* Alejandro Colomar [off-list ref], 2021-02-20, 11:05:

In the Linux kernel, there's only one system call, and it's called 
exit (its entry point is sys_exit(), and can be called using 
syscall(SYS_exit, ...) *but don't*), BUT it implements the 
functionality of _exit() (as the standards call it; see above).

To clarify, that's how it used to be, but since 2002ish there's also 
sys_exit_group, and glibc's _exit() uses that.

BTW, the exit_group.2 man page could use an update (possibly by merging 
it into exit.2): it says that the "system call is is equivalent to 
_exit(2) except that it terminates not only the calling thread, but all 
threads in the calling process’s thread group", which isn't helpful 
these days.

-- 
Jakub Wilk