BSD_SIGNAL(3) Linux Programmer's Manual BSD_SIGNAL(3)

bsd_signal - signal handling with BSD semantics

#include <signal.h>
typedef void (*sighandler_t)(int);
sighandler_t bsd_signal(int signum, sighandler_t handler);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
Since glibc 2.26:
&& ! (_POSIX_C_SOURCE >= 200809L)
Glibc 2.25 and earlier:

The bsd_signal() function takes the same arguments, and performs the same task, as signal(2).
The difference between the two is that bsd_signal() is guaranteed to provide reliable signal semantics, that is: a) the disposition of the signal is not reset to the default when the handler is invoked; b) delivery of further instances of the signal is blocked while the signal handler is executing; and c) if the handler interrupts a blocking system call, then the system call is automatically restarted. A portable application cannot rely on signal(2) to provide these guarantees.

The bsd_signal() function returns the previous value of the signal handler, or SIG_ERR on error.

As for signal(2).

For an explanation of the terms used in this section, see attributes(7).
Interface Attribute Value
bsd_signal () Thread safety MT-Safe

4.2BSD, POSIX.1-2001. POSIX.1-2008 removes the specification of bsd_signal(), recommending the use of sigaction(2) instead.

Use of bsd_signal() should be avoided; use sigaction(2) instead.
On modern Linux systems, bsd_signal() and signal(2) are equivalent. But on older systems, signal(2) provided unreliable signal semantics; see signal(2) for details.
The use of sighandler_t is a GNU extension; this type is defined only if the _GNU_SOURCE feature test macro is defined.

sigaction(2), signal(2), sysv_signal(3), signal(7)