Unix-like operating systems share a family of conventions for processes, files, users and small composable tools. Linux, the BSD systems and macOS inherit many of these ideas.

Hierarchical filesystem

The filesystem has a single root written

/

with paths such as

/etc
/home
/usr/bin

Devices and kernel interfaces may also appear through file-like objects, making many system resources accessible through familiar read and write operations.

Users and permissions

Processes run under user and group identities. File permissions can grant read, write and execute capabilities separately to owners, groups and others.

A privileged administrative account can perform operations unavailable to ordinary users.

Processes

Programs run as processes with identifiers, parent-child relationships, environment variables, open files and exit statuses.

Signals provide a standard mechanism for requesting actions such as termination or interruption.

Composable tools

Unix culture favors small programs that perform focused tasks and can be connected through standard input and output.

This design becomes especially visible in the shell, where redirection and pipelines let independent programs form larger workflows without needing to know one another's internal implementation.