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Asked: 2010-12-17 07:47:18 +0800 CST

Why can the root user edit read-only files, but a regular user with sudo access can't?

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If you try to append to a file with no write permissions (say, the /etc/sudoers file which is is owned by root and has 0440 permissions), if you're the actual root user, this works. However, if you're another user using sudo, you get a permission denied error.

Why is this? It not because of the ownership of the file - it doesn't work with files owned by the normal user either. The real root user seems to have more permissions than are granted with sudo. What's the rationale for this? Is there a way to grant this permission to users using sudo?

unix sudo file-permissions

2 Answers

  1. Best Answer

    Sounds like you're doing something like:

    sudo echo "blah blah blah de blah" >> /etc/protected_file

    This doesn't work because sudo applies to the echo command, which happily runs as root, but the redirect is part of your current shell, which isn't running as root.

    Common solutions are:

    sudo bash -c 'echo "blah blah blah de blah" >> /etc/protected_file'

    and

    echo "blah blah blah de blah" | sudo tee -a /etc/protected_file
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  2. Note: You should be using "visudo" to edit the sudoers file, because it checks the file for syntax errors before letting you commit them, to prevent you from locking yourself out.

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