Explain Linux Command Execution, Filesystems, and Isolation

Walk through the operating-system mechanisms behind common Linux commands and isolation choices. Keep the explanation concrete: identify user-space work, system calls, kernel objects, permissions, and failure paths instead of treating each command as a black box.

Clarifying Questions to Ask

• Which shell and executable-search rules should be assumed?
• Should the discussion focus on Linux specifically or portable Unix behavior?
• Are namespaces and cgroups in scope for containers?
• How deep should packet-routing and device-driver details go?

Part 1: From Shell Input to a Running Command

Explain what happens after a user enters an external command. Contrast that path with a shell builtin such as cd. Then explain at a high level how ls, pwd, ip, and legacy interface-inspection tools obtain their results.

What This Part Should Cover

• Parsing, expansion, path lookup, process creation, exec, waiting, and exit status
• Why a child process cannot change its parent shell's working directory
• Directory enumeration and metadata system calls
• Working-directory state and kernel networking interfaces

Part 2: Files, Directories, Permissions, and procfs

Explain how a process opens a path, how directories differ from regular files, how user and group permission checks are applied, what major top-level filesystem areas represent, and why /proc is not an ordinary disk directory.

What This Part Should Cover

• Path traversal through directory entries to inode-like objects
• File descriptors and the open-file-description layer
• Directory execute versus read permission and effective credentials
• Virtual filesystems and process/kernel views exposed through /proc

Part 3: Containers Versus Virtual Machines

Compare containers and virtual machines, including isolation boundary, kernel sharing, startup and resource overhead, operational trade-offs, and cases where each is a better fit.

What This Part Should Cover

• Namespaces, cgroups, capabilities, and shared-kernel risk
• Hypervisor and guest-kernel isolation
• Image, portability, density, and boot-time trade-offs
• A workload-driven choice rather than a universal preference