proc.5: Document /proc/sys/kernel/shm_rmid_forced

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

1 files changed, 36 insertions, 0 deletions

diff --git a/man5/proc.5 b/man5/proc.5
index e5632dcc..520c5fc8 100644
--- a/man5/proc.5
+++ b/man5/proc.5
@@ -2965,6 +2965,42 @@ the value of
 .BR SG_BIG_BUFF .
 However, there shouldn't be any reason to change this value.
 .TP
+.IR /proc/sys/kernel/shm_rmid_forced " (since Linux 3.1)"
+.\" commit b34a6b1da371ed8af1221459a18c67970f7e3d53
+.\" See also Documentation/sysctl/kernel.txt
+If this file is set to 1, all System V shared memory segments will
+be marked for destruction as soon as the number of attached processes
+falls to zero;
+in other words, it is no longer possible to create shared memory segments
+that exist independently of any attached process.
+.IP
+The effect is as though a
+.BR shmctl (2)
+.B IPC_RMID
+is performed on all existing  segments as well as all segments
+created in the future (until this file is reset to 0).
+Note that existing segments that are attached to no process will be
+immediately destroyed when this file is set to 1.
+Setting this option will also destroy segments that were created,
+but never attached,
+upon termination of the process that created the segment with
+.BR shmget (2).
+.IP
+Setting this file to 1 provides a way of ensuring that
+all System V shared memory segments are counted against the
+resource usage and resource limits (see the description of
+.B RLIMIT_AS
+in
+.BR getrlimit (2))
+of at least one process.
+.IP
+Because setting this file to 1 produces behavior that is nonstandard
+and could also break existing applications,
+the default value in this file is 0.
+Only set this file to 1 if you have a good understanding
+of the semantics of the applications using
+System V shared memory on your system.
+.TP
 .I /proc/sys/kernel/shmall
 This file
 contains the system-wide limit on the total number of pages of