PIDFD_GETFD(2)              Linux Programmer's Manual             PIDFD_GETFD(2)

       pidfd_getfd - obtain a duplicate of another process's file descriptor

       int pidfd_getfd(int pidfd, int targetfd, unsigned int flags);

       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)).

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

       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

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

       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).

       pidfd_getfd() first appeared in Linux 5.6.

       pidfd_getfd() is Linux specific.

       Currently, there is no glibc wrapper for this system call; call it using

       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 respects:

       • 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.

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

       This page is part of release 5.10 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

Linux                              2020-03-31                     PIDFD_GETFD(2)