Signal number to name?

Question

How can I quickly get signal name from its number? There is strsignal(), but I just want the name, e.g. SIGUSR1

In other words, if we have macros like

Answer 1

My strsignal(3) man page says you can get the names directly from the sys_signame array. Here's a simple example program I wrote to test it:

#include <signal.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>

void upcase(char *s)
{
    while (*s)
    {
        *s = toupper(*s);
        s++;        
    }
}

int main(void)
{    
    for (int sig = 1; sig < NSIG; sig++)
    {
        char *str = strdup(sys_signame[sig]);
        if (!str)
            return -1;

        upcase(str);
        printf("%2d -> SIG%s\n", sig, str);

        free(str);
    }

    return 0;
}

I think this program produces the output you're looking for:

$ ./example 
 1 -> SIGHUP
 2 -> SIGINT
 3 -> SIGQUIT
 4 -> SIGILL
 5 -> SIGTRAP
 6 -> SIGABRT
 7 -> SIGEMT
 8 -> SIGFPE
 9 -> SIGKILL
10 -> SIGBUS
11 -> SIGSEGV
12 -> SIGSYS
13 -> SIGPIPE
14 -> SIGALRM
15 -> SIGTERM
16 -> SIGURG
17 -> SIGSTOP
18 -> SIGTSTP
19 -> SIGCONT
20 -> SIGCHLD
21 -> SIGTTIN
22 -> SIGTTOU
23 -> SIGIO
24 -> SIGXCPU
25 -> SIGXFSZ
26 -> SIGVTALRM
27 -> SIGPROF
28 -> SIGWINCH
29 -> SIGINFO
30 -> SIGUSR1
31 -> SIGUSR2

Answer 2

May be, you can declare a global array, like this

char *signame[]={"INVALID", "SIGHUP", "SIGINT", "SIGQUIT", "SIGILL", "SIGTRAP", "SIGABRT", "SIGBUS", "SIGFPE", "SIGKILL", "SIGUSR1", "SIGSEGV", "SIGUSR2", "SIGPIPE", "SIGALRM", "SIGTERM", "SIGSTKFLT", "SIGCHLD", "SIGCONT", "SIGSTOP", "SIGTSTP", "SIGTTIN", "SIGTTOU", "SIGURG", "SIGXCPU", "SIGXFSZ", "SIGVTALRM", "SIGPROF", "SIGWINCH", "SIGPOLL", "SIGPWR", "SIGSYS", NULL};

and can use it to print signal name in signal handler, like

void sig_handler(int signum){
     printf("Received signal : %s\n", signame[signum]);
}

Answer 3

Tested below code on Ubuntu 16.04 and MIPS and it works fine.

#include <signal.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>

extern const char * const sys_siglist[];

void upcase(char *s)
{
    while (*s)
    {
        *s = toupper(*s);
        s++;
    }
}

int main(void)
{
    int sig;
    /*
       NSIG returns number of signals available in a system
       and it may vary according to platforms;Found on Ubuntu-16.04 it return 65
       where as in MIPS it is 31; Found in both the platforms it leads to core dump
       after signal 31 so limiting scanning of signal till 31 instead of using NSIG
    */
    for (sig = 1; sig < 32; sig++)
    {
        char *str = strdup(sys_siglist[sig]);
        if (!str)
            return -1;

        upcase(str);
        printf("%2d -> SIG%s\n", sig, str);

        free(str);
    }

    return 0;
}

The output of the above code on Ubuntu-16.04 (Intel x86_64 GNU/Linux):

 1 -> SIGHANGUP
 2 -> SIGINTERRUPT
 3 -> SIGQUIT
 4 -> SIGILLEGAL INSTRUCTION
 5 -> SIGTRACE/BREAKPOINT TRAP
 6 -> SIGABORTED
 7 -> SIGBUS ERROR
 8 -> SIGFLOATING POINT EXCEPTION
 9 -> SIGKILLED
10 -> SIGUSER DEFINED SIGNAL 1
11 -> SIGSEGMENTATION FAULT
12 -> SIGUSER DEFINED SIGNAL 2
13 -> SIGBROKEN PIPE
14 -> SIGALARM CLOCK
15 -> SIGTERMINATED
16 -> SIGSTACK FAULT
17 -> SIGCHILD EXITED
18 -> SIGCONTINUED
19 -> SIGSTOPPED (SIGNAL)
20 -> SIGSTOPPED
21 -> SIGSTOPPED (TTY INPUT)
22 -> SIGSTOPPED (TTY OUTPUT)
23 -> SIGURGENT I/O CONDITION
24 -> SIGCPU TIME LIMIT EXCEEDED
25 -> SIGFILE SIZE LIMIT EXCEEDED
26 -> SIGVIRTUAL TIMER EXPIRED
27 -> SIGPROFILING TIMER EXPIRED
28 -> SIGWINDOW CHANGED
29 -> SIGI/O POSSIBLE
30 -> SIGPOWER FAILURE
31 -> SIGBAD SYSTEM CALL

The output of the above code on busybox (MIPS, Cavium):

 1 -> SIGHANGUP
 2 -> SIGINTERRUPT
 3 -> SIGQUIT
 4 -> SIGILLEGAL INSTRUCTION
 5 -> SIGTRACE/BREAKPOINT TRAP
 6 -> SIGABORTED
 7 -> SIGEMT TRAP
 8 -> SIGFLOATING POINT EXCEPTION
 9 -> SIGKILLED
10 -> SIGBUS ERROR
11 -> SIGSEGMENTATION FAULT
12 -> SIGBAD SYSTEM CALL
13 -> SIGBROKEN PIPE
14 -> SIGALARM CLOCK
15 -> SIGTERMINATED
16 -> SIGUSER DEFINED SIGNAL 1
17 -> SIGUSER DEFINED SIGNAL 2
18 -> SIGCHILD EXITED
19 -> SIGPOWER FAILURE
20 -> SIGWINDOW CHANGED
21 -> SIGURGENT I/O CONDITION
22 -> SIGI/O POSSIBLE
23 -> SIGSTOPPED (SIGNAL)
24 -> SIGSTOPPED
25 -> SIGCONTINUED
26 -> SIGSTOPPED (TTY INPUT)
27 -> SIGSTOPPED (TTY OUTPUT)
28 -> SIGVIRTUAL TIMER EXPIRED
29 -> SIGPROFILING TIMER EXPIRED
30 -> SIGCPU TIME LIMIT EXCEEDED
31 -> SIGFILE SIZE LIMIT EXCEEDED