Walker News » Remote Access

How To Turn Off Or Disable The Citrix Beep Sound?

Walker — Tue, 30 Jun 2009 16:05:28 +0000

I am mad and frustrated by the annoying high pitch beeping tone when using application via Citrix XenApp (an application delivering system).

The Citrix beeping whenever I hit unnecessary keystrokes in the Vi editor or Linux command prompt through Putty remote access program!

While listening to Beethoven’s Piano Concerto No.5 (I find classical best when I am seriously working on something), that flipping beep tone just too bad and makes everyone seated near to me feels uneasy :-(

Because I was rushing on a remote Linux machine, via Putty program delivered by Citrix XenApp Web Plugin, so I just turn off the Dell Latitude speaker that no doubt effectively solved it in no time.

Obviously, that fix is not good at all and too “costly”, as turning off speaker means no more Beethoven’s classical music playing too :-(.

So, I need a proper trick and thus briefly looking around Windows settings in the hope of fixing it myself. But, none of these works:

1) Turn off the “Windows Sounds” found in Vista SP2 Volume Mixer dialog box.

2) Set the Windows sound theme to “No Sounds” scheme

3) Edit the Launc.ica and set the “ClientAudio=Off”.

I am pissed off and went to ask Google for help. Luckily, locating the solution is quick. Indeed, the Googling is much speedy than trying various Windows settings myself.

Credit goes to Leroy Spencer:

As you can see, the trick is fairly simple and easy to remember. For Windows Vista (or perhaps Windows 7), you need to run an elevated mode of Command Prompt window and execute this command to temporarily turn off or disable Windows beep service (looks like a kernel mode driver):

sc stop beep

If you desperately want to turn it off in a persistent mode, run this command after stopping it:

sc config beep start= disabled

Thus, to re-enable beep service to its original start up mode (in this case, SYSTEM_START), execute

sc config beep start= system

Please take note that you need a space between the equal sign and the option value (valid START option values are boot, system, auto, demand, disabled, delayed-auto).

Thanks Ross Williamson for highlighting this. For more information, type sc config.

To query the Beep driver configuration-related information, execute:

sc qc beep

To query the beep driver running status in Vista SP2, execute

sc query beep

I prefer to keep it running so I won’t miss something else in future. Having said that, I need to execute sc stop beep each time running Citrix XenApp Web Plugin.

How To Use Putty-generated RSA Key To Login Linux OpenSSH Server?

Walker — Sun, 10 May 2009 16:28:04 +0000

In order for Windows users to remotely login Linux servers via SSH protocol, I suggest the Putty freeware (a SSH client for Windows that is also supporting legacy, insecure telnet and rlogin protocol).

For the sake of better security, most system administrators enforce SSH authentication over Public-key cryptography based on RSA algorithm.

(Sounds complicated and high-tech? No worry. You don’t have to know all these scary terms to make this trick works – engineer is applying what the scientists have found).

So, How to use Putty-based RSA public-key with OpenSSH server?

The public-key generated by Puttygen is not compatible with the one generated by OpenSSH.

However, you can manually modify the Putty-based public key before appending it to authorized_keys file:

1) Open Puttygen (Putty Key Generator), click Generate button and move the mouse cursor randomly within the key section/frame to create the key with default settings (e.g. SSH-2 RSA of 1024 bits).

2) When the key generation completes, create a strong passphrase in the text box provided.

3) Then, click save Public Key and Save Private Key button, one after another, to save the pair of key to local hard disk.

4) Transfer the Puttygen-created public key to Linux server (in my test case, it’s RHEL 5.2).

Let’s say this public key is only meant for Walker user account, save that public key in Walker’s $HOME/.ssh directory.

5) Open the Putty public key with Vi editor (any text editor of your choice):

Delete the lines initial with four dash and “Comment”.
Join the remain lines into one, single line.
Initial that single line with ssh-rsa keyword (a space at the end).

Not get it? Take a look at my “silent” screencast:

How To Create Putty-based RSA Public-key For OpenSSH Server?

Walker — Sun, 03 May 2009 11:00:53 +0000

If you want to remote access Linux server via SSH protocol from Windows system, I recommend you to use Putty (a Telnet/SSH freeware for Windows and UNIX; developed by an English man called Simon Tatham).

To strengthen security, don’t ever use plain text password, try to use RSA-based Public-key cryptography for user authentication. The Puttygen (Putty Key Generator; another freeware of Simon) can generate both RSA and DSA-based key pair.

However, the RSA public-key generated by Puttygen is not 100% compatible with OpenSSH server (the dominant SSH server in most Linux distributions).

To make it work, you need to modify the Putty-based RSA public-key before appending it to authorized_keys file.

Steps to generate Putty-based RSA key pair to login Linux OpenSSH server

1) Open Puttygen program and click Generate button to create a 1024-bit, SSH-2 RSA key pair. After clicking the Generate button, move the mouse cursor inside the Key frame repeatedly (Puttygen need these movements to create a “perfect random key pair”).

2) Once the key pair generation complete, think of a “strong” password and enter it twice in the Key Passphrase and Confirm Passphrase text boxes provided in Key frame.

3) Click Save Public-key and Save Private-key buttons to keep these two keys in local hard disk.

4) Transfer the public-key to your Linux home directory (assuming this public-key is made for yourself) and open it with vi editor (any text editor of your choice).

5) The original Putty-based RSA public-key is similar to this:

You need to delete the lines started with “4 dash” and “Comment:” (i.e. first two and the last line).

Next, join all the remaining lines into one, single line.

Then, insert this ssh-rsa keyword (with a trailing space) in front of the single line.

The final, modified Putty-based RSA public-key will looks like this:

6) Now, append the modified Putty-based RSA public key to $HOME/.ssh/authorized_keys file and you’re ready to use Putty to access Linux OpenSSH server with private and public key generated by Puttygen.

How To Fix “Server Refused Our Key” Error That Caused By Putty Generated RSA Public Key?

Walker — Sun, 22 Mar 2009 08:16:40 +0000

The SSH-2 protocol supports few user authentication types, one of which is public-key cryptography.

Other than security benefit, using public-key cryptography in SSH protocol is relatively easier to implement password-less or non-interactive authentication.

For example, a scheduled shell script can use scp (secure copy) to automate file-transfer between hosts seamlessly in background, without user interaction during authentication stage.

With OpenSSH, default SSH client/server software bundled with most Linux distributions, the ssh-keygen program is used to generate a pair of such cryptographic keys.

As for Putty, popular SSH client suite for Windows, there is this Puttygen program to provide similar functions of ssh-keygen.

However, there is incompatibility issue between RSA type of public key generated by ssh-keygen and Puttygen.

Having said that, you can’t install OpenSSH-generated private key in Putty program. Otherwise, the public-key authentication failed with message that says “Unable to use key file “E:\id_rsa” (OpenSSH SSH-2 private key)”.

Similarly, it’s not possible to install a Puttygen-generated public-key directly into OpenSSH authorized_keys file. If you do so, Putty fails with “Server refused our key” error message during authentication.

So, how to install a Putty-generated RSA type of Public-key in OpenSSH authorized_keys file?

This is the latest “silent” screencast in WalkerNews Channel @ YouTube (alive with background music from AudioSwap):

If you’re on fast and stable connection, please click the HQ button on for watching this screencast in high quality video mode.

As you’ve seen, the trick is to modified a Puttygen-generated public-key to the format of OpenSSH-generated public-key:

1) Edit Putty-generated public-key file with Vi editor,

^{Original RSA type of public-key generated by Puttygen program.}

2) Delete the first two and the last line,

3) Join the remaining lines into one single line, by using the Shift+J command shortcut. Remember to trim space between two line joined by CTRL+J command.

4) Insert ssh-rsa keyword (with one trailing space) in front of the single line.

5) [ OPTIONAL ] Append Login_ID@Host_name keyword (with a initial space) at the end of the single line (replace Login_ID and Host_name with your SSH login ID and host name accordingly).

^{Modified, tweak RSA type of public-key generated by Putty client program, to be installed into OpenSSH authorized_keys file.}

6) Append the modified, tweaked Putty-generated public-key (RSA type) to OpenSSH authorized_keys file.

Now, Putty is able to login OpenSSH server with its own set of public-key and private-key pair:

How To Quit From Telnet Login Prompt Immediately?

Walker — Thu, 19 Mar 2009 14:48:22 +0000

To many of you, this is not an interested post. However, it will not cost much for recording it here as a reference.

Question: You’re accessing Linux command prompt in front of server console or via remote access client (be it a insecure telnet or encrypted SSH connection).

Then, from that Linux command prompt, you make a telnet connection to other telnet server (be it a Unix/Linux-based or the Windows Telnet server).

While at telnet login prompt, you find out that is not the right telnet server to access and want to quit immediately.

So, how could you exit from the telnet login prompt immediately, without waiting for it to time out or forcibly terminate the telnet client process?

Answer: I find out that the telnet client of either Windows Vista Ultimate or Red Hat Enterprise Linux 4 supports the same “escape” key.

This special key, better known as “escape character” brings up the telnet > command prompt instantly when it’s pressed.

As seen in this following screenshot, the “escape character” is ^]. That’s to say, press CTRL and ] together for the telnet > command prompt and just enter quit command to end the telnet client process properly:

With this “proper” way, there is no need to wait for time out, simply close Putty window, or execute kill -9 command from another session.

How To Allow Root Login To Telnet Server In Linux?

Walker — Tue, 17 Mar 2009 17:15:23 +0000

Although remote access via telnet protocol is highly discouraged by most system administrators, there are still fans and old boys who are reluctant to change.

Interestingly, these people (who I’ve been dealing with) are all Windows users, i.e. they either use Windows at most of the time or they never have their hands on Linux at all.
So, I guess these people will only abandon telnet client when Microsoft start to bundle Secure Shell (SSH) clients with Windows OS :-(

Now back to topic, if you really want to put the Linux host at risk by allowing telnet protocol, here is the way to enable telnet server in Red Hat Enterprise Linux system (in case you’re asking).

Next, we look at How to enable root account telnet to Red Hat Linux system, if you have nothing to worry about system security (because you’re sysadmin, not security administrator :-)

Telnet client transmit account password in plain text format over (vulnerable) network. Thus, by default, Red Hat Linux (and most Linux distributions, I believe) disables telnet daemon and disallow root user to login directly via telnet protocol.

When you telnet to RHEL server with root ID, it will always rejects with message saying “Login incorrect”, no matter how many times you’ve entered the correct root password:

To overcome this “problem”, simply open /etc/pam.d/remote and remark this following line, where the PAM module pam_securetty.so disallows root user login remotely via telnet and the alike (except SSH).

Original /etc/pam.d/remote with this line:

auth       required   pam_securetty.so

Tweaked /etc/pam.d/remote that remark (comment out) pam_securetty.so:

# auth       required   pam_securetty.so

This guide has been tested successfully on system running RHEL4. It should be valid for use in other Linux distributions that implement Linux-PAM modules (Pluggable Authentication Modules for Linux).

How To Fix Telnet Rejection Error of Name or Service Not Known: Illegal Seek

Walker — Wed, 19 Nov 2008 17:16:08 +0000

We all know that telnet is a good remote access protocol in the old days. Now, we prefer SSH protocol because SSH is a secure protocol, i.e. it’s not easy to hack.

However, for some reasons, telnet server still installed for some (Microsoft Windows) users who desperately need remote access facility. (Maybe telnet server will go into history when Windows start to bundle Putty or its own SSH client).

So, this is what happen here, that we have to install and enable the insecure telnet server on all Red Hat Enterprise Linux servers, for obvious reason.

Problem happen today when one user reported that he cannot telnet to the server, with an rejection error message that said “GetAddrInfo: : Success. Name or service not known: Illegal seek” (as seen in the following screenshot taken when I telnet to localhost in a SSH session):

How to fix this so-called “Name or service not known: Illegal seek” error (replied by the telnet daemon)?

Well, I guess this has something to do with DNS resolution. It was working fine until we changed the Linux hostname on yesterday. The hostname is not registered to DNS servers that defined in /etc/resolv.conf file and there is no hostname-to-IP mapping in /etc/hosts file as well.

So, to try out the possible solution, I add in hostname-to-IP mapping in /etc/hosts file, and it works:

192.168.20.21      WalkerNews      WalkerNews.net

[ assuming the hostname is WalkerNews and its IP address is 192.168.20.21]

I am not sure (because I haven’t tried) the problem will be fixed, if I remove the hostname-IP mapping in /etc/hosts and register the hostname-IP to DNS servers that defined in /etc/resolv.conf file. (I bet this will work, too).