pidfd_getfd(2) — Linux manual page


pidfd_getfd(2)             System Calls Manual            pidfd_getfd(2)

NAME         top

       pidfd_getfd - obtain a duplicate of another process's file

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

       #include <sys/syscall.h>      /* Definition of SYS_* constants */
       #include <unistd.h>

       int syscall(SYS_pidfd_getfd, int pidfd, int targetfd,
                   unsigned int flags);

       Note: glibc provides no wrapper for pidfd_getfd(), necessitating
       the use of syscall(2).

DESCRIPTION         top

       The pidfd_getfd() system call allocates a new file descriptor in
       the calling process.  This new file descriptor is a duplicate of
       an existing file descriptor, targetfd, in the process referred to
       by the PID file descriptor pidfd.

       The duplicate file descriptor refers to the same open file
       description (see open(2)) as the original file descriptor in the
       process referred to by pidfd.  The two file descriptors thus
       share file status flags and file offset.  Furthermore, operations
       on the underlying file object (for example, assigning an address
       to a socket object using bind(2)) can equally be performed via
       the duplicate file descriptor.

       The close-on-exec flag (FD_CLOEXEC; see fcntl(2)) is set on the
       file descriptor returned by pidfd_getfd().

       The flags argument is reserved for future use.  Currently, it
       must be specified as 0.

       Permission to duplicate another process's file descriptor is
       governed by a ptrace access mode PTRACE_MODE_ATTACH_REALCREDS
       check (see ptrace(2)).

RETURN VALUE         top

       On success, pidfd_getfd() returns a file descriptor (a
       nonnegative integer).  On error, -1 is returned and errno is set
       to indicate the error.

ERRORS         top

       EBADF  pidfd is not a valid PID file descriptor.

       EBADF  targetfd is not an open file descriptor in the process
              referred to by pidfd.

       EINVAL flags is not 0.

       EMFILE The per-process limit on the number of open file
              descriptors has been reached (see the description of
              RLIMIT_NOFILE in getrlimit(2)).

       ENFILE The system-wide limit on the total number of open files
              has been reached.

       EPERM  The calling process did not have
              PTRACE_MODE_ATTACH_REALCREDS permissions (see ptrace(2))
              over the process referred to by pidfd.

       ESRCH  The process referred to by pidfd does not exist (i.e., it
              has terminated and been waited on).

STANDARDS         top


HISTORY         top

       Linux 5.6.

NOTES         top

       For a description of PID file descriptors, see pidfd_open(2).

       The effect of pidfd_getfd() is similar to the use of SCM_RIGHTS
       messages described in unix(7), but differs in the following

       •  In order to pass a file descriptor using an SCM_RIGHTS
          message, the two processes must first establish a UNIX domain
          socket connection.

       •  The use of SCM_RIGHTS requires cooperation on the part of the
          process whose file descriptor is being copied.  By contrast,
          no such cooperation is necessary when using pidfd_getfd().

       •  The ability to use pidfd_getfd() is restricted by a
          PTRACE_MODE_ATTACH_REALCREDS ptrace  access  mode check.

SEE ALSO         top

       clone3(2), dup(2), kcmp(2), pidfd_open(2)

Linux man-pages (unreleased)     (date)                   pidfd_getfd(2)

Pages that refer to this page: dup(2)pidfd_open(2)seccomp_unotify(2)syscalls(2)