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getrlimit.2: Document Linux's nonstandard treatment or RLIMIT_CPU soft limit 

Upon encountering the RLIMIT_CPU soft limit when a SIGXCPU handler
has been installed, Linux invokes the signal handler *and* raises
the soft limit by one second. This behavior repeats until the
limit is encountered.  No other implementation that I tested
(Solaris 10, FreeBSD 9.0, OpenBSD 5.0) does this, and it seems
unlikely to be POSIX-conformant. The (Linux-specific)
RLIMIT_RTTIME soft limit exhibits similar behavior.

Reported-by: Trevor Woerner <twoerner@gmail.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2012-11-25 09:34:51 +01:00
parent e1282f176c
commit 27bada1fa1
1 changed files with 28 additions and 1 deletions
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29
man2/getrlimit.2
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@ -61,7 +61,7 @@
.\" 2008-05-07, mtk / Peter Zijlstra, Added description of RLIMIT_RTTIME
.\" 2010-11-06, mtk: Added documentation of prlimit()
.\"
.TH GETRLIMIT 2 2012-11-24 "Linux" "Linux Programmer's Manual"
.TH GETRLIMIT 2 2012-11-25 "Linux" "Linux Programmer's Manual"
.SH NAME
getrlimit, setrlimit, prlimit \- get/set resource limits
.SH SYNOPSIS
@ -614,6 +614,33 @@ was calculated as
This was fixed in kernel 2.6.13.
.\" see http://marc.theaimsgroup.com/?l=linux-kernel&m=112256338703880&w=2
Since Linux 2.6.12,
.\" The relevant patch, sent to LKML, seems to be
.\" http://thread.gmane.org/gmane.linux.kernel/273462
.\" From: Roland McGrath <roland <at> redhat.com>
.\" Subject: [PATCH 7/7] make RLIMIT_CPU/SIGXCPU per-process
.\" Date: 2005-01-23 23:27:46 GMT
if a process reaches its soft
.BR RLIMIT_CPU
limit and has a handler installed for
.BR SIGXCPU ,
then, in addition to invoking the signal handler,
the kernel increases the soft limit by one second.
This behavior repeats if the process continues to consume CPU time,
until the hard limit is reached,
at which point the process is killed.
Other implementations
.\" Tested Solaris 10, FreeBSD 9, OpenBSD 5.0
do not change the
.BR RLIMIT_CPU
soft limit in this manner,
and the Linux behavior is probably not standards conformant;
portable applications should avoid relying on this Linux-specific behavior.
.\" FIXME https://bugzilla.kernel.org/show_bug.cgi?id=50951
The Linux-specific
.BR RLIMIT_RTTIME
limit exhibits the same behavior when the soft limit is encountered.
Kernels before 2.4.22 did not diagnose the error
.B EINVAL
for