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:
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.
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, please connect to the VPN and review the Glue overview documentation on the Linux Support Home webpage.
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.
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.
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:
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.
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.
Your Glue or GRACE account uses your UM Directory passphrase. If you need to change your passphrase, see Passphrase Management.
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.
To check if you are over quota:
If you are still 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).
To delete files in your Pub directory:
To delete files in your Home directory:
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.
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:
| .environment | for modifying environmental variables and conditions |
| .path | for modifying the search path used when executing commands |
| .aliases | for setting user command aliases |
| .cshrc.mine | for setting other user shell variables not mentioned above (do not edit .cshrc) |
| .startup.X | for setting startup commands in X-Windows connections |
| .startup.tty | for setting startup commands in text-only connections |
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.
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.
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.
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