system(3): Clarify return values

Our manual page currently states that system() will return 127 if it
fails to execute the shell.  The actual return value is, to quote POSIX,
“as if the command language interpreter had terminated using exit(127)
or _exit(127)”.

MFC after:	1 week
Sponsored by:	Klara, Inc.
Reviewed by:	bnovkov, kevans
Differential Revision:	https://reviews.freebsd.org/D55483

1 files changed, 5 insertions, 3 deletions

diff --git a/lib/libc/stdlib/system.3 b/lib/libc/stdlib/system.3
index 119432342f70..f09577099a5c 100644
--- a/lib/libc/stdlib/system.3
+++ b/lib/libc/stdlib/system.3
@@ -29,7 +29,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd January 11, 2024
+.Dd February 24, 2026
 .Dt SYSTEM 3
 .Os
 .Sh NAME
@@ -77,8 +77,10 @@ or \-1 if an error occurred when invoking
 .Xr fork 2
 or
 .Xr waitpid 2 .
-A return value of 127 means the execution of the shell
-failed.
+If the child process fails to execute the shell, it will terminate
+with an exit code of 127 and
+.Nm
+will return the corresponding exit status.
 .Sh SEE ALSO
 .Xr sh 1 ,
 .Xr execve 2 ,