What is Glue?

Glue is a managed enterprise Linux environment developed and used at the University of Maryland.  It is not an OS but a centralized way to manage multiple systems, so they all look similar.  In other words, it’s a configuration management tool.  Like Microsoft Endpoint Configuration Management (MECM) or JAMF for Apple device configuration management, DIT’s Glue provides configuration management for Red Hat Enterprise Linux (RHEL).  Glue isn’t a singular commercial off-the-shelf (COTS) product but comprises commercial and open-source software, scripts, account management, and processes.  This set of installation elements provides several advantages:

• Consistency: As far as possible, every Glued machine looks like every other. You can walk across campus, log in to a Glued machine in another department, and it'll look just like the machine on your desk.
• Centralized Administration: The Glue environment makes it possible for a comparatively small staff in the Division of IT (DIT) to provide a managed Linux operating system, publish and install patches, license Linux, collect reports, maintain common applications, and so forth.
• Distributed Control: While Glue is centrally administered, individual campus departmental system administrators maintain control over their systems, including root access.
• Security: Glue heavily uses Kerberos and SSL  for security, and its centralized administration means that patches can quickly be evaluated and installed everywhere.

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How do I get a Glue account?

Now that you know what Glue is, you may want to use some of the resources noted below.  Your Glue is automatically provisioned when you become a member of the UMD community. You will get an email about the activation. Affiliates can have access to Glue via the sponsoring process.

For additional information about Glue, please connect to the VPN and review the Glue overview documentation on the Linux Support Home webpage.

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How do I get a Glue Root Account?

Root access is managed centrally for convenience and security. Each user with root access has a password, which is shared across any machine they have. Root passwords are stored in the Kerberos database, just like standard accounts.  A root instance alone does not grant elevated privileges on any host, as individual machines must be configured to allow that instance to be used. Root permissions on individual hosts are handled by modifying Hiera configuration to include a user, Glue Unix group, or netgroup. Hiera also allows access control per node or a set of hosts depending on its inclusion in department or cluster configuration. For additional information about Glue Root Account, connect to the VPN and review the Glue overview documentation on the Linux Support Home webpage.

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How do I get access to GRACE?

Glue accounts are how the GRACE clusters are accessed. The GRACE (Glue Research and Academic Computing Environment) cluster has been established for instructional and research usage of the faculty, staff, and students of the University of Maryland College Park. It is a cluster of Linux servers in the Glue environment.

To access the GRACE cluster, you must first have a Glue account. Instructors wishing to use the GRACE cluster for their class can request access via UMD Grace Account Request.

For additional information about GRACE, please connect to the VPN and review the documentation on the Linux Support Home webpage.

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Connecting to your Glue or GRACE

To establish remote access to general Glue utility servers or the GRACE cluster, you must make a terminal connection. A terminal program is one way to connect and access your account.  Below are the basic steps to getting started with terminal programs.

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Connecting with terminal applications on Windows PCs and Macs

Connecting to Glue or GRACE with a terminal application that uses SSH (secure shell) is generally more secure. There are many different terminal solutions, with varying features for each OS (Windows, macOS, and Linux). Review available options and select the application with the best features.

Some example terminal programs:

• SSH Terminal
  • Putty for Windows
  • Terminal for macOS
  • Native ssh for Linux

• X11 forwarding
  
  • Xquartz for macOS
  • Xming for Windows
  • Putty for Windows

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Logging in for the first time

Once you've connected with the Glue servers (server name: glue.umd.edu) or GRACE system (server name: grace.umd.edu), use your university credentials to log in.

Remember that Linux is case-sensitive, so you must enter your username in all lowercase and passphrase exactly as you entered it when you selected it. In some environments, you may see a prompt:

TERM = (unknown)

If you do, enter vt100 and press Enter (unless you think your workstation is set up for a different terminal type, you should use that type).
<Next, you will see a prompt that will give the name of the machine you are logged in to, followed by :~:.

Some typical prompts include:

y:~:

z:~:

When we refer to a command prompt throughout this document, we refer to the abovementioned prompts.

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Logging off

To log off (or exit) from Glue or GRACE, type logout at the command prompt and press Enter. Logging off when you finish using the Glue or GRACE systems is important.

You are liable at all times for the activity on your account. The Policy governs all Glue accounts on the Acceptable Use of Information Technology Resources.

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Common procedures

Changing your passphrase

Your Glue or GRACE account uses your UM Directory passphrase. If you need to change your passphrase, see Passphrase Management.

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Troubleshooting your Glue or GRACE account

Glue and GRACE account space is limited. Each customer is assigned a disk quota. This quota is an indicator of the number of files you have created and the limit on space that you can use. If you exceed this amount, you cannot access more space until you have deleted some files.

If you log in to your account and get one of these messages, your account may be over quota: Your disk space is exceeded.

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Resolving quota issues

To check if you are over quota:

1. Log in to your account with a terminal session.
2. At the prompt, enter: quota. This displays how much space you are using. You should clear space in your account if you use over 90% of your quota.

If you are over quota, go to the next section to determine which directories and files are causing problems. You can then delete any unwanted items. Your account has two main directories: pub and home. This section looks at the pub and home directories.

The pub directory stores public files for your website (www.glue.umd.edu/~loginname).

• The home directory stores files or directories you've created.

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Deleting files in Pub

To delete files in your Pub directory:

1. While connected to your account using a terminal program, list the files and directories in your pub directory by typing: cd ../pub then list the files from smallest to largest by typing: du -sk * | sort -n
2. If you see a file or directory you no longer need, remove it by typing: rm filename or rm -rf directory

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Deleting files in Home

To delete files in your Home directory:

• Return to your home directory from the pub directory by typing: cd then list the files in order of smallest to largest by typing: du -sk * | sort -n. To delete files, type the command rm followed by the filename (e.g., rm file.html) then press Enter.

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Editing files

The Division of IT Linux systems has several editors for creating new and editing existing files. The three most popular editors are Pico, Emacs, and Vi.

Pico is the easiest text editor to use. This visual editor displays a command list at the bottom of the screen for performing basic tasks such as justifying text, cutting and pasting text, and spell-checking a file. For more information on the pico editor, refer to Using the Pico Text Editor.

Emacs is a very powerful editor. It allows you to use and customize a very large set of commands. Emacs has environmental modes for basic text editing, editing C program files, and editing Lisp program files. For more information on the emacs editor, refer to Using the Emacs editor.

Vi is an editor that is almost universally available on UNIX-based machines. It is available on all UNIX systems maintained by the Division of Information Technology.

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Changing your Account's environment

When establishing your Glue account, several defaults (preset) configuration files govern various parameters, window size, and placement, and where to look for commands. You can alter these defaults by editing various hidden files (dotfiles) in your home directory:

However, should you want to return to default status again, run the original defaults script program again by typing: /usr/local/scripts/newdefaults at the Linux prompt. This will return your account to its default settings. Previous configuration modifications will be moved to filename-date (filename is the file you modified, and date is the date of the modification). For example, .path-27-11-96 would represent the November 27, 1996 version of .path. It is also important to note that after you enter /usr/local/scripts/newdefaults at the UNIX prompt, the .aliases file and any .mine (.cshrc.mine, logout.mine, etc.) files will not be changed.

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Internet services

SFTP (Secure File Transfer Protocol) is used to transfer files from one computer connected to the Internet to another computer connected to the Internet. SFTP and SCP (Secure CoPy) are available on Glue and GRACE. For more information about using SFTP, refer to Transferring Files with SFTP or SCP.

NOTE: Non-secure connections (telnet, ftp) are not allowed to Glue or GRACE hosts.

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Getting help

One feature of Linux is that system documentation is available online. If you need help with a particular command (e.g., identifying appropriate usage or syntax), enter: 

man command

Using the man command displays the relevant UNIX reference manual pages. Review the manual pages if you are uncertain about features associated with any command.

The apropos command lists all online manual sections that contain instances of given keywords in their title. The format for apropos is:

   apropos keyword

Contact the Service Desk should you need additional assistance.

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Glue v2.0 - Enterprise Managed Linux support

For Linux administrators at the university, you may wish to know how you can leverage Glue to your and your Linux systems' benefits. Please review the following article: Glue v2.0 - Enterprise Managed Linux Support

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