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 SIGUSR1 -> 12 do we have anything like 12 -> SIGUSR1 ?

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

glib 2.32 (released on 2020-08-05) introduced the function sigabbrev_np(int). Since that version you cannot use sys_siglist[] anymore too.

From man strsignal:

The sigabbrev_np() function returns the abbreviated name of the signal, sig. For example, given the value SIGINT, it returns the string "INT".
[...]
sigdescr_np() and sigdabbrev_np() first appeared in glibc 2.32. Starting with version 2.32, the sys_siglist symbol is no longer exported by glibc.

And from the release notes:

The functions sigabbrev_np and sigdescr_np have been added. The sigabbrev_np returns the abbreviated signal name (e.g. "HUP" for SIGHUP) [...] both functions return NULL for an invalid signal number.

They should be used instead of sys_siglist or sys_sigabbrev and they are both thread and async-signal safe. These functions are GNU extensions.