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Unix groups

From: Unix for Mac OS X Users

Video: Unix groups

In addition to having users on a system, there is also this idea of groups in Unix. A group is a set of users and each user belongs to at least one group, a primary group, and it can belong to any number of other groups as well. Groups are useful for associating a group of users with a file. So, file's permissions can be set to allow group members to access files, directories or commands, while making sure that people who are not members of that group can not. So for example in a large corporation you might have a group called Human Resources, Legal, or Tech-Support and those users would be granted access to certain files and then by adding a user to one of those groups, they would automatically gain access to all of those files and you wouldn't have to manage access user by user or file by file.

Unix groups

In addition to having users on a system, there is also this idea of groups in Unix. A group is a set of users and each user belongs to at least one group, a primary group, and it can belong to any number of other groups as well. Groups are useful for associating a group of users with a file. So, file's permissions can be set to allow group members to access files, directories or commands, while making sure that people who are not members of that group can not. So for example in a large corporation you might have a group called Human Resources, Legal, or Tech-Support and those users would be granted access to certain files and then by adding a user to one of those groups, they would automatically gain access to all of those files and you wouldn't have to manage access user by user or file by file.

However, setting up managing groups really applies to shared servers and falls under Unix system administration more than Unix usage, and on the Mac you really don't need groups that often. You don't really use it in a multi-user environment that much. So groups really don't apply that often either. But even though you probably won't need to use it, I think it's still a good idea for you at least know about the concept because one day you may very well find yourself working on a well-managed server that does use groups effectively and you will want to know who can access which files. So for now, I just want to let you know that you can type groups and you can see the groups that you belong to.

So these are the groups that Apple has us belong to and Apple then makes these users able to do certain things that have certain permissions. As I said, you'll almost never need to worry about which group you're in. Your Mac manages that for you. It puts you in the right groups. If you ought to be an admin, who has the admin privileges, well, then you're in the Admin group. All the other groups that you are part of may depend on what different software you have installed or what different processes you have running, don't worry about that, okay. I just want you to see that you are a part of a group because groups is going to come up when we talk about file and directory ownership, which we're going to do in the next movie.

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This video is part of

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Unix for Mac OS X Users

82 video lessons · 24962 viewers

Kevin Skoglund
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  1. 3m 57s
    1. Introduction
      1m 14s
    2. Using the exercise files
      2m 43s
  2. 32m 2s
    1. What is Unix?
      7m 27s
    2. The terminal application
      4m 23s
    3. Logging in and using the command prompt
      5m 19s
    4. Command structure
      5m 22s
    5. Kernel and shells
      5m 25s
    6. Unix manual pages
      4m 6s
  3. 15m 58s
    1. The working directory
      2m 49s
    2. Listing files and directories
      3m 59s
    3. Moving around the filesystem
      4m 58s
    4. Filesystem organization
      4m 12s
  4. 1h 4m
    1. Naming files
      5m 41s
    2. Creating files
      2m 19s
    3. Unix text editors
      6m 39s
    4. Reading files
      5m 35s
    5. Reading portions of files
      3m 27s
    6. Creating directories
      2m 40s
    7. Moving and renaming files and directories
      8m 32s
    8. Copying files and directories
      3m 7s
    9. Deleting files and directories
      3m 38s
    10. Finder aliases in Unix
      4m 10s
    11. Hard links
      5m 30s
    12. Symbolic links
      6m 36s
    13. Searching for files and directories
      6m 32s
  5. 34m 58s
    1. Who am I?
      4m 3s
    2. Unix groups
      1m 52s
    3. File and directory ownership
      6m 41s
    4. File and directory permissions
      4m 27s
    5. Setting permissions using alpha notation
      6m 49s
    6. Setting permissions using octal notation
      3m 49s
    7. The root user
      1m 57s
    8. sudo and sudoers
      5m 20s
  6. 52m 34s
    1. Command basics
      4m 4s
    2. The PATH variable
      4m 13s
    3. System information commands
      3m 40s
    4. Disk information commands
      6m 8s
    5. Viewing processes
      5m 0s
    6. Monitoring processes
      3m 36s
    7. Stopping processes
      3m 19s
    8. Text file helpers
      6m 50s
    9. Utility programs
      7m 28s
    10. Using the command history
      8m 16s
  7. 20m 39s
    1. Standard input and standard output
      1m 24s
    2. Directing output to a file
      4m 13s
    3. Appending to a file
      2m 44s
    4. Directing input from a file
      5m 28s
    5. Piping output to input
      4m 40s
    6. Suppressing output
      2m 10s
  8. 41m 28s
    1. Profile, login, and resource files
      9m 11s
    2. Setting command aliases
      6m 59s
    3. Setting and exporting environment variables
      4m 54s
    4. Setting the PATH variable
      6m 10s
    5. Configuring history with variables
      6m 17s
    6. Customizing the command prompt
      6m 5s
    7. Logout file
      1m 52s
  9. 1h 25m
    1. grep: Searching for matching expressions
      5m 21s
    2. grep: Multiple files, other input
      4m 28s
    3. grep: Coloring matched text
      2m 57s
    4. Introduction to regular expressions
      3m 22s
    5. Regular expressions: Basic syntax
      3m 19s
    6. Using regular expressions with grep
      5m 20s
    7. tr: Translating characters
      8m 17s
    8. tr: Deleting and squeezing characters
      5m 30s
    9. sed: Stream editor
      7m 45s
    10. sed: Regular expressions and back-references
      7m 8s
    11. cut: Cutting select text portions
      7m 42s
    12. diff: Comparing files
      4m 35s
    13. diff: Alternative formats
      4m 30s
    14. xargs: Passing argument lists to commands
      7m 25s
    15. xargs: Usage examples
      7m 59s
  10. 42m 25s
    1. Finder integration
      4m 45s
    2. Clipboard integration
      5m 5s
    3. Screen capture
      3m 42s
    4. Shut down, reboot, and sleep
      3m 34s
    5. Text to speech
      2m 36s
    6. Spotlight integration: Searching metadata
      3m 41s
    7. Spotlight integration: Metadata attributes
      4m 24s
    8. Using AppleScript
      5m 23s
    9. System configurations: Viewing and setting
      5m 51s
    10. System configurations: Examples
      3m 24s
  11. 1m 26s
    1. Conclusion
      1m 26s

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