Unshares

Unshares refers to the capability in Linux to disassociate a process from one or more namespaces, thereby creating an isolated view of system resources. The operation can be performed by the unshare system call (unshare(2)) or by the user-space command unshare (unshare(1)). By selectively unsharing namespaces, a process can run with a private mount table, hostname, IPC resources, network stack, process ID space, or user and group mappings.

Namespaces are the core isolation primitives in Linux. The mount namespace controls the set of mounted file systems visible to the process. The UTS namespace provides separate hostname and domain name. The IPC namespace isolates interprocess communication resources. The network namespace gives the process its own network stack and interfaces. The PID namespace provides a separate set of process IDs, such that processes in the new namespace may have their own initial PID, typically 1. The user namespace maps user and group IDs, enabling different privilege levels inside the namespace.

Usage and role: Unsharing is a core primitive in containerization and sandboxing, allowing running programs with a private view of system resources without starting a full container. The unshare command can start a program with specified namespaces unshared from the parent, while other tools such as nsenter can attach to existing namespaces. In practice, unsharing can be combined with other isolation mechanisms to create controlled environments for testing, security research, or lightweight isolation.

Privileges and limitations: Creating new namespaces or unsharing certain namespaces typically requires appropriate privileges in the current user namespace (for example, CAP_SYS_ADMIN). Consequently, not all unshares are allowed in all environments without specific permissions. See also Linux namespaces, nsenter, and containerization concepts.