Red Hat Linux 7 Unleashed

By William Ball

• Table of Contents
  • Copyright
  • About the Lead Authors
  • About the Contributing Authors
  • Acknowledgments
  • Tell Us What You Think!
  • Introduction
  • I. Red Hat Linux Installation and User Services
  • Chapter 1. Introduction to Red Hat Linux
  • Chapter 2. Installation of Your Red Hat System
  • Chapter 3. LILO and Other Boot Managers
  • Chapter 4. Configuring the X Window System, Version 11
  • Chapter 5. Window Managers
  • Chapter 6. Connecting to the Internet
  • Chapter 7. IRC, ICQ, and Chat Clients
  • Chapter 8. Using Multimedia and Graphics Clients
  • II. Configuring Services
  • Chapter 9. System Startup and Shutdown
  • Chapter 10. SMTP and Protocols
  • Chapter 11. FTP
  • Chapter 12. Apache Server
  • Chapter 13. Internet News
  • Chapter 14. Domain Name Service and Dynamic Host Configuration Protocol
  • Chapter 15. NIS: Network Information Service
    • Understanding NIS
    • Installing the Software
    • Configuring a Master NIS Server
    • Configuring a NIS Client
    • Configuring a NIS Secondary Server
    • Using NISisms in Your /etc/passwd File
    • Using Netgroups
    • Some Troubleshooting Tips
    • Summary
  • Chapter 16. NFS: Network Filesystem
  • Chapter 17. Samba
  • III. System Administration and Management
  • Chapter 18. Linux Filesystems, Disks, and Other Devices
  • Chapter 19. Printing with Linux
  • Chapter 20. TCP/IP Network Management
  • Chapter 21. Linux System Administration
  • Chapter 22. Backup and Restore
  • Chapter 23. System Security
  • IV. Red Hat Development and Productivity
  • Chapter 24. Linux C/C++ Programming Tools
  • Chapter 25. Shell Scripting
  • Chapter 26. Automating Tasks
  • Chapter 27. Configuring and Building Kernels
  • Chapter 28. Emulators, Tools, and Window Clients
  • V. Appendixes
  • A. The Linux Documentation Project
  • B. Top Linux Commands and Utilities
  • C. The GNU General Public License
  • D. Red Hat Linux RPM Package Listings

Using NISisms in Your /etc/passwd File

The most popular use of NIS is to keep a global user database so that it is possible to grant access to any machine at your site to any user. Under Red Hat Linux, this behavior is implicit for all NIS clients.

Sometimes, however, you do not want everyone accessing certain systems, such as those used by personnel. You can fix this access by using the special token + in your /etc/passwd file. By default, NIS clients have the line +:::::: at the end of their /etc/passwd file, thereby allowing everyone in NIS to log in to the system. To arrange that the host remains a NIS client but does not grant everyone permission, change the line to read +::::::/bin/false. This will allow only people with actual entries in the /etc/passwd file for that host (for example, root) to log in.

To allow a specific person to log in to a host, you can add a line to the /etc/passwd file granting this access. The format of the line is + username :::::: where username is the login of the user you want to grant access to. NIS will automatically grab the user's passwd entry from the NIS server and use the correct information for determining the user information (for example, UID, GID, GECOS, and so on). You can override particular fields by inserting the new value in the + username :::::: entry. For example, if the user sshah uses /usr/local/bin/tcsh as his shell but the host he needs to log in to keeps it in /bin/tcsh, you can set his /etc/passwd entry to +sshah::::::/bin/tcsh.

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