03-D.6: Permission Issues and How to Troubleshoot

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EXAM OBJECTIVES COVERED
4.3 Given a scenario, analyze and troubleshoot user issues.

Troubleshooting

Troubleshooting is a form of problem solving often applied to repair failed products or processes on a machine or a system. It is a logical, systematic search for the source of a problem in order to solve it and make the product or process operational again. Troubleshooting is needed to identify the symptoms. Determining the most likely cause is a process of elimination—eliminating potential causes of a problem. Finally, troubleshooting requires confirmation that the solution restores the product or process to its working state. In general, troubleshooting is the identification or diagnosis of "trouble" in the management flow of a system caused by a failure of some kind. The problem is initially described as symptoms of malfunction, and troubleshooting is the process of determining and remedying the causes of these symptoms.

There is a very handy cheat sheet, created by Setyh Kenlon, that is available by following this link. It is a pdf file which you can download and keep handy as you hone your Linux skills.

There are numerous web sites and "cheat sheets" that you can find to help you resolve problems with permissions. Although, in the previous several pages you have been introduced to the simple concepts...there is so much more that you will learn as you gain experience.

There are some basic things to remember about permissions:

Always look at the existing permissions - and make sure that the reported issue would agree with these permissions. If need be you can used chmod to alter the permissions.
Look to see if the SUID or SGID bit is set. Is it a lowercase or uppercase - that will tell you whether the underlying permission is set.
Is the sticky bit set? This will change certain user's ability to remove the file.
Check to see if an ACL is enabled on the file, since these controls do not show up in the normal permissions.
REMEMBER -Directory Permissions: Read, write and execute permissions are set for directories as well as files. Read permission means that the user may see the contents of a directory (e.g. use the ls command for this directory.) Write permission means that a user may create files in the directory. Execute permission means that the user may enter the directory (i.e. make it his current directory.)
Look at the parent directory as it may have some permission set that controls the files and sub-directories.

As you gain experience this will get easier.

Troubleshooting the setfacl and getfacl commands can be a bit daunting. This video covers the basics of those commands to help you get started in the proper direction.

Adapted from: "Troubleshooting" by Various Contributors, Wikipedia is licensed under CC BY-SA 4.0