The chmod Command

How to use the versatile command chmod.
Power chmod

Chmod also provides a few command line options to simplify administrative tasks. For changing file permissions in directory trees use -R.

$ chmod -R g-w test_dir

This would remove write permission for group for all of the files in and below test_dir.

In order to control the output of messages from chmod use -c, -v and -f:

$ chmod -v 700 test_file
mode of test_file changed to 0700 (rwx------)

This option caused chmod to display how the permissions of test_file were set. The -c option causes chmod to display messages only when files are changed, and the -f option suppresses messages about files that can't be changed.

Chmod also provides a --version option to display the version and --help to see a short help message.


File permissions are an integral part of Linux. The same concepts also apply to other operating system objects such as semaphores, shared memory, and NIS+. This tutorial provides you with some of the basic knowledge necessary to protect your data and have more fun with your Linux system, and provides you with mental building blocks for learning more about Linux.

Eric Goebelbecker ( is a systems analyst for Reuters America, Inc. He supports clients (mostly financial institutions) who use market data retrieval and manipulation APIs in trading rooms and back office operations. In his spare time (about 15 minutes a week...), he reads about philosophy and hacks around with Linux.



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Re: Take Command: The chmod Command

Anonymous's picture

is it possible to explain the meanings and values of those chmod numbers. e.g chmod 750