ssh.LastErrorText)
    sys.exit()

# IMPORTANT: Set a read timeout.  ReadTimeoutMs defaults to 0, which means no limit -- without
# it, this call waits forever if the server never sends channel close.
ssh.ReadTimeoutMs = 15000

# Retrieve everything of interest before releasing the channel.
success = ssh.ChannelReceiveToClose(channelNum)
if (success == False):
    print(ssh.LastErrorText)
    sys.exit()

output = ssh.GetReceivedText(channelNum,"utf-8")
if (ssh.LastMethodSuccess == False):
    print(ssh.LastErrorText)
    sys.exit()

print(output)

# Release the retained local resources.  This does not send EOF or CLOSE.
ssh.ChannelRelease(channelNum)

ssh.Disconnect()