常用：
kill -1
SIGHUP - hangup or exit a foreground running process from a terminal
kill -1 向进程发送SIGHUP signal，对于不同类型的进程可能产生不一样的效果。如果pid对象为daemon，则kill -1 为重新加载配置；如果pid对象为一般进程则为杀掉进程。
kill -1 用来实现reload似乎是约定俗成的。
具体原因参考：https://segmentfault.com/q/1010000002537875，http://lilydjwg.vim-cn.com/articles/linux-c/ch33.html
一般的守护进程都会在收到这个信号时重新加载配置。这是一个习惯，因为 SIGHUP 本来的意义对守信进程没有意义（SIGHUP 是当控制终端失去连接时触发的信号，而守护进程没有控制终端，所以根本用不上）。
kill -9
kill -9 向进程发送SIGKILL信号，表示进程被终止，进程会立即退出。所以kill -9表示强制杀死该进程，这个信号不能被进程捕获也不能被忽略。通常杀进程，让进程退出采用kill -15，急性子的人会直接使用kill -9（斩立决）
kill -15
kill -15 向进程发送SIGTERM信号 ，表示请进程退出关闭，一般进程收到后会自行停止运行并退出。
kill -l 参考：
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
man kill参考：
# man kill
KILL(1) User Commands KILL(1)
NAME
kill - terminate a process
SYNOPSIS
kill [-s signal|-p] [-q sigval] [-a] [--] pid...
kill -l [signal]
DESCRIPTION
The command kill sends the specified signal to the specified process or process group. If no signal is specified, the TERM signal is sent. The TERM signal will kill
processes which do not catch this signal. For other processes, it may be necessary to use the KILL (9) signal, since this signal cannot be caught.
Most modern shells have a builtin kill function, with a usage rather similar to that of the command described here. The '-a' and '-p' options, and the possibility to
specify processes by command name are a local extension.
If sig is 0, then no signal is sent, but error checking is still performed.
OPTIONS
pid... Specify the list of processes that kill should signal. Each pid can be one of five things:
n where n is larger than 0. The process with pid n will be signaled.
0 All processes in the current process group are signaled.
-1 All processes with pid larger than 1 will be signaled.
-n where n is larger than 1. All processes in process group n are signaled. When an argument of the form '-n' is given, and it is meant to denote a
process group, either the signal must be specified first, or the argument must be preceded by a '--' option, otherwise it will be taken as the signal to
send.
commandname
All processes invoked using that name will be signaled.
-s, --signal signal
Specify the signal to send. The signal may be given as a signal name or number.
-l, --list [signal]
Print a list of signal names, or convert signal given as argument to a name. The signals are found in /usr/include/linux/signal.h
-L, --table
Similar to -l, but will print signal names and their corresponding numbers.
-a, --all
Do not restrict the commandname-to-pid conversion to processes with the same uid as the present process.
-p, --pid
Specify that kill should only print the process id (pid) of the named processes, and not send any signals.
-q, --queue sigval
Use sigqueue(2) rather than kill(2) and the sigval argument is used to specify an integer to be sent with the signal. If the receiving process has installed a
handler for this signal using the SA_SIGINFO flag to sigaction(2), then it can obtain this data via the si_value field of the siginfo_t structure.
NOTES
It is not possible to send a signal to explicitly selected thread in a multithreaded process by kill(2) syscall. If kill(2) is used to send a signal to a thread
group, then kernel selects arbitrary member of the thread group that has not blocked the signal. For more details see clone(2) CLONE_THREAD description.
The command kill(1) as well as syscall kill(2) accepts TID (thread ID, see gettid(2)) as argument. In this case the kill behavior is not changed and the signal is
also delivered to the thread group rather than to the specified thread.
SEE ALSO
bash(1), tcsh(1), kill(2), sigvec(2), signal(7)
AUTHOR
Taken from BSD 4.4. The ability to translate process names to process ids was added by Salvatore Valente ⟨svalente@mit.edu⟩.
AVAILABILITY
The kill command is part of the util-linux package and is available from Linux Kernel Archive ⟨ftp://ftp.kernel.org/pub/linux/utils/util-linux/⟩.
util-linux March 2013 KILL(1)