The nitty gritty of Unix rights management

Cross-Examination

Article from Issue 177/2015
Author(s):

People applying for IT jobs should brace themselves for the popular interview question about the sticky bit in Unix operating systems. It certainly pays to know.

A frequently asked IT interview question concerns the "sticky bit." I do not personally ask this question when vetting a candidate, because I think anyone who knows the answers is, at best, showing good interview preparation. It does not provide any proof of professional expertise. However, many Silicon Valley companies have the question in their catalog and, as a player in the software industry's major league, you need to know the answer to unnecessary questions.

That's why I picked the topic for the Perl column this month. What is the sticky bit's purpose? Michael Kerrisk's book [2] – as always – helps when it comes to tricky Unix questions. As a hardback, this tome with more than 1,500 pages seems to be designed for bodybuilders, but it is easy to carry around anywhere as an e-book. Those who think they understand the intricacies of programming in Unix will stand back in amazement upon reading this epic book: Even gray-bearded Unix gurus will discover intriguing facts from the depths of this resource, time and time again.

For example, did you know that users on a Unix system can delete a file from a directory even if they do not have any write permissions on the file? Correct: Only write and execute permissions are required for the directory the file is located in, and the file's permissions don't matter at all. Listing 1 creates new directory test in the current directory for demonstration purposes and uses the 0333 octal value to assign permissions of -wx-wx-wx.

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