Using sudo in an SSH Shell Session

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Demonstrates running a command with sudo in a shell session without an interactive prompt. sudo -S reads the password from stdin and -p "" suppresses the prompt, so piping the password in with echo runs the command as root with no interaction.

Security note: The password appears in the command line, so it may be visible in the remote host's process list and shell history. A passwordless sudo rule for the specific command is preferable where it can be arranged.

bool success = false;

//  This example requires the Chilkat API to have been previously unlocked.
//  See Global Unlock Sample for sample code.

//  Demonstrates running a command with "sudo" in a shell session, supplying the password without
//  an interactive prompt.

Chilkat.Ssh ssh = new Chilkat.Ssh();

int port = 22;
success = ssh.Connect("ssh.example.com",port);
if (success == false) {
    Debug.WriteLine(ssh.LastErrorText);
    return;
}

//  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.
string password = "mySshPassword";

success = ssh.AuthenticatePw("mySshLogin",password);
if (success == false) {
    Debug.WriteLine(ssh.LastErrorText);
    return;
}

//  Start a shell session.  QuickShell allocates a PTY, so the shell echoes the commands sent
//  to it and prints a prompt.
int channelNum = ssh.QuickShell();
if (channelNum < 0) {
    Debug.WriteLine(ssh.LastErrorText);
    return;
}

//  Build the command.  "sudo -S" makes sudo read the password from stdin, and "-p" sets the
//  prompt -- setting it to an empty string removes the prompt entirely.  Piping the password in
//  via "echo" therefore runs the command as root with no interaction.
//  
//  Security note: the password appears in the command line, so it can be visible in the remote
//  host's process list and shell history.  Prefer a passwordless sudo rule where possible.
Chilkat.StringBuilder sbCommands = new Chilkat.StringBuilder();
sbCommands.Append("echo \"");
sbCommands.Append(password);
sbCommands.Append("\" | sudo -S -p \"\" ls\n");

//  The final command echoes a marker used to detect the end of the output.  The single quotes
//  around 'IS' are a trick: the terminal echo of the typed command includes the quotes, while
//  the command's actual output does not.  Matching the unquoted form therefore matches the real
//  output rather than the echo.
sbCommands.Append("echo THIS 'IS' THE END OF THE SCRIPT\n");

string commands = sbCommands.GetAsString();
success = ssh.ChannelSendString(channelNum,commands,"utf-8");
if (success == false) {
    Debug.WriteLine(ssh.LastErrorText);
    return;
}

//  No more commands will be sent.
success = ssh.ChannelSendEof(channelNum);
if (success == false) {
    Debug.WriteLine(ssh.LastErrorText);
    return;
}

//  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.ReadTimeoutMs = 15000;

bool caseSensitive = true;
success = ssh.ChannelReceiveUntilMatch(channelNum,"THIS IS THE END OF THE SCRIPT","utf-8",caseSensitive);
if (success == false) {
    Debug.WriteLine(ssh.LastErrorText);
    return;
}

//  Close the channel only after the desired output has been received.
success = ssh.ChannelSendClose(channelNum);
if (success == false) {
    Debug.WriteLine(ssh.LastErrorText);
    return;
}

success = ssh.ChannelReceiveToClose(channelNum);
if (success == false) {
    Debug.WriteLine(ssh.LastErrorText);
    return;
}

string sessionOutput = ssh.GetReceivedText(channelNum,"utf-8");
if (ssh.LastMethodSuccess == false) {
    Debug.WriteLine(ssh.LastErrorText);
    return;
}

Debug.WriteLine("--- output ----");
Debug.WriteLine(sessionOutput);

ssh.Disconnect();