366 lines
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366 lines
8.2 KiB
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML><HEAD><TITLE>Man page of PIDFD_SEND_SIGNAL</TITLE>
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</HEAD><BODY>
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<H1>PIDFD_SEND_SIGNAL</H1>
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Section: Linux Programmer's Manual (2)<BR>Updated: 2019-09-19<BR><A HREF="#index">Index</A>
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<A HREF="/cgi-bin/man/man2html">Return to Main Contents</A><HR>
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<A NAME="lbAB"> </A>
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<H2>NAME</H2>
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pidfd_send_signal - send a signal to a process specified by a file descriptor
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<A NAME="lbAC"> </A>
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<H2>SYNOPSIS</H2>
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<PRE>
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<B>#include <<A HREF="file:///usr/include/signal.h">signal.h</A>></B>
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<B>int pidfd_send_signal(int </B><I>pidfd</I><B>, int </B><I>sig</I><B>, siginfo_t *</B><I>info</I><B>,</B>
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<B> unsigned int </B><I>flags</I><B>);</B>
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</PRE>
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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The
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<B>pidfd_send_signal</B>()
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system call sends the signal
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<I>sig</I>
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to the target process referred to by
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<I>pidfd</I>,
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a PID file descriptor that refers to a process.
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<P>
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If the
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<I>info</I>
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argument points to a
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<I>siginfo_t</I>
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buffer, that buffer should be populated as described in
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<B><A HREF="/cgi-bin/man/man2html?2+rt_sigqueueinfo">rt_sigqueueinfo</A></B>(2).
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<P>
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If the
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<I>info</I>
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argument is a NULL pointer,
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this is equivalent to specifying a pointer to a
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<I>siginfo_t</I>
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buffer whose fields match the values that are
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implicitly supplied when a signal is sent using
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<B><A HREF="/cgi-bin/man/man2html?2+kill">kill</A></B>(2):
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<P>
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<DL COMPACT>
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<DT id="1">*<DD>
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<I>si_signo</I>
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is set to the signal number;
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<DT id="2">*<DD>
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<I>si_errno</I>
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is set to 0;
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<DT id="3">*<DD>
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<I>si_code</I>
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is set to
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<B>SI_USER;</B>
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<DT id="4">*<DD>
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<I>si_pid</I>
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is set to the caller's PID; and
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<DT id="5">*<DD>
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<I>si_uid</I>
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is set to the caller's real user ID.
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</DL>
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<P>
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The calling process must either be in the same PID namespace as the
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process referred to by
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<I>pidfd</I>,
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or be in an ancestor of that namespace.
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<P>
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The
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<I>flags</I>
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argument is reserved for future use;
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currently, this argument must be specified as 0.
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<A NAME="lbAE"> </A>
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<H2>RETURN VALUE</H2>
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On success,
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<B>pidfd_send_signal</B>()
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returns 0.
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On error, -1 is returned and
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<I>errno</I>
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is set to indicate the cause of the error.
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<A NAME="lbAF"> </A>
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<H2>ERRORS</H2>
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<DL COMPACT>
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<DT id="6"><B>EBADF</B>
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<DD>
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<I>pidfd</I>
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is not a valid PID file descriptor.
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<DT id="7"><B>EINVAL</B>
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<DD>
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<I>sig</I>
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is not a valid signal.
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<DT id="8"><B>EINVAL</B>
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<DD>
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The calling process is not in a PID namespace from which it can
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send a signal to the target process.
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<DT id="9"><B>EINVAL</B>
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<DD>
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<I>flags</I>
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is not 0.
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<DT id="10"><B>EPERM</B>
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<DD>
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The calling process does not have permission to send the signal
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to the target process.
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<DT id="11"><B>EPERM</B>
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<DD>
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<I>pidfd</I>
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doesn't refer to the calling process, and
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<I>info.si_code</I>
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is invalid (see
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<B><A HREF="/cgi-bin/man/man2html?2+rt_sigqueueinfo">rt_sigqueueinfo</A></B>(2)).
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<DT id="12"><B>ESRCH</B>
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<DD>
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The target process does not exist
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(i.e., it has terminated and been waited on).
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</DL>
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<A NAME="lbAG"> </A>
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<H2>VERSIONS</H2>
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<B>pidfd_send_signal</B>()
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first appeared in Linux 5.1.
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<A NAME="lbAH"> </A>
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<H2>CONFORMING TO</H2>
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<B>pidfd_send_signal</B>()
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is Linux specific.
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<A NAME="lbAI"> </A>
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<H2>NOTES</H2>
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Currently, there is no glibc wrapper for this system call; call it using
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<B><A HREF="/cgi-bin/man/man2html?2+syscall">syscall</A></B>(2).
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<A NAME="lbAJ"> </A>
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<H3>PID file descriptors</H3>
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The
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<I>pidfd</I>
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argument is a PID file descriptor,
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a file descriptor that refers to process.
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Such a file descriptor can be obtained in any of the following ways:
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<DL COMPACT>
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<DT id="13">*<DD>
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by opening a
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<I>/proc/[pid]</I>
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directory;
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<DT id="14">*<DD>
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using
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<B><A HREF="/cgi-bin/man/man2html?2+pidfd_open">pidfd_open</A></B>(2);
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or
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<DT id="15">*<DD>
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via the PID file descriptor that is returned by a call to
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<B><A HREF="/cgi-bin/man/man2html?2+clone">clone</A></B>(2)
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or
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<B><A HREF="/cgi-bin/man/man2html?2+clone3">clone3</A></B>(2)
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that specifies the
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<B>CLONE_PIDFD</B>
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flag.
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</DL>
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<P>
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The
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<B>pidfd_send_signal</B>()
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system call allows the avoidance of race conditions that occur
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when using traditional interfaces (such as
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<B><A HREF="/cgi-bin/man/man2html?2+kill">kill</A></B>(2))
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to signal a process.
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The problem is that the traditional interfaces specify the target process
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via a process ID (PID),
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with the result that the sender may accidentally send a signal to
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the wrong process if the originally intended target process
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has terminated and its PID has been recycled for another process.
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By contrast,
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a PID file descriptor is a stable reference to a specific process;
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if that process terminates,
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<B>pidfd_send_signal</B>()
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fails with the error
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<B>ESRCH</B>.
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<A NAME="lbAK"> </A>
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<H2>EXAMPLE</H2>
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<PRE>
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#define _GNU_SOURCE
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#include <<A HREF="file:///usr/include/limits.h">limits.h</A>>
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#include <<A HREF="file:///usr/include/signal.h">signal.h</A>>
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#include <<A HREF="file:///usr/include/fcntl.h">fcntl.h</A>>
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#include <<A HREF="file:///usr/include/stdio.h">stdio.h</A>>
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#include <<A HREF="file:///usr/include/string.h">string.h</A>>
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#include <<A HREF="file:///usr/include/stdlib.h">stdlib.h</A>>
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#include <<A HREF="file:///usr/include/unistd.h">unistd.h</A>>
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#include <<A HREF="file:///usr/include/sys/syscall.h">sys/syscall.h</A>>
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#ifndef __NR_pidfd_send_signal
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#define __NR_pidfd_send_signal 424
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#endif
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static int
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pidfd_send_signal(int pidfd, int sig, siginfo_t *info,
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unsigned int flags)
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{
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return syscall(__NR_pidfd_send_signal, pidfd, sig, info, flags);
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}
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int
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main(int argc, char *argv[])
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{
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siginfo_t info;
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char path[PATH_MAX];
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int pidfd, sig;
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if (argc != 3) {
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fprintf(stderr, "Usage: %s <pid> <signal>\n", argv[0]);
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exit(EXIT_FAILURE);
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}
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sig = atoi(argv[2]);
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/* Obtain a PID file descriptor by opening the /proc/PID directory
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of the target process */
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snprintf(path, sizeof(path), "/proc/%s", argv[1]);
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pidfd = open(path, O_RDONLY);
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if (pidfd == -1) {
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perror("open");
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exit(EXIT_FAILURE);
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}
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/* Populate a 'siginfo_t' structure for use with
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pidfd_send_signal() */
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memset(&info, 0, sizeof(info));
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info.si_code = SI_QUEUE;
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info.si_signo = sig;
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info.si_errno = 0;
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info.si_uid = getuid();
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info.si_pid = getpid();
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info.si_value.sival_int = 1234;
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/* Send the signal */
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if (pidfd_send_signal(pidfd, sig, &info, 0) == -1) {
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perror("pidfd_send_signal");
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exit(EXIT_FAILURE);
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}
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exit(EXIT_SUCCESS);
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}
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</PRE>
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<A NAME="lbAL"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?2+clone">clone</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+kill">kill</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+pidfd_open">pidfd_open</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+rt_sigqueueinfo">rt_sigqueueinfo</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+sigaction">sigaction</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?7+pid_namespaces">pid_namespaces</A></B>(7),
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<B><A HREF="/cgi-bin/man/man2html?7+signal">signal</A></B>(7)
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<A NAME="lbAM"> </A>
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<H2>COLOPHON</H2>
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This page is part of release 5.05 of the Linux
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<I>man-pages</I>
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project.
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A description of the project,
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information about reporting bugs,
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and the latest version of this page,
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can be found at
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<A HREF="https://www.kernel.org/doc/man-pages/.">https://www.kernel.org/doc/man-pages/.</A>
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<P>
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<HR>
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<A NAME="index"> </A><H2>Index</H2>
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<DL>
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<DT id="16"><A HREF="#lbAB">NAME</A><DD>
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<DT id="17"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="18"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="19"><A HREF="#lbAE">RETURN VALUE</A><DD>
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<DT id="20"><A HREF="#lbAF">ERRORS</A><DD>
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<DT id="21"><A HREF="#lbAG">VERSIONS</A><DD>
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<DT id="22"><A HREF="#lbAH">CONFORMING TO</A><DD>
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<DT id="23"><A HREF="#lbAI">NOTES</A><DD>
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<DL>
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<DT id="24"><A HREF="#lbAJ">PID file descriptors</A><DD>
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</DL>
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<DT id="25"><A HREF="#lbAK">EXAMPLE</A><DD>
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<DT id="26"><A HREF="#lbAL">SEE ALSO</A><DD>
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<DT id="27"><A HREF="#lbAM">COLOPHON</A><DD>
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</DL>
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<HR>
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This document was created by
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<A HREF="/cgi-bin/man/man2html">man2html</A>,
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using the manual pages.<BR>
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Time: 00:05:33 GMT, March 31, 2021
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</BODY>
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</HTML>
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