Linux信号(一)：信号类型
首先我们用 kill -l 命令来看看，linux系统有哪些信号：
root@1204nStrive:~# kill -l
1) SIGHUP 2) SIGINT 3) SIGQUIT 4) SIGILL 5) SIGTRAP
6) SIGABRT 7) SIGBUS 8) SIGFPE 9) SIGKILL 10) SIGUSR1
11) SIGSEGV 12) SIGUSR2 13) SIGPIPE 14) SIGALRM 15) SIGTERM
16) SIGSTKFLT 17) SIGCHLD 18) SIGCONT 19) SIGSTOP 20) SIGTSTP
21) SIGTTIN 22) SIGTTOU 23) SIGURG 24) SIGXCPU 25) SIGXFSZ
26) SIGVTALRM 27) SIGPROF 28) SIGWINCH 29) SIGIO 30) SIGPWR
31) SIGSYS 34) SIGRTMIN 35) SIGRTMIN+1 36) SIGRTMIN+2 37) SIGRTMIN+3
38) SIGRTMIN+4 39) SIGRTMIN+5 40) SIGRTMIN+6 41) SIGRTMIN+7 42) SIGRTMIN+8
43) SIGRTMIN+9 44) SIGRTMIN+10 45) SIGRTMIN+11 46) SIGRTMIN+12 47) SIGRTMIN+13
48) SIGRTMIN+14 49) SIGRTMIN+15 50) SIGRTMAX-14 51) SIGRTMAX-13 52) SIGRTMAX-12
53) SIGRTMAX-11 54) SIGRTMAX-10 55) SIGRTMAX-9 56) SIGRTMAX-8 57) SIGRTMAX-7
58) SIGRTMAX-6 59) SIGRTMAX-5 60) SIGRTMAX-4 61) SIGRTMAX-3 62) SIGRTMAX-2
63) SIGRTMAX-1 64) SIGRTMAX
各信号值实际定义及含义在signum.h头文件中：
root@1204nStrive:~# more /usr/include/x86_64-linux-gnu/bits/signum.h
/* Signal number definitions. Linux version.
Copyright (C) 1995,1996,1997,1998,1999,2003 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, write to the Free
Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA. */
#ifdef _SIGNAL_H
/* 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_UNIX98
# define SIG_HOLD ((__sighandler_t) 2) /* Add signal to hold mask. */
#endif
/* Signals. */
#define SIGHUP 1 /* Hangup (POSIX). */
#define SIGINT 2 /* Interrupt (ANSI). */
#define SIGQUIT 3 /* Quit (POSIX). */
#define SIGILL 4 /* Illegal instruction (ANSI). */
#define SIGTRAP 5 /* Trace trap (POSIX). */
#define SIGABRT 6 /* Abort (ANSI). */
#define SIGIOT 6 /* IOT trap (4.2 BSD). */
#define SIGBUS 7 /* BUS error (4.2 BSD). */
#define SIGFPE 8 /* Floating-point exception (ANSI). */
#define SIGKILL 9 /* Kill, unblockable (POSIX). */
#define SIGUSR1 10 /* User-defined signal 1 (POSIX). */
#define SIGSEGV 11 /* Segmentation violation (ANSI). */
#define SIGUSR2 12 /* User-defined signal 2 (POSIX). */
#define SIGPIPE 13 /* Broken pipe (POSIX). */
#define SIGALRM 14 /* Alarm clock (POSIX). */
#define SIGTERM 15 /* Termination (ANSI). */
#define SIGSTKFLT 16 /* Stack fault. */
#define SIGCLD SIGCHLD /* Same as SIGCHLD (System V). */
#define SIGCHLD 17 /* Child status has changed (POSIX). */
#define SIGCONT 18 /* Continue (POSIX). */
#define SIGSTOP 19 /* Stop, unblockable (POSIX). */
#define SIGTSTP 20 /* Keyboard stop (POSIX). */
#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). */
#define SIGXFSZ 25 /* File size limit exceeded (4.2 BSD). */
#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 ())
/* These are the hard limits of the kernel. These values should not be
used directly at user level. */
#define __SIGRTMIN 32
#define __SIGRTMAX (_NSIG - 1)
#endif /* included. */
现在来学习一下这个头文件，首先是伪信号函数：
#define SIG_ERR ((__sighandler_t) -1) /* Error return. */
#define SIG_DFL ((__sighandler_t) 0) /* Default action. */
#define SIG_IGN ((__sighandler_t) 1) /* Ignore signal. */
当信号发生时，我们可以用信号处理函数捕捉该信号，当信号处理函数
= SIG_IGN，表示我们忽略该信号，系统中大多数信号都是使用该处理方式进行处理的，但是，SIGKILL，SIGSTOP信号不能被忽略。
= SIG_DFL，表示执行系统默认动作。
定义我们自己的信号处理函数，捕捉信号。
下图给出这些当系统产生信号时，系统的默认动作：
接下来是信号的详细说明
/* 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 ())
注意最后两行，分别代表实时信号的最小值和实时信号的最大值，从kill -l 命令中可以看出，在我们linux系统中，SIGRTMIN值为34，SIGRTMAX 值为65：
#define SIGRTMIN (__libc_current_sigrtmin ())
#define SIGRTMAX (__libc_current_sigrtmax ())