Date: Wed, 17 Jun 2026 22:45:35 +0000 From: Aymeric Wibo <obiwac@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: bb14ba3777bb - main - daemon(3): Note about environment after calling daemon() Message-ID: <6a33238f.47105.567c52b0@gitrepo.freebsd.org>
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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,home | help
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