Pidfd

Linux / 23 Sep 2026 / 4 min read

pidfd_getfd Duplicates a Target Descriptor into the Calling Process

pidfd_getfd Duplicates a Target Descriptor into the Calling Process pidfd_getfd() can place a duplicate of another process’s open file descriptor into the caller’s descriptor table. The returned descriptor is local to the caller, but it refers to the same open file description as the selected descriptor in the target process. That distinction matters. This operation does not reopen a pathname, reconstruct a socket, or create an independent file position. It duplicates an existing kernel reference across a process boundary.

Linux pidfd

Linux / 20 Sep 2026 / 5 min read

pidfd_getfd Duplicates a Live File Descriptor Across Processes

A process can acquire a usable duplicate of a file descriptor that is already open in another process without asking that process to send it over a UNIX domain socket. Linux pidfd_getfd() performs that transfer through a PID file descriptor, subject to a ptrace access check. The returned descriptor is new in the caller, but the kernel object behind it is not independent. It refers to the same open file description as the target descriptor. That distinction controls offset sharing, file status flags, and operations on the underlying object.

Linux pidfd

Linux / 19 Sep 2026 / 5 min read

PID File Descriptors Give Linux a Stable Handle for Process Lifecycle Events

A numeric PID can name one process now and a different process later. Linux PID file descriptors change that boundary: a pidfd is a file descriptor that refers to a task, so process operations can remain attached to the intended kernel object instead of repeating a lookup by numeric PID. This distinction matters in supervisors, service managers, container runtimes, and other software that observes process lifecycles. A PID is useful for naming, but it is not a durable capability. A pidfd can participate in file-descriptor APIs and can be retained across the interval between identifying a process and acting on it.

Linux Processes

Cybersecurity / 18 Sep 2026 / 6 min read

Pidfd Process References Separate Identity from Numeric PIDs

A supervisor records a worker PID, performs unrelated work, then sends a signal to that number. If the original worker exited and the kernel reused its numeric PID, a later operation can address a different process. The number identifies an entry in a PID namespace at a moment in time; it is not, by itself, a durable process handle. Linux pidfds add a file-descriptor representation of process identity. A pidfd obtained for a process continues to refer to that process rather than being retargeted when its numeric PID is recycled. This changes the identity boundary for supervision, but it does not grant broad authority over the referenced process.

Cybersecurity Linux Security

Cybersecurity / 17 Sep 2026 / 5 min read

Pidfds Turn Process Identity Into a Stable Kernel Reference

A supervisor records PID 1842 for a worker, waits for an asynchronous event, then sends a signal. Between those operations the worker can exit, be reaped, and its numeric PID can later identify another process. The number still looks valid, but the identity it denotes has changed. Linux pidfds move this class of process control away from repeated numeric lookup. A PID file descriptor refers to a particular process, giving userspace a kernel-held reference that can be passed to interfaces such as pidfd_send_signal(), polling APIs, and, under additional permission checks, pidfd_getfd().

Cybersecurity Linux Security