git: bb14ba3777bb - main - daemon(3): Note about environment after calling daemon()

The branch main has been updated by obiwac:

URL: https://cgit.FreeBSD.org/src/commit/?id=bb14ba3777bb201abd6d4dfbf67d70b81f9c1e97

commit bb14ba3777bb201abd6d4dfbf67d70b81f9c1e97
Author:     Aymeric Wibo <obiwac@FreeBSD.org>
AuthorDate: 2026-06-17 19:51:39 +0000
Commit:     Aymeric Wibo <obiwac@FreeBSD.org>
CommitDate: 2026-06-17 22:44:46 +0000

    daemon(3): Note about environment after calling daemon()
    
    While here, fix missing comma typo.
    
    Reviewed by:    0mp, ziaee
    Approved by:    0mp, ziaee
    MFC after:      3 days
    Obtained from:  https://github.com/apple-oss-distributions/libc (partially)
    Sponsored by:   Klara, Inc.
    Differential Revision:  https://reviews.freebsd.org/D57384
---
 lib/libc/gen/daemon.3 | 26 ++++++++++++++++++++++++--
 1 file changed, 24 insertions(+), 2 deletions(-)

diff --git a/lib/libc/gen/daemon.3 b/lib/libc/gen/daemon.3
index 4619ba3489aa..99a4f685bedb 100644
--- a/lib/libc/gen/daemon.3
+++ b/lib/libc/gen/daemon.3
@@ -25,7 +25,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd February 27, 2023
+.Dd June 1, 2026
 .Dt DAEMON 3
 .Os
 .Sh NAME
@@ -44,6 +44,13 @@ The
 .Fn daemon
 function is for programs wishing to detach themselves from the
 controlling terminal and run in the background as system daemons.
+The
+.Xr fork 2
+system call is used; see
+.Sx CAVEATS
+below about the environment after a
+.Fn fork
+.Pq without a corresponding call to one of the exec routines .
 .Pp
 If the argument
 .Fa nochdir
@@ -89,7 +96,7 @@ and
 function may fail and set
 .Va errno
 for any of the errors specified for the library functions
-.Xr fork 2
+.Xr fork 2 ,
 .Xr open 2 ,
 and
 .Xr setsid 2 .
@@ -107,6 +114,21 @@ The
 function first appeared in
 .Fx 12.0 .
 .Sh CAVEATS
+In multithreaded programs, the child process after
+.Fn fork
+inherits copies of all mutexes and other synchronization state, but only the
+calling thread survives.
+Any locks held by other threads at the time of the call will remain permanently
+acquired in the child, causing deadlocks in any code that attempts to
+acquire them.
+Until one of the
+.Xr exec 3
+functions is called, the child should restrict itself to async-signal safe
+operations
+.Po see
+.Xr sigaction 2
+.Pc .
+.Pp
 Unless the
 .Fa noclose
 argument is non-zero,