February 3, 2014

How to Manage File and Folder Permissions in Linux

For many users of Linux, getting used to file permissions and ownership can be a bit of a challenge. It is commonly assumed, to get into this level of usage, the command line is a must. Although there is always far more power and flexibility to be had, running seemingly complicated command isn't alwaysa necessity. With the help of some of the most user-friendly desktop interfaces available, you can get away with little to no command line usage. Even with file permission and ownership.

That's right, much to the surprise of many a new user, managing files and folders can be done from within the file managers. But before we get to the GUI, it's always best to have a solid understanding of what it's doing. So, we'll start with the command line first.

Command line: File permissions

The commands for modifying file permissions and ownership are:

  • chmod – change permissions

  • chown – change ownership.

Neither command is difficult to use. It is important, however, that you understand the only user that can actually modify the permissions or ownership of a file is either the current owner or the root user. So, if you are user Bethany, you cannot make changes to files and folders owned by Jacob without the help of root (or sudo). For example:

A new folder was created on a data partition called /DATA/SHARE. Both users Bethany and Jacob need read and write access to this folder. There are a number of ways this can be done (one of which would be to join the users to a special group – we'll go over managing groups in another post). If Bethany and Jacob are the only users on the system (and you know your network is safe – very important), you can change the permissions of the folder to give them access. One way to do this would be to issue the command:

sudo chmod -R ugo+rw /DATA/SHARE

The breakdown of the above command looks like:

  • sudo – this is used to gain admin rights for the command on any system that makes use of sudo (otherwise you'd have to 'su' to root and run the above command without 'sudo')

  • chmod – the command to modify permissions

  • -R – this modifies the permission of the parent folder and the child objects within

  • ugo+rw – this gives User, Group, and Other read and write access.

As you can probably surmise, this command opens wide the SHARE folder such that anyone on the system can have access to that folder. As I mentioned earlier, a more secure method would be to use groups. But we're just using this for the purpose of demonstration.

The breakdown of permissions looks like this:

  • u – user

  • g – group

  • o – other

The 'other' entry is the dangerous one, as it effectively gives everyone permission for the folder/file. The permissions you can give to a file or folder are:

  • r – read

  • w – write

  • x – execute

Using the -R switch is important. If you have a number of sub-folders and files within the SHARE directory, and you want the permissions to apply from the parent object (the containing folder) to the child objects (the sub-folders and files), you must use the -R (recursive) switch so the same permissions are applied all the way to the deepest folder, contained within the parent.

Command line: File ownership

Changing the ownership of a file or folder is equally as simple. Say Jacob moved a folder for Bethany into the SHARE directory – but Jacob still has ownership. This can be changed with a simple command:

 

sudo chown -R bethany /DATA/SHARE

 

Let's break this down.

  • sudo – admin rights must be used since we are dealing with a folder that belongs to another user

  • chown – the command for changing ownership

  • -R – the recursive switch to make sure all child objects get the same ownership changes

  • bethany – the new owner of the folder

  • /DATA/SHARE – the directory to be modified

Should Bethany send the folder back to Jacob, the ownership would need to again be changed (again, this will be simplified with the use of groups).

GUI: File permissions

I'm going to demonstrate changing file permissions using the Nautilus file manager on an Ubuntu 13.10 system.

Let's say you need to allow everyone to gain read/write permissions to the folder TEST. To do this, within the Nautilus file manager, follow these steps:

  1. Open Nautilus
  2. Navigate to the target file or folder
  3. Right click the file or folder
  4. Select Properties
  5. Click on the Permissions tab
  6. Click on the Access files in the Others section
  7. Select “Create and delete files”
  8. Click Change Permissions for Enclosed Files
  9. In the resulting window, Select Read and Write under Files and Create and delete files under Folders (Figure A)
  10. Click Change
  11. Click Close.

Nautilus file permissions

The trick comes when you need to change the permissions of a folder which does not belong to you. It can be done, but Nautilus must be started with admin access. To do this, follow these steps:

  1. Open up a terminal window

  2. Issue the command sudo -i

  3. Issue the command nautilus

The sudo -i command gives you persistent access to sudo, until you enter the exit command to remove that access. Once Nautilus is open, you can change the permissions of the folder or file as described above – even if you are not the owner of the folder or file.

NOTE: If you're using a distribution that doesn't use sudo, alter the above instructions to:

  1. Open up a terminal window

  2. Issue the command su

  3. Type your root password and hit Enter

  4. Issue the command nautilus.

After you've completed the task, close the Nautilus window and then the terminal window.

GUI: Change ownership

Changing the ownership of a file or folder will most often require the use of admin rights. So for this, you'll need to start Nautilus in the method described above.

For changing ownership of a folder or file through Nautilus, do the following:

  1. In the Nautilus window (opened with admin rights), locate the folder or file in question

  2. Right click the folder (or file)

  3. Click on the Permissions tab

  4. Select the new owner from the Owner drop-down (below)

  5. Click Close.

Nautilus

That's all there is to it. At this point you shouldn't have any problems changing permissions or ownership for a file or folder with either the command line or the GUI. The use of groups will empower you to alter permission and ownership with more power and security – we'll cover that soon. Until then, enjoy modifying your files and folders!