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Lesson 9

Unix File Ownership Conclusion

Because access to practically every resource on the system is managed through these mechanisms, this knowledge is crucial to your success as a UNIX system administrator. You are now able to:
  1. Describe the central role that files play in the UNIX environment
  2. List the principles of file and directory ownership
  3. Set user and group ownership
  4. Explain how UNIX grants access to files and directories
  5. Set file and directory access permissions

Key terms

In this module, we used the following terms:
  1. access mode: The access mode is the first column of an ls -l listing. The access mode is composed of a file type followed by the user permissions, group permissions, and other permissions.
  2. access permission bits: Access permission bits are a series of 9 bits that describe various file permissions. The first 3 access permission bits describe the read, write, and execute permissions for the file's user. The second 3 bits describe the read, write, and execute permissions for the file's group. The final 3 bits describe the read, write, and execute permissions for others.
  3. group: A group allows an arbitrary set of users to share files. When a user is a member of the file's group, the user will have that file's group permissions.
  4. group permission: Group permissions are the second set of read/write/execute permissions in an access mode. Group permissions apply to users that are members of the file's group.
  5. other permission: Other permissions are the third set of read/write/execute permissions in an access mode. Other permissions apply to everyone besides the file owner and the group members.
  6. owner: The file owner is typically the user who created the file. You can change permissions only on files you own.
  7. Permission type: A permission type grants users a particular type of access. The three basic permission types are r (read), w (write), and x (execute).
  8. save text permission: Setting the save text permission bit (indicated by t) on an executable file is supposed to tell the kernel to leave a program in memory after it terminates. This use is now largely obsolete. The save text permission on a directory means something slightly different. When this permission bit is set on a directory, a user may delete a file only if he or she has write permission (w) for that file, even if he or she has write permission on the directory.
  9. SGID permission: The SGID permission sets a process's group ID on execution.
  10. SUID permission: The SUID permission sets a process of a user ID on execution.
  11. user permission: User permissions are the first set of read/write/execute permissions in an access mode. User permissions apply to the file owner.

Commands


In this module, we discussed the following commands:
Command Purpose
ls Lists file or directory. With no arguments, ls lists the current directory.
chgrp Changes the group of a file.
chown Changes the owner of a file.
umask Sets the default permission for a new file.
chmod Changes the access mode of a file.

FileOwnership AccessPermissions- Quiz

Click the Quiz link below to take a multiple-choice quiz covering what you learned in this module.
File Ownership Access Permissions- Quiz