File permission on Linux

TL; DR

Log in with the same user with whom you did all the described actions.

Run the umask Command to find out your user's default permissions. The command will return you an octal-based number, type 0002 (ignore the first 0, because, like the 0x that precedes every hexadecimal-based number, the first 0 is irrelevant).

If the files you modified are not directories, then subtract the value obtained with the command umask of 666, and use the resulting value in a new command chmod to be executed on the files. Example:

$ umask
Resultado: "0002"
666 - 002 = 664

$ chmod 664 NOME_DO_ARQUIVO

But if the modified files are directories, replace the 666 in the calculations above with 777.

Explanation of what happened over there

Permissions on a Unix / Linux system are defined by the following character sequence:

_rwxrwxrwx 1 dono:grupo

The _ in the beginning you can ignore for your problem (is a special permissions flag, which can classify the file with special permissions of file, directory or no special permission )

Then there are 3 sets of rwx (where r represents read permission, w write permission, and x execution). The first set displays the permissions of the user who owns the file (who created the file), the second set is the permissions of the group to which the file belongs (a group can contain more than one user), and the last set of permissions are the permissions for all other users of the system.

dono:grupo represents which user and group the file belongs to.

Then a file with the following permissions _rw_rw_r_ can be read and written by the file owner and the users belonging to the file group. Other users can only read the file.

To change the permissions of a file you use the command chmod followed by 3 numbers representing, in order, the permissions for owner, Group, Other Users. The numbers can be:

• 4 for reading
• 2 for writing
• 1 for execution
• any sum of the previous ones (e.g. 4 + 2 = 6, represents read + write permission)

That's why your command chmod 777 released everything you wanted to do in the file, because 7 = 6 + 2 + 1, that is, permission to read, write and execute pro owner, group and others system users.

So now you know how to set the permission of files or directories the way you want, but what about

And now I would like to return to the default linux system files.

For this you can use the command umask. It returns which not permissions should be set on all files and directories created by the current user on the system. For default (non-root) users, the default value is 0002 (ignore the first 0 which only indicates that the number is on octal basis), while for root users the default is 0022.

Then to set the permissions of a normal file, subtract the value returned by umask from 666 and use this new value in the chmod command.

And to set directory permissions, subtract umask from 777.

References

Https://www.linux.com/learn/tutorials/309527-understanding-linux-file-permissions http://www.tutonics.com/2012/12/linux-file-permissions-chmod-umask.html