The nitty gritty of Unix rights management

Bonus Points

Job candidates receive bonus points if they can explain when Unix displays a directory's sticky bit with t and when with T. The hack with the sticky bit covers the bit that actually displays general execution rights to the directory with the final t in rwt. It is no longer possible to say whether rw- or rwx was configured before the sticky bit was turned on. Unix therefore displays rwt if rwx was present and displays rwT if execute permissions are missing – that is, if rw- existed previously.

Those who also know that not just directories, but also files, can take a sticky bit – which, however, controls something completely different – will demonstrate that they have taken their preparation seriously and have studied Kerrisk's book. These candidates are sure to score 100 points and make it to the next round!


  1. Listings for this article:
  2. Kerrisk, Michael. The Linux Programming Interface: A Linux and UNIX System Programming Handbook. No Starch Press, 2010.

The Author

Mike Schilli works as a software engineer in the San Francisco Bay Area. He can be contacted at Mike's homepage can be found at

Buy this article as PDF

Express-Checkout as PDF
Price $2.95
(incl. VAT)

Buy Linux Magazine

Get it on Google Play

US / Canada

Get it on Google Play

UK / Australia

Related content

  • Beginners: File Control

    From the vault:This article first appeared in issue #1 (October 2000). You'll also find this article on our 10-year anniversary Archive DVD included in issue #120 (November 2010).

    With any operating system it is important to ensure that users remain in control of their files and directories and are prevented from tampering with those belonging to other users, or the system. This is what the Linux permissions system is all about, as Jono Bacon explains.

  • Metadata in the Shell

    Armed with the right shell commands, you can quickly identify and evaluate file and directory metadata.

  • Command Line: Access Control

    A sophisticated system of users and permissions precisely controls who has access to what on Linux. At the command line, you can define ownership with the chmod, chgrp, and chown tools.

  • Command Line: File Management

    Do some serious spring cleaning and reorganize your data. The right commands can help you to keep on top of your file and directory management.

  • File Management

    We give you an overview of commands for moving, editing, compressing, and generally manipulating files.

comments powered by Disqus
Subscribe to our Linux Newsletters
Find Linux and Open Source Jobs
Subscribe to our ADMIN Newsletters

Support Our Work

Linux Magazine content is made possible with support from readers like you. Please consider contributing when you’ve found an article to be beneficial.

Learn More