Chow Help Pages

Welcome. to the the new server for chow.mat.jhu.edu! These pages provide brief help about the main Linux system in the mathematics department at Johns Hopkins University.

The new server's operating system is Red Hat Enterprise Linux 6.2. There are many major or minor things that are different from the previous server. The general help pages are under construction. We outline some important things here. Feedback about these pages is very welcome. Please send comments to jkong@math.jhu.edu.

Remote SSH login.

1. If you use SSH to connect to chow and you are not using the JH network (meaning you are off-campus and are NOT using the JH VPN), you must specify port 122 for SSH. This is a requirement from Network Security. On campus and via the VPN, both port 122 and the standard port 22 will work. If you use one setting for laptop, tablet, etc, use port 122 which always works.

• Example. Use SSH on a Linux/Unix/Mac OS command line: ssh -p 122 chow.mat.jhu.edu
• Example. Set up SSH connection on Windows programs like Putty: Delete the old saved session for chow. Create a new session for server chow.mat.jhu.edu and input 122 for the port (default is 22). Save the new session.
• Example. Use SFTP program like WinSCP: Same as above. You must specify port 122 for SFTP connection to chow.

2. SSH warning. The first time you use ssh to connect to chow after the migration (from any machine), you might get a wanring like below:

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 
@       WARNING: POSSIBLE DNS SPOOFING DETECTED!          @ 
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 
The RSA host key for chow.mat.jhu.edu has changed, 
and the key for the corresponding IP address 128.220.229.17 
is unchanged. This could either mean that 
DNS SPOOFING is happening or the IP address for the host 
and its host key have changed at the same time. 
Offending key for IP in /Users/username/.ssh/known_hosts:38 
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 
@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @ 
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY! 
Someone could be eavesdropping on you right now (man-in-the-middle attack)! 
It is also possible that a host key has just been changed. 
The fingerprint for the RSA key sent by the remote host is 
f2:52:e0:57:72:a6:7c:41:bd:52:9b:6d:fe:68:ef:8b. 
Please contact your system administrator. 
Add correct host key in /Users/username/.ssh/known_hosts to get rid of this message. 
Offending RSA key in /Users/username/.ssh/known_hosts:52 
RSA host key for chow.mat.jhu.edu has changed and you have requested strict checking. 
Host key verification failed.

In this case, do one of the following:

• Remove the cached SSH server fingerprint from your local known_hosts file. 
  In Linux, this is probably at ~/.ssh/know_hosts. 
  In Mac OS, this is probably at /Users/your_account/.ssh/known_hosts. 
  For Windows programs (Putty, OpenSSH, etc) it depends on the program. Delete the save session and create a new one will probably be the easy way.

• Run the following 2 commands from a local system prompt (applies to Linux, UNIX, and MacOS): 
  
  $ ssh-keygen -R chow.mat.jhu.edu 
  $ ssh-keygen -R 128.220.2.97 
  

Mail

1. All email messages have been migrated to the new server. Your procmail and/or mail forwarding options were migrated as well.

2. Local program such as Pine (alias for Alpine) and Evolution work as usual (if you use Evolution, your mail data will be migrated to the new version the first time you use it).

3. Mail programs for IMAP/POP3 will work as usual. If you encounter problem getting new email from your mail program, you can delete and re-create the account on your mail program. Here is the configuration for mail client:

• Choose IMAP or POP3
• Incoming mail server: chow.mat.jhu.edu (use your chow username and password)
• Outgoing (SMTP) mail server: smtp.johnshopkins.edu (use your JHED username and password)
   
• SSL must be enabled for both incoming and SMTP mail servers. Do this before taking the account online.
• The port for SSL enabled IMAP is 993. The port for SSL enabled POP3 is 995. Most mail programs automatically change to that once you enable SSL. But for some programs you need to manually input the correct port number.
• The default root folder for IMAP is your home directory. So for example if you set your IMAP root folder as ~/imap/ (the imap subfolder in your home directory), you should specify it in Advanced settings. Use path imap (do not use absolute path like /home/your_account/imap or ~/imap).
• If you create a new IMAP account, you might need to re-subscribe your imap folders.
• If you use POP3 and want to keep a copy on the server, enable that in Advanced settings before taking the account online.

X-Window Connection

1. If you log into the graphical destkop environment, please note that the environment is completely new and was rewritten. It was not possible to migrate the old desktop configuration to the new server due to the many differences between the server software

2. There are two desktop themes. Gnome and KDE. If you log in Gnome and do not see the menu bar on top, instead you see menu bar on bottom (or worse, no menu at all), then you have some old desktop configurations that are not compatible with the new server. The easy way to get to the new menu to work is to rename the following directories (via SSH session), then log in X-window again. Or contact jkong@math.jhu.edu.

        mv .gnome .gnome.old
        mv .gnome2 .gnome2.old

3. If you have a Linux terminal in your office, the X-connection will works as usual.

4. Here are some quick tips about X-connection to chow:

• Program shortcut icons. In Gnome desktop, click Applications. In KDE desktop, click the start button on left bottom corner, then click Applications. Once you find the application you want, you can right click it and create a shortcut on either desktop on the panel.
• Browser: The default browser is Firefox. In Gnome, there is an icon on the top menu. In KDE, create a shortcut as mentioned above.
• Bookmarks: To import bookmark from Mozilla (from your profile in old server), copy the file bookmarks.html from ~/mozilla/your_account_name/some_long_numbers/  to your home directory. Then in Firefox, click Bookmarks -> Show all Bookmarks. Then click Import and Bakcup -> Import bookmarks from file. Browse to the bookmarks.html in your home directory and click OK.
• Terminal default directory: In Gnome, If you right click "Open in terminal" from desktop, the terminal will open but the directory will be ~/Desktop. (Type cd to go to your home directory.) If you open Terminal from Applications -> System Tools -> Terminal. It will open with your home directory. The easy ways is to create a shortcut of Terminal on your desktop.
• Terminal size and fonts: In Gnome, open a terminal and choose Edit -> Profile Preferences. Uncheck "Use the system fixed width font". Then you can choose font and its size. Click "Close" to save the setting. In KDE, open Console, click Tools -> Edit Profiles. Choose the default profile, from there you can choose the background color and font size, and save the setting.
• X-11 forwarding for SSH: once ssh in chow, type the command: xhost + and press return.

5. Because of  the new operating system. The previously X-Windows program (X-win32) does not work well. At this time we use the program Xming for Windows X-connection to chow. To use Xming, double click the "Chow" icon on the desktop. Once you finish your X-session, after log out from chow and Xming comes back with the login screen, right click the Xming icon on taskbar and choose Close to quit the program.

Math Software

Mathematica (version 9.0), Matlab (version R2012b) and Maple (version 16) have been installed.