What are the file permissions? (I)

One of the issues that often cause confusion among users of virtually any operating system are the permissions of the folders and files, a property that is used to ensure that specific users or user groups have access to certain files or folders or may make modifications. Whether in Unix, Linux or Mac OS X, any file is subject to some permissions that are checked every time we tried to access it and, if our user has fewer privileges, we may run into that annoying "Access Denied".

If you are an experienced user, probably all you're going to comment it sounds familiar but, in my view, is an issue worth reviewing and, especially, can help all those who are beginning to manage equipment or dare to take their first steps with a GNU / Linux.

What are file permissions? What are they?

Although today the permissions of files and folders we can prove something in everyday life, operating systems like MS-DOS , Windows 95 or Windows 98 lacked this access control files. By tuning a little, we will focus on the scheme usually gives more headaches for users, ie, which has traditionally been in Unix and compatible systems POSIX , such as Linux and Mac OS X.

Permissions define, in a simple and effective access rules in reading (r), write (w) or execute (x) certain files (if they are not enforceable, the execution is not necessary as is the case with the folders or directories). As its name suggests, some read permissions allow us to open a file or folder to "eyeball" your content, but we can not make any changes until we give write permissions (which are what allow us to make changes .)

Permits, owners and user privileges

Unless a user is an administrator of a system (and therefore can handle at will any file or folder), all users are subject to permission rules when working on your computer or server (eg the hosting of our blog). In fact, permits scheme distinguishes between three types of extent from the viewpoint of the user:

• File owner
• Group represented
• Other users of the system

As you can imagine, the owner of the file (or folder) is the user who created the file and, therefore, usually permissions to access and modify it. User groups can understand them as a grouping of permissions and privileges, therefore, define the extent to which user groups can have within a system (administrators, users with certain privileges, etc.) and serve to narrow the options that they can not having to make individual configurations.

Therefore, combining all 3 types of permissions (read, write and execute) to the 3 perspectives of user (owner, group and other users, which is generally known as UGO, User, Group, Others), all files and folders Unix systems, GNU / Linux and Mac OS X computers are subject to strict access control system to ensure the integrity and access only to "authorized personnel".

Illustrating with an example, imagine we have a text file created by user A (belonging to the user group AA) has the following outline permission:

• Owner: reading and writing
• Group: Reading
• Other Users: None

With such a scheme, the landlord may make changes, other users could access group for reading and other non-users could not access it, much less make modificiaciones (except the administrator user who has permissions to do you want).

Permissions and Security

And what have to do the permissions and security 's a good configuration permits our files can not prevent someone with good intentions make changes to our system and, for example, access to more information or put in proper the integrity of our system or one of our applications. Therefore, a good permission management is a key contributing factor to enhance the security of a system.

Now what? After learning a little theoretical foundation of the permissions on files and folders, the next step will give you delve into the notation and symbols normally used (and we can see on many operating systems) and then pass a practical approach and analyze some details to consider, for example, to improve the security of our web server.

Picture: DeviantArt