---
name: "pdkill"
section: "2freebsd"
platform: "linux"
package: "freebsd-manpages"
version: "12.2-2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/pdfork/2freebsd"
---

# pdkill(2freebsd)

System calls to manage process descriptors

Part of [pdfork(2freebsd)](/pdfork/2freebsd.md).

## NAME

**pdfork**, **pdgetpid**, **pdkill** – System calls to manage process descriptors

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

**#include \<sys/procdesc.h\>**

*pid\_t*\

**pdfork**(*int \*fdp*, *int flags*);

*int*\

**pdgetpid**(*int fd*, *pid\_t \*pidp*);

*int*\

**pdkill**(*int fd*, *int signum*);

## DESCRIPTION

Process descriptors are special file descriptors that represent processes, and are created using **pdfork**(), a variant of [fork(2)](/fork/2.md), which, if successful, returns a process descriptor in the integer pointed to by *fdp*. Processes created via **pdfork**() will not cause SIGCHLD on termination. **pdfork**() can accept the flags:

- PD\_DAEMON

  Instead of the default terminate-on-close behaviour, allow the process to live until it is explicitly killed with [kill(2)](/kill/2.md).

  This option is not permitted in [capsicum(4)](/capsicum/4.md) capability mode (see [cap\_enter(2)](/cap_enter/2.md)).

- PD\_CLOEXEC

  Set close-on-exec on process descriptor.

**pdgetpid**() queries the process ID (PID) in the process descriptor *fd*.

**pdkill**() is functionally identical to [kill(2)](/kill/2.md), except that it accepts a process descriptor, *fd*, rather than a PID.

The following system calls also have effects specific to process descriptors:

[fstat(2)](/fstat/2.md) queries status of a process descriptor; currently only the *st\_mode*, *st\_birthtime*, *st\_atime*, *st\_ctime* and *st\_mtime* fields are defined. If the owner read, write, and execute bits are set then the process represented by the process descriptor is still alive.

[poll(2)](/poll/2.md) and [select(2)](/select/2.md) allow waiting for process state transitions; currently only POLLHUP is defined, and will be raised when the process dies. Process state transitions can also be monitored using [kqueue(2)](/kqueue/2.md) filter EVFILT\_PROCDESC; currently only NOTE\_EXIT is implemented.

[close(2)](/close/2.md) will close the process descriptor unless PD\_DAEMON is set; if the process is still alive and this is the last reference to the process descriptor, the process will be terminated with the signal SIGKILL.

## RETURN VALUES

**pdfork**() returns a PID, 0 or -1, as [fork(2)](/fork/2.md) does.

**pdgetpid**() and **pdkill**() return 0 on success and -1 on failure.

## ERRORS

These functions may return the same error numbers as their PID-based equivalents (e.g. **pdfork**() may return the same error numbers as [fork(2)](/fork/2.md)), with the following additions:

- \[EINVAL\]

  The signal number given to **pdkill**() is invalid.

- \[ENOTCAPABLE\]

  The process descriptor being operated on has insufficient rights (e.g. CAP\_PDKILL for **pdkill**()).

## SEE ALSO

[close(2)](/close/2.md), [fork(2)](/fork/2.md), [fstat(2)](/fstat/2.md), [kill(2)](/kill/2.md), [poll(2)](/poll/2.md), [kqueue(2)](/kqueue/2.md), [wait4(2)](/wait4/2.md), [capsicum(4)](/capsicum/4.md), [procdesc(4)](/procdesc/4.md)

## HISTORY

The **pdfork**(), **pdgetpid**(), and **pdkill**() system calls first appeared in FreeBSD 9.0.

Support for process descriptors mode was developed as part of the TrustedBSD Project.

## AUTHORS

These functions and the capability facility were created by Robert N. M. Watson ⟨*rwatson@FreeBSD.org*⟩ and Jonathan Anderson ⟨*jonathan@FreeBSD.org*⟩ at the University of Cambridge Computer Laboratory with support from a grant from Google, Inc.