linux command of the difference between kill and kill -9
Reprinted from https://www.cnblogs.com/liuhouhou/p/5400540.html
I am sure you are very familiar with the kill -9, they are often used at work. Especially when you go to restart tomcat. But mostly it seems, our understanding of -9 only the surface of it.
Few people (including me) to look seriously kill -n n in the end this is what stuff. Self-criticism about.
Ok. Let's good to know about this familiar stranger.
1）kill
From the help you can clearly see the -n refers to the signal number, then the question is, "No signal" Who is the god? ? ?
2) kill -l (see Linux / Unix signal variable)
So much ah! ! Today alone talk about SIGTERM and SIGKILL
3）（kill pid） 、（ kill -15 pid）
The system program will send a signal to the corresponding SIGTERM. When the program receives this signal, the following things will happen
- Program immediately stop
- When the program stops and then release the appropriate resources
- The program may continue to run
Most of the program after receiving the SIGTERM signal, will first release their own resources, and then stop. But there are also programs may, after receiving the semaphore and do some other things, and these things can be
Configuration. If the program is waiting for IO, you may not immediately make the appropriate.
That is to say, SIGTERM mostly be blocked, ignored.
4）kill -9 pid
You can not not respond to SIGTERM it? ? Well, I will give you a kill order, I see you do not obediently. Most admin can use this command
However, not all programs will obediently toe the line, there is always a program in those states not appropriate immediately.
appendix:
linux signals
| Signal Name | Number | Description |
| Sigःuf | 1 | Hangup (POSIX) |
| SIGINT | 2 | Terminal interrupt (ANSI) |
| SIGQUIT | 3 | Terminal quit (POSIX) |
| SEAL | 4 | Illegal instruction (ANSI) |
| SIGTRAP | 5 | Trace trap (POSIX) |
| SIGIOT | 6 | IOT Trap (4.2 BSD) |
| SIGBUS | 7 | BUS error (4.2 BSD) |
| SIGFPE | 8 | Floating point exception (ANSI) |
| SIGKILL | 9 | Kill(can't be caught or ignored) (POSIX) |
| SIGUSR1 | 10 | User defined signal 1 (POSIX) |
| SIGSEGV | 11 | Invalid memory segment access (ANSI) |
| SIGUSR2 | 12 | User defined signal 2 (POSIX) |
| SIGPIPE | 13 | Write on a pipe with no reader, Broken pipe (POSIX) |
| SIGALRM | 14 | Alarm clock (POSIX) |
| SIGTERM | 15 | Termination (ANSI) |
| SIGSTKFLT | 16 | Stack fault |
| SIGCHLD | 17 | Child process has stopped or exited, changed (POSIX) |
| SIGCONT | 18 | Continue executing, if stopped (POSIX) |
| SIGSTOP | 19 | Stop executing(can't be caught or ignored) (POSIX) |
| SIGTSTP | 20 | Terminal stop signal (POSIX) |
| SIGTTIN | 21 | Background process trying to read, from TTY (POSIX) |
| SIGTTOU | 22 | Background process trying to write, to TTY (POSIX) |
| Sigurd | 23 | Urgent condition on socket (4.2 BSD) |
| SIGXCPU | 24 | CPU limit exceeded (4.2 BSD) |
| SIGXFSZ | 25 | File size limit exceeded (4.2 BSD) |
| SIGVTALRM | 26 | Virtual alarm clock (4.2 BSD) |
| SIGPROF | 27 | Profiling alarm clock (4.2 BSD) |
| SIGWINCH | 28 | Window size change (4.3 BSD, Sun) |
| SIGIO | 29 | I/O now possible (4.2 BSD) |
| SIGPWR | 30 | Power failure restart (System V) |