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I know what kill -9 means, but anyone can explain what does kill -3 mean? Is there any special signal it sends out?

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  • 7
    Have you tried man kill?
    – Tamara Wijsman
    Oct 31, 2011 at 13:24
  • 7
    @TomWijsman, man kill doesn't list the signals and man signals doesn't show anything at all. This is actually the first useful thin that comes up with you search google for "kill -3". :) It is really easy to over look the 'kill -l' option, especially if you didn't know much about signals ahead of time.
    – Ape-inago
    Jul 26, 2013 at 14:34
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    @Ape-inago: It is short enough to not skip over an option, but granted clarifying what to look for helps, thanks; kill -l indeed lists a summary, if you were wondering man 7 signal does list them in detail. It is where the table in the currently accepted answer likely comes from.
    – Tamara Wijsman
    Aug 6, 2013 at 21:40

3 Answers 3

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The signals described in the original POSIX.1-1990 standard:

   Signal     Value     Action   Comment
   -------------------------------------------------------------------------
   SIGHUP        1       Term    Hangup detected on controlling terminal
                                 or death of controlling process
   SIGINT        2       Term    Interrupt from keyboard
   SIGQUIT       3       Core    Quit from keyboard
   SIGILL        4       Core    Illegal Instruction
   SIGABRT       6       Core    Abort signal from abort(3)
   SIGFPE        8       Core    Floating point exception
   SIGKILL       9       Term    Kill signal
   SIGSEGV      11       Core    Invalid memory reference
   SIGPIPE      13       Term    Broken pipe: write to pipe with no readers
   SIGALRM      14       Term    Timer signal from alarm(2)
   SIGTERM      15       Term    Termination signal
   SIGUSR1   30,10,16    Term    User-defined signal 1
   SIGUSR2   31,12,17    Term    User-defined signal 2
   SIGCHLD   20,17,18    Ign     Child stopped or terminated
   SIGCONT   19,18,25    Cont    Continue if stopped
   SIGSTOP   17,19,23    Stop    Stop process
   SIGTSTP   18,20,24    Stop    Stop typed at tty
   SIGTTIN   21,21,26    Stop    tty input for background process
   SIGTTOU   22,22,27    Stop    tty output for background process
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  • 6
    Unfortunately, the numeric values of these signals vary between operating systems and even between architectures.
    – u1686_grawity
    Oct 30, 2011 at 18:06
25

kill -3 is a thread dump that will list all the Java threads that are currently active in Java Virtual Machine (JVM).

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20

kill -l shows us all signals. Following this hint 3 means SIGQUIT

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