You would have noticed that some modifications require us to change the file permissions. Most the time it’s a system application which needed to be dropped manually using Root Browser or similar app. If you don’t set permissions properly it can make mod you are using may not work.

Here is nice tutorial to understand Unix file system briefly:http://www.elated.com/articles/understanding-permissions/

Well, Let’s go back to setting file permissions.

You have noticed that mod which requires setting file systems are usually applied by this way.

1. Download file and save it on sdcard

2. Push file to /system/xxx using root manager or similar app.

3. Set permissions to rw-r-r or whatever mentioned.

4. Reboot phone.

Most users gets confused on 3rd step. What is this rw-r-r (or whatever mentioned) and how to apply it to file?

In order to apply file permission to file you need Root Browser/Root Explorer etc app. with root access.

Open Root Explorer, you will see all your files and folders listed. Under every listed file or folder you will notice something written like  rwxr-xr-x (see pic) this are the file permissions for respective file or folder.

Changing the file permissions.

Now let’s see how to change file permissions.

1. For example, long press on data folder, you will see menu looking like following pic.

2. Now select permissions you will see options similar to this.

3.  as you can see in the pic above the permission is set to ‘rwxrwx–x’ (771 according to Table below)

So in order to set the right Permission for a file, after you have copied the file to the relavent folder, all you have to follow is the below steps and also the Table guide below it.

1)Any File Manager app like Root Explorer/Browser,Es-file explorer installed with root access.

2)Find the File which you have copied to the appropriate Folder for which you have to set Permissions with the above installed file manager app.

3) Long press on the file to open a pop up menu as shown in First Picture above.

4)Set Permission accordingly ( been suggested by people for you) using the table guide below as reference.

5) Then reboot your phone for the same (Permission set) to take effect.

Table Guide for reference.

No- Box is Unchecked, Yes- Box Checked

So, for example:

777  is the same as rwxrwxrwx

755  is the same as rwxr-xr-x

666  is the same as rw-rw-rw- and so on.

Sources

http://forum.xda-developers.com/showthread.php?t=1857648

http://www.xda-developers.com/android/brief-primer-on-file-permissions-for-new-users/