Page 4 - Newsletter_April_2_2025

By design, Linux is a multi-user operating system. In an enterprise system, there would be multiple users ac-
cessing the same system. But if any user could access and modify all files belonging to other users or system
files, this would certainly be a security risk.
This is why UNIX and thus Linux (Linux is a Unix-like system) has built-in security measure in place. This
ensures that a file or directory can be accessed, modified or executed by only desired users.
Which file would be accessed by which user is decided by two factors in Linux:

· File ownership

· File permission

Understanding file ownership and permission is crucial for a Linux user.

File ownership in Linux.

Each file and directory in Linux have three kinds of owners:

User - User is the owner of the file. When you create a file, you become the owner of the file. The ownership
can be changed as well, but we’ll see that later.

Group - Every user is part of a certain group(s). A group consists of several users and this is one way to man-
age users in a multi-user environment. For example, if you have dev team, QA team and sysadmin team ac-
cessing the same system, you should create separate groups for them. This way, you can manage files and se-
curity of the system effectively. It saves time because instead of manually adding permission for each user,
you can simply add them to a group and change the permission for the group. Even if you are the only user of
the system, you’ll still be part of many groups. Distributions like Ubuntu also create a group with name same
as the user’s name.

Other - ‘Other’ can be considered as a big group with all the users on the system. Basically, anyone with ac-
cess to the system belongs to this group.