pidfd_getfd(2) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON

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

NAME         top

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

SYNOPSIS         top

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

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 cause of 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).

VERSIONS         top

       pidfd_getfd() first appeared in Linux 5.6.

CONFORMING TO         top

       pidfd_getfd() is Linux specific.

NOTES         top

       Currently, there is no glibc wrapper for this system call; call
       it using syscall(2).

       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.

SEE ALSO         top

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

COLOPHON         top

       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
       https://www.kernel.org/doc/man-pages/.

Linux                          2020-03-31                 PIDFD_GETFD(2)

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