一.信号的基本概念

信号是系统响应某个条件而产生的事件，进程接收到信号会执行相应的操作。

与信号调用有关的系统调用在“ signal.h”头文件中有声明。

二.信号的引发

键盘事件 ctrl +c ctrl +\
非法内存如果内存管理出错，系统就会发送一个信号进行处理
硬件故障同样的，硬件出现故障系统也会产生一个信号
环境切换比如说从用户态切换到其他态，状态的改变也会发送一个信号，这个信号会告知给系统。

三.常见信号主要功能与对应的值

在这里插入图片描述

#define SIGHUP 1
#define SIGINT 2 //键盘按下 Ctrl+c 时，会产生该信号
#define SIGQUIT 3
#define SIGILL 4
#define SIGTRAP 5
#define SIGABRT 6
#define SIGIOT 6
#define SIGBUS 7
#define SIGFPE 8
#define SIGKILL 9 //该信号的响应方式不允许改变
#define SIGUSR1 10
#define SIGSEGV 11
#define SIGUSR2 12
#define SIGPIPE 13 //读端关闭的描述符，写端写入时产生，该信号会终止程序
#define SIGALRM 14
#define SIGTERM 15 //系统 kill 命令默认发送的信号
#define SIGSTKFLT 16
#define SIGCHLD 17 //子进程结束后，会默认给父进程发送该信号
#define SIGCONT 18
#define SIGSTOP 19
#define SIGTSTP 20
#define SIGTTIN 21
#define SIGTTOU 22
#define SIGURG 23

四.修改信号的相应方式——signal()

利用signal()可以将指定的信号进行修改

忽略信号：SIG_IGN

默认处理：SIG_DFL

自定义的：自己写的信号处理函数

在键盘上按下 Ctrl+c 时，会给当前终端前台执行的进程发送 SIGINT 信号，用 signal 修改 SIGINT 信号的响应方式示例代码如下：

#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<assert.h>
void fun(int sign)
{
    
    
    printf("fun was called, sign = %d\n", sign);
}
int main()
{
    
    
    signal(SIGINT, fun);
    while(1)
    {
    
    
    sleep(1);
    printf("main running\n");
    }
    exit(0);
}

运行结果：
在这里插入图片描述

五.发送信号 – kill()

kill() 可以向指定的进程发送指定的信号‘
int kill(pid_t pid,int sig);

pid > 0 指定将信号发送个那个进程

pid == 0 信号被发送到和当前进程在同一个进程组的进程

pid == -1 将信号发送给系统上有权限发送的所有的进程

pid < -1 将信号发送给进程组 id 等于 pid 绝对值，并且有权限发送的所有的进程。

sig 指定发送信号的类型。

附64个信号类型及作用详细说明


> root@myj:/usr/include/x86_64-linux-gnu/bits# cat signum-generic.h  /*
> Signal number constants.  Generic template.    Copyright (C) 1991-2018
> Free Software Foundation, Inc.    This file is part of the GNU C
> Library.
> 
>    The GNU C Library is free software; you can redistribute it and/or 
> modify it under the terms of the GNU Lesser General Public    License
> as published by the Free Software Foundation; either    version 2.1 of
> the License, or (at your option) any later version.
> 
>    The GNU C Library is distributed in the hope that it will be
> useful,    but WITHOUT ANY WARRANTY; without even the implied warranty
> of    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> GNU    Lesser General Public License for more details.
> 
>    You should have received a copy of the GNU Lesser General Public   
> License along with the GNU C Library; if not, see   
> <http://www.gnu.org/licenses/>.  */
> 
> #ifndef _BITS_SIGNUM_GENERIC_H
> #define _BITS_SIGNUM_GENERIC_H 1
> 
> #ifndef _SIGNAL_H
> #error "Never include <bits/signum-generic.h> directly; use <signal.h> instead."
> #endif
> 
> /* Fake signal functions.  */
> 
> #define SIG_ERR  ((__sighandler_t) -1)  /* Error return.  */
> #define SIG_DFL  ((__sighandler_t)  0)  /* Default action.  */
> #define SIG_IGN  ((__sighandler_t)  1)  /* Ignore signal.  */
> 
> #ifdef __USE_XOPEN
> # define SIG_HOLD ((__sighandler_t) 2)  /* Add signal to hold mask.  */
> #endif
> 
> /* We define here all the signal names listed in POSIX (1003.1-2008); 
> as of 1003.1-2013, no additional signals have been added by POSIX.   
> We also define here signal names that historically exist in every   
> real-world POSIX variant (e.g. SIGWINCH).
> 
>    Signals in the 1-15 range are defined with their historical
> numbers.    For other signals, we use the BSD numbers.    There are
> two unallocated signal numbers in the 1-31 range: 7 and 29.    Signal
> number 0 is reserved for use as kill(pid, 0), to test whether    a
> process exists without sending it a signal.  */
> 
> /* ISO C99 signals.  */
> #define SIGINT          2       /* Interactive attention signal.  */
> #define SIGILL          4       /* Illegal instruction.  */
> #define SIGABRT         6       /* Abnormal termination.  */
> #define SIGFPE          8       /* Erroneous arithmetic operation.  */
> #define SIGSEGV         11      /* Invalid access to storage.  */
> #define SIGTERM         15      /* Termination request.  */
> 
> /* Historical signals specified by POSIX. */
> #define SIGHUP          1       /* Hangup.  */
> #define SIGQUIT         3       /* Quit.  */
> #define SIGTRAP         5       /* Trace/breakpoint trap.  */
> #define SIGKILL         9       /* Killed.  */
> #define SIGBUS          10      /* Bus error.  */
> #define SIGSYS          12      /* Bad system call.  */
> #define SIGPIPE         13      /* Broken pipe.  */
> #define SIGALRM         14      /* Alarm clock.  */
> 
> /* New(er) POSIX signals (1003.1-2008, 1003.1-2013).  */
> #define SIGURG          16      /* Urgent data is available at a socket.  */
> #define SIGSTOP         17      /* Stop, unblockable.  */
> #define SIGTSTP         18      /* Keyboard stop.  */
> #define SIGCONT         19      /* Continue.  */
> #define SIGCHLD         20      /* Child terminated or stopped.  */
> #define SIGTTIN         21      /* Background read from control terminal.  */
> #define SIGTTOU         22      /* Background write to control terminal.  */
> #define SIGPOLL         23      /* Pollable event occurred (System V).  */
> #define SIGXCPU         24      /* CPU time limit exceeded.  */
> #define SIGXFSZ         25      /* File size limit exceeded.  */
> #define SIGVTALRM       26      /* Virtual timer expired.  */
> #define SIGPROF         27      /* Profiling timer expired.  */
> #define SIGUSR1         30      /* User-defined signal 1.  */
> #define SIGUSR2         31      /* User-defined signal 2.  */
> 
> /* Nonstandard signals found in all modern POSIX systems    (including
> both BSD and Linux).  */
> #define SIGWINCH        28      /* Window size change (4.3 BSD, Sun).  */
> 
> /* Archaic names for compatibility.  */
> #define SIGIO           SIGPOLL /* I/O now possible (4.2 BSD).  */
> #define SIGIOT          SIGABRT /* IOT instruction, abort() on a PDP-11.  */
> #define SIGCLD          SIGCHLD /* Old System V name */
> 
> /* Not all systems support real-time signals.  bits/signum.h indicates
> that they are supported by overriding __SIGRTMAX to a value greater   
> than __SIGRTMIN.  These constants give the kernel-level hard limits,  
> but some real-time signals may be used internally by glibc.  Do not   
> use these constants in application code; use SIGRTMIN and SIGRTMAX   
> (defined in signal.h) instead.  */
> #define __SIGRTMIN      32
> #define __SIGRTMAX      __SIGRTMIN
> 
> /* Biggest signal number + 1 (including real-time signals).  */
> #define _NSIG           (__SIGRTMAX + 1)
> 
> #endif /* bits/signum-generic.h.  */
> #define SIG_ERR ((__sighandler_t) -1) /* Error return. /
> #define SIG_DFL ((__sighandler_t) 0) / Default action. /
> #define SIG_IGN ((__sighandler_t) 1) / Ignore signal. */

/* Signals.  */
#define SIGHUP          1       /* Hangup (POSIX).  终端连接断开信号*/
#define SIGINT          2       /* Interrupt (ANSI).  中断信号，终端中输入ctrl+c，可中断前台进程*/
#define SIGQUIT         3       /* Quit (POSIX).   退出信号，终端中输入ctrl+\，可退出前台进程，同时产生core文件*/
#define SIGILL          4       /* Illegal instruction (ANSI). 非法指令信号，4.3BSD的abort函数产生该信号 */
#define SIGTRAP         5       /* Trace trap (POSIX).  调试信号，当在程序中设置断点后，该信号使得调试程序获得控制权*/
#define SIGABRT         6       /* Abort (ANSI). 程序异常终止信号，abort函数产生该信号 */
#define SIGIOT          6       /* IOT trap (4.2 BSD).  功能同SIGABRT*/
#define SIGBUS          7       /* BUS error (4.2 BSD).  程序访问不存在的内存区域时，产生该信号*/
#define SIGFPE          8       /* Floating-point exception (ANSI).  算术异常，如除以0*/
#define SIGKILL         9       /* Kill, unblockable (POSIX).  不能被忽略，非阻塞，可杀死任意一个运行中的进程*/
#define SIGUSR1         10      /* User-defined signal 1 (POSIX).  用户自定义1*/
#define SIGSEGV         11      /* Segmentation violation (ANSI). 当程序访问没有访问权限的内存区域，或者访问非可读的内存区域时，产生该信号，如数组越界 */
#define SIGUSR2         12      /* User-defined signal 2 (POSIX). 用户自定义2 */
#define SIGPIPE         13      /* Broken pipe (POSIX). 当管道读端已关闭，继续往管道中写，产生该信号 */
#define SIGALRM         14      /* Alarm clock (POSIX). alarm函数超时时产生该信号，默认动作是程序终止 */
#define SIGTERM         15      /* Termination (ANSI).  终止程序信号，命令kill默认使用该参数*/
#define SIGSTKFLT       16      /* Stack fault.  */
#define SIGCLD          SIGCHLD /* Same as SIGCHLD (System V).  */
#define SIGCHLD         17      /* Child status has changed (POSIX).  子进程终止或停止时，产生该信号，默认被忽略*/
#define SIGCONT         18      /* Continue (POSIX).  */
#define SIGSTOP         19      /* Stop, unblockable (POSIX).  停止一个作业控制进程*/
#define SIGTSTP         20      /* Keyboard stop (POSIX).  ctrl+z产生该信号，改信号使得前台进程挂起*/
#define SIGTTIN         21      /* Background read from tty (POSIX).  */
#define SIGTTOU         22      /* Background write to tty (POSIX).  */
#define SIGURG          23      /* Urgent condition on socket (4.2 BSD).  */
#define SIGXCPU         24      /* CPU limit exceeded (4.2 BSD).  进程超过了CPU软限制产生该信号*/
#define SIGXFSZ         25      /* File size limit exceeded (4.2 BSD).  进程超过了文件大小软限制产生该信号*/
#define SIGVTALRM       26      /* Virtual alarm clock (4.2 BSD).  */
#define SIGPROF         27      /* Profiling alarm clock (4.2 BSD).  */
#define SIGWINCH        28      /* Window size change (4.3 BSD, Sun).  */
#define SIGPOLL         SIGIO   /* Pollable event occurred (System V).  */
#define SIGIO           29      /* I/O now possible (4.2 BSD).  */
#define SIGPWR          30      /* Power failure restart (System V).  */
#define SIGSYS          31      /* Bad system call.  */
#define SIGUNUSED       31

#define _NSIG           65      /* Biggest signal number + 1
                                   (including real-time signals).  */

#define SIGRTMIN        (__libc_current_sigrtmin ())
#define SIGRTMAX        (__libc_current_sigrtmax ())

Linux信号总结及信号的使用

目录