strsignal / psignal / sigdescr_np / sigabbrev_np (3) - glibc

Split from the chapter glibc: strings, ctype and stdlib arithmetic into the per-function layout; see the method page and the glibc ledger for coverage status.

Declaration and gates

#include <string.h>
char *strsignal(int sig);                /* __USE_XOPEN2K8 in string.h */
const char *sigdescr_np(int sig);        /* __USE_GNU */
const char *sigabbrev_np(int sig);       /* __USE_GNU */

#include <signal.h>
void psignal(int sig, const char *s);    /* _DEFAULT_SOURCE since 2.19 */

Gate history per strsignal(3)/psignal(3) SYNOPSIS: strsignal _POSIX_C_SOURCE >= 200809L (glibc 2.10-2.31), _GNU_SOURCE before; psignal _DEFAULT_SOURCE since glibc 2.19, _BSD_SOURCE || _SVID_SOURCE before.

Semantics

strsignal returns a message describing signal sig, localized via LC_MESSAGES; the string is valid only until the next strsignal call and must not be modified (strsignal(3), manual signal.texi Signal Messages). psignal prints s: <description> to stderr, omitting the prefix when s is NULL or empty (psignal(3)). sigdescr_np returns the untranslated description (“Hangup”) and sigabbrev_np the abbreviation (“INT”); both return NULL for invalid signal numbers and point to storage that lives for the whole program (strsignal(3), manual Signal Messages).

Gotchas and portability

• strsignal keeps per-thread state but falls back to a shared static buffer if TSD allocation fails; the manual marks it mtasurace:strsignal and lists asucorrupt/ascuheap hazards (signal.texi Signal Messages safety block). Signal handlers should prefer the _np pair, which the manual marks plain MT-Safe/AS-safe.
• sigdescr_np/sigabbrev_np are glibc 2.32 additions (NEWS under Version 2.32: “sigdescr_np does not translate the returned string”), introduced to replace the deprecated sys_siglist array.
• sys_siglist is gone as a default symbol since glibc 2.32 (strsignal(3) VERSIONS cites glibc commit b1ccfc061feee9ce6); nm on this host confirms only non-default compat versions remain (sys_siglist@GLIBC_2.2.5, @GLIBC_2.3.3).
• Invalid signal numbers: strsignal returns an “unknown signal” message on Linux; some systems return NULL instead (strsignal(3) RETURN VALUE).
• psignal writes to stderr, so it is neither async-signal-safe nor suitable inside signal handlers that must not touch stdio (psignal(3) ATTRIBUTES: MT-Safe locale only).
• musl 1.2.5 provides strsignal (musl src/string/strsignal.c) but not the _np pair (absent from musl include/string.h).

References

• glibc manual: signal.texi, subsection Signal Messages
• man3: strsignal(3) (covers sigdescr_np, sigabbrev_np via .so alias sigdescr_np.3), psignal(3)
• headers: /usr/include/string.h, /usr/include/signal.h
• symbols: nm -D --with-symbol-versions libc.so.6