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sem_overview.7: Fix discussion of length of semaphore names 

Because of the "sem." prefix added by glibc to a semaphore
name, the limit on the length of the name (excluding the
terminating null byte) is 251 characters.

Reported-by: Jens Thoms Toerring <jt@toerring.de>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2009-02-25 12:45:34 +13:00
parent 590d0346d9
commit 13e0f2a9d3
1 changed files with 8 additions and 3 deletions
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11
man7/sem_overview.7
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@ -23,7 +23,7 @@
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\"
.TH SEM_OVERVIEW 7 2009-02-20 "Linux" "Linux Programmer's Manual"
.TH SEM_OVERVIEW 7 2009-02-25 "Linux" "Linux Programmer's Manual"
.SH NAME
sem_overview \- Overview of POSIX semaphores
.SH DESCRIPTION
@ -46,8 +46,8 @@ unnamed semaphores.
A named semaphore is identified by a name of the form
.IR /somename ;
that is, a null-terminated string of up to
.BI NAME_MAX +1
(i.e., 256) characters consisting of an initial slash,
.BI NAME_MAX \-4
(i.e., 251) characters consisting of an initial slash,
.\" glibc allows the initial slash to be omitted, and makes
.\" multiple initial slashes equivalent to a single slash.
.\" This differs from the implementation of POSIX message queues.
@ -127,6 +127,11 @@ normally mounted under
.IR /dev/shm ,
with names of the form
.IR \fBsem.\fPsomename .
(This is the reason that semaphore names are limited to
.BI NAME_MAX \-4
rather than
.B NAME_MAX
characters.)
Since Linux 2.6.19, ACLs can be placed on files under this directory,
to control object permissions on a per-user and per-group basis.