SSH Commands that Prompt for Input, such as su

See more SSH Examples

Demonstrates running a shell command that prompts for additional input, using su as the example. The technique is: send the command, read until the expected prompt appears, then send the response exactly as though it were typed.

Note: This example deliberately requests a PTY. su reads its password from a controlling terminal and refuses to run without one, so a pseudo-terminal is genuinely required here.

bool success = false;

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

//  Demonstrates running a shell command that prompts for additional input, using "su" as the
//  example.  The technique is: send the command, read until the expected prompt, then send the
//  response as though it were typed.
//  
//  Note: This example deliberately DOES request a PTY.  "su" reads its password from a
//  controlling terminal and refuses to run without one, so a pseudo-terminal is required here.

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

string hostname = "ssh.example.com";
int port = 22;
success = ssh.Connect(hostname,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;
}

int channelNum = ssh.OpenSessionChannel();
if (channelNum < 0) {
    Debug.WriteLine(ssh.LastErrorText);
    return;
}

//  Request a pseudo-terminal.  A "dumb" terminal avoids ANSI escape sequences in the output.
string termType = "dumb";
int widthInChars = 120;
int heightInChars = 40;
int pixWidth = 0;
int pixHeight = 0;
success = ssh.SendReqPty(channelNum,termType,widthInChars,heightInChars,pixWidth,pixHeight);
if (success == false) {
    Debug.WriteLine(ssh.LastErrorText);
    return;
}

success = ssh.SendReqShell(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;

//  Send the su command.  Linux/UNIX servers generally expect a bare LF, not a CRLF.
success = ssh.ChannelSendString(channelNum,"su\n","utf-8");
if (success == false) {
    Debug.WriteLine(ssh.LastErrorText);
    return;
}

//  Read until su prompts for the password.
success = ssh.ChannelReceiveUntilMatch(channelNum,"Password:","utf-8",caseSensitive);
if (success == false) {
    Debug.WriteLine(ssh.LastErrorText);
    return;
}

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

Debug.WriteLine(cmdOutput);

//  Send the root password, exactly as if it were typed at the prompt.  Like the login password,
//  this should come from a secure source rather than being hard-coded.
string suPassword = "myRootPassword";
success = ssh.ChannelSendString(channelNum,suPassword,"utf-8");
if (success == false) {
    Debug.WriteLine(ssh.LastErrorText);
    return;
}

success = ssh.ChannelSendString(channelNum,"\n","utf-8");
if (success == false) {
    Debug.WriteLine(ssh.LastErrorText);
    return;
}

//  Read the response up to the root shell prompt.  This will differ on your system.
string myShellPrompt = "root@myserver:~#";
success = ssh.ChannelReceiveUntilMatch(channelNum,myShellPrompt,"utf-8",caseSensitive);
if (success == false) {
    Debug.WriteLine(ssh.LastErrorText);
    return;
}

//  Retrieving the text also clears the receive buffer, which matters: if the prompt were left
//  buffered, the next receive would match it immediately.
cmdOutput = ssh.GetReceivedText(channelNum,"utf-8");
if (ssh.LastMethodSuccess == false) {
    Debug.WriteLine(ssh.LastErrorText);
    return;
}

Debug.WriteLine(cmdOutput);

//  Now run a command as root.
success = ssh.ChannelSendString(channelNum,"ls\n","utf-8");
if (success == false) {
    Debug.WriteLine(ssh.LastErrorText);
    return;
}

success = ssh.ChannelReceiveUntilMatch(channelNum,myShellPrompt,"utf-8",caseSensitive);
if (success == false) {
    Debug.WriteLine(ssh.LastErrorText);
    return;
}

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

Debug.WriteLine(cmdOutput);

//  Additional commands follow the same pattern: send the command, read to the next prompt, then
//  fetch and clear the receive buffer.

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

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

ssh.Disconnect();