mirror of https://github.com/mkerrisk/man-pages
432 lines
13 KiB
Groff
432 lines
13 KiB
Groff
.\" Hey Emacs! This file is -*- nroff -*- source.
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.\"
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.\" Copyright (c) 1992 Drew Eckhardt, March 28, 1992
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.\" Copyright (c) 2002 Michael Kerrisk
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.\" Modified by Michael Haardt <michael@moria.de>
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.\" Modified 1993-07-23 by Rik Faith <faith@cs.unc.edu>
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.\" Modified 1996-01-13 by Arnt Gulbrandsen <agulbra@troll.no>
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.\" Modified 1996-01-22 by aeb, following a remark by
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.\" Tigran Aivazian <tigran@sco.com>
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.\" Modified 1996-04-14 by aeb, following a remark by
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.\" Robert Bihlmeyer <robbe@orcus.ping.at>
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.\" Modified 1996-10-22 by Eric S. Raymond <esr@thyrsus.com>
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.\" Modified 2001-05-04 by aeb, following a remark by
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.\" Håvard Lygre <hklygre@online.no>
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.\" Modified 2001-04-17 by Michael Kerrisk <mtk-manpages@gmx.net>
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.\" Modified 2002-06-13 by Michael Kerrisk <mtk-manpages@gmx.net>
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.\" Added note on non-standard behaviour when SIGCHLD is ignored.
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.\" Modified 2002-07-09 by Michael Kerrisk <mtk-manpages@gmx.net>
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.\" Enhanced descriptions of 'resource' values for [gs]etrlimit()
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.\" Modified 2003-11-28 by aeb, added RLIMIT_CORE
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.\" Modified 2004-03-26 by aeb, added RLIMIT_AS
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.\" Modified 2004-06-16 by Michael Kerrisk <mtk-manpages@gmx.net>
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.\" Added notes on CAP_SYS_RESOURCE
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.\"
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.\" 2004-11-16 -- mtk: the getrlimit.2 page, which formally included
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.\" coverage of getrusage(2), has been split, so that the latter
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.\" is now covered in its own getrusage.2.
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.\"
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.\" Modified 2004-11-16, mtk: A few other minor changes
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.\" Modified 2004-11-23, mtk
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.\" Added notes on RLIMIT_MEMLOCK, RLIMIT_NPROC, and RLIMIT_RSS
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.\" to "CONFORMING TO"
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.\" Modified 2004-11-25, mtk
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.\" Rewrote discussion on RLIMIT_MEMLOCK to incorporate kernel
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.\" 2.6.9 changes.
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.\" Added note on RLIMIT_CPU error in older kernels
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.\" 2004-11-03, mtk, Added RLIMIT_SIGPENDING
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.\" 2005-07-13, mtk, documented RLIMIT_MSGQUEUE limit.
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.\" 2005-07-28, mtk, Added descriptions of RLIMIT_NICE and RLIMIT_RTPRIO
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.\"
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.TH GETRLIMIT 2 2005-09-20 "Linux 2.6.13" "Linux Programmer's Manual"
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.SH NAME
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getrlimit, setrlimit \- get/set resource limits
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.SH SYNOPSIS
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.B #include <sys/time.h>
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.br
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.B #include <sys/resource.h>
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.sp
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.BI "int getrlimit(int " resource ", struct rlimit *" rlim );
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.br
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.BI "int setrlimit(int " resource ", const struct rlimit *" rlim );
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.SH DESCRIPTION
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.BR getrlimit ()
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and
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.BR setrlimit ()
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get and set resource limits respectively.
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Each resource has an associated soft and hard limit, as defined by the
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.I rlimit
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structure (the
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.I rlim
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argument to both
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.BR getrlimit ()
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and
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.BR setrlimit ()):
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.PP
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.in +0.5i
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.nf
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struct rlimit {
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rlim_t rlim_cur; /* Soft limit */
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rlim_t rlim_max; /* Hard limit (ceiling for rlim_cur) */
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};
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.fi
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.in -0.5i
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The soft limit is the value that the kernel enforces for the
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corresponding resource.
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The hard limit acts as a ceiling for the soft limit:
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an unprivileged process may only set its soft limit to a value in the
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range from 0 up to the hard limit, and (irreversibly) lower its hard limit.
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A privileged process (under Linux: one with the
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.B CAP_SYS_RESOURCE
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capability) may make arbitrary changes to either limit value.
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.PP
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The value
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.B RLIM_INFINITY
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denotes no limit on a resource (both in the structure returned by
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.BR getrlimit ()
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and in the structure passed to
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.BR setrlimit ()).
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.PP
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.I resource
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must be one of:
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.TP
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.B RLIMIT_AS
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The maximum size of the process's virtual memory (address space) in bytes.
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.\" since 2.0.27 / 2.1.12
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This limit affects calls to
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.BR brk (2),
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.BR mmap (2)
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and
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.BR mremap (2),
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which fail with the error
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.B ENOMEM
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upon exceeding this limit. Also automatic stack expansion will fail
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(and generate a
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.B SIGSEGV
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that kills the process if no alternate stack
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has been made available via
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.BR sigaltstack (2)).
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Since the value is a \fIlong\fP, on machines with a 32-bit \fIlong\fP
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either this limit is at most 2 GiB, or this resource is unlimited.
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.TP
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.B RLIMIT_CORE
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Maximum size of
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.I core
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file. When 0 no core dump files are created.
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When non-zero, larger dumps are truncated to this size.
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.TP
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.B RLIMIT_CPU
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CPU time limit in seconds.
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When the process reaches the soft limit, it is sent a
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.B SIGXCPU
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signal.
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The default action for this signal is to terminate the process.
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However, the signal can be caught, and the handler can return control to
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the main program.
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If the process continues to consume CPU time, it will be sent
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.B SIGXCPU
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once per second until the hard limit is reached, at which time
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it is sent
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.BR SIGKILL .
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(This latter point describes Linux 2.2 through 2.6 behaviour.
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Implementations vary in how they treat processes which continue to
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consume CPU time after reaching the soft limit.
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Portable applications that need to catch this signal should
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perform an orderly termination upon first receipt of
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.BR SIGXCPU .)
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.TP
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.B RLIMIT_DATA
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The maximum size of the process's data segment (initialized data,
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uninitialized data, and heap).
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This limit affects calls to
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.BR brk ()
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and
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.BR sbrk (),
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which fail with the error
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.B ENOMEM
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upon encountering the soft limit of this resource.
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.TP
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.B RLIMIT_FSIZE
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The maximum size of files that the process may create.
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Attempts to extend a file beyond this limit result in delivery of a
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.B SIGXFSZ
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signal.
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By default, this signal terminates a process, but a process can
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catch this signal instead, in which case the relevant system call (e.g.,
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.BR write ()
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.BR truncate ())
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fails with the error
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.BR EFBIG .
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.TP
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.BR RLIMIT_LOCKS " (Early Linux 2.4 only)"
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.\" to be precise: Linux 2.4.0-test9; no longer in 2.4.25 / 2.5.65
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A limit on the combined number of
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.BR flock ()
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locks and
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.BR fcntl ()
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leases that this process may establish.
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.TP
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.B RLIMIT_MEMLOCK
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The maximum number of bytes of memory that may be locked
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into RAM.
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In effect this limit is rounded down to the nearest multiple
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of the system page size.
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This limit affects
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.BR mlock (2)
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and
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.BR mlockall (2)
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and the
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.BR mmap (2)
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.B MAP_LOCKED
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operation.
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Since Linux 2.6.9 it also affects the
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.BR shmctl (2)
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.B SHM_LOCK
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operation, where it sets a maximum on the total bytes in
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shared memory segments (see
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.BR shmget (2))
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that may be locked by the real user ID of the calling process.
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The
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.BR shmctl (2)
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.B SHM_LOCK
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locks are accounted for separately from the per-process memory
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locks established by
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.BR mlock (2),
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.BR mlockall (2),
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and
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.BR mmap (2)
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.BR MAP_LOCKED ;
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a process can lock bytes up to this limit in each of these
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two categories.
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In Linux kernels before 2.6.9, this limit controlled the amount of
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memory that could be locked by a privileged process.
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Since Linux 2.6.9, no limits are placed on the amount of memory
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that a privileged process may lock, and this limit instead governs
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the amount of memory that an unprivileged process may lock.
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.TP
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.BR RLIMIT_MSGQUEUE " (Since Linux 2.6.8)"
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Specifies the limit on the number of bytes that can be allocated
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for POSIX message queues for the real user ID of the calling process.
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This limit is enforced for
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.BR mq_open (3).
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Each message queue that the user creates counts (until it is removed)
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against this limit according to the formula:
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.nf
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bytes = attr.mq_maxmsg * sizeof(struct msg_msg *) +
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attr.mq_maxmsg * attr.mq_msgsize
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.fi
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where
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.I attr
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is the
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.I mq_attr
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structure specified as the fourth argument to
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.BR mq_open ().
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The first addend in the formula, which includes
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.I "sizeof(struct msg_msg *)"
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(4 bytes on Linux/x86), ensures that the user cannot
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create an unlimited number of zero-length messages (such messages
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nevertheless each consume some system memory for bookkeeping overhead).
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.TP
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.BR RLIMIT_NICE " (since kernel 2.6.12, but see BUGS below)"
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Specifies a ceiling to which the process's nice value can be raised using
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.BR setpriority (2)
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or
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.BR nice (2).
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The actual ceiling for the nice value is calculated as
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.IR "20\ \-\ rlim_cur" .
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(This strangeness occurs because negative numbers cannot be specified
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as resource limit values, since they typically have special meanings.
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For example, RLIM_INFINITY typically is the same as \-1.)
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.TP
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.B RLIMIT_NOFILE
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Specifies a value one greater than the maximum file descriptor number
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that can be opened by this process.
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Attempts
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.RB ( open (),
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.BR pipe (),
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.BR dup (),
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etc.)
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to exceed this limit yield the error
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.BR EMFILE .
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.TP
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.B RLIMIT_NPROC
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The maximum number of processes that can be created for the real user
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ID of the calling process.
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Upon encountering this limit,
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.BR fork ()
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fails with the error
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.BR EAGAIN .
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.TP
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.B RLIMIT_RSS
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Specifies the limit (in pages) of the process's resident set
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(the number of virtual pages resident in RAM).
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This limit only has effect in Linux 2.4.x, x < 30, and there only
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affects calls to
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.BR madvise ()
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specifying
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.BR MADV_WILLNEED .
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.\" As at kernel 2.6.12, this limit still does nothing in 2.6 though
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.\" talk of making it do something has surfaced from time to time in LKML
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.\" -- MTK, Jul 05
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.TP
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.BR RLIMIT_RTPRIO " (Since Linux 2.6.12, but see BUGS)"
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Specifies a ceiling on the real-time priority that may be set for
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this process using
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.BR sched_setscheduler (2)
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and
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.BR sched_setparam (2).
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.TP
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.BR RLIMIT_SIGPENDING " (Since Linux 2.6.8)"
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Specifies the limit on the number of signals
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that may be queued for the real user ID of the calling process.
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Both standard and real-time signals are counted for the purpose of
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checking this limit.
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However, the limit is only enforced for
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.BR sigqueue (2);
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it is always possible to use
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.BR kill (2)
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to queue one instance of any of the signals that are not already
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queued to the process.
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.\" This replaces the /proc/sys/kernel/rtsig-max system-wide limit
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.\" that was present in kernels <= 2.6.7. MTK Dec 04
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.TP
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.B RLIMIT_STACK
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The maximum size of the process stack, in bytes.
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Upon reaching this limit, a
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.B SIGSEGV
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signal is generated.
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To handle this signal, a process must employ an alternate signal stack
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.RB ( sigaltstack (2)).
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.PP
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.B RLIMIT_OFILE
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is the BSD name for
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.BR RLIMIT_NOFILE .
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.SH "RETURN VALUE"
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On success, zero is returned. On error, \-1 is returned, and
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.I errno
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is set appropriately.
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.SH ERRORS
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.TP
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.B EFAULT
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.I rlim
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points outside the accessible address space.
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.TP
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.B EINVAL
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.I resource
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is not valid;
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or, for
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.BR setrlimit ():
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.IR rlim->rlim_cur
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was greater than
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.IR rlim->rlim_max .
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.TP
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.B EPERM
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An unprivileged process tried to use \fBsetrlimit\fP() to
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increase a soft or hard limit above the current hard limit; the
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.B CAP_SYS_RESOURCE
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capability is required to do this.
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Or, the process tried to use \fBsetrlimit\fP() to increase
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the soft or hard RLIMIT_NOFILE limit above the current kernel
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maximum (NR_OPEN).
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.SH BUGS
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In older Linux kernels, the
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.B SIGXCPU
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and
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.B SIGKILL
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signals delivered when a process encountered the soft and hard
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.B RLIMIT_CPU
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limits were delivered one (CPU) second later than they should have been.
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This was fixed in kernel 2.6.8.
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In 2.6.x kernels before 2.6.17, a
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.B RLIMIT_CPU
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limit of 0 is wrongly treated as "no limit" (like
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.BR RLIM_INFINITY ).
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.\" FIXME . The following change occurred in 2.6.17-rc1; verify
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.\" that it stays for 2.6.17 final.
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.\" see http://marc.theaimsgroup.com/?l=linux-kernel&m=114008066530167&w=2
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Since kernel 2.6.17, setting a limit of 0 does have an effect,
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but is actually treated as a limit of 1 second.
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A kernel bug means that
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.B RLIMIT_RTPRIO
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does not work in kernel 2.6.12; the problem is fixed in kernel 2.6.13.
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In kernel 2.6.12, there was an off-by-one mismatch
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between the priority ranges returned by
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.BR getpriority (2)
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and
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.BR RLIMIT_NICE .
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This had the effect that actual ceiling for the nice value
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was calculated as
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.IR "19\ \-\ rlim_cur" .
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This was fixed in kernel 2.6.13.
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.\" see http://marc.theaimsgroup.com/?l=linux-kernel&m=112256338703880&w=2
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Kernels before 2.4.22 did not diagnose the error
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.B EINVAL
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for
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.BR setrlimit ()
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when
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.IR rlim->rlim_cur
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was greater than
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.IR rlim->rlim_max .
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.SH "CONFORMING TO"
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SVr4, 4.3BSD.
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.BR RLIMIT_MEMLOCK
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and
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.BR RLIMIT_NPROC
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derive from BSD and are not specified in POSIX.1-2001;
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they are present on the BSDs and Linux, but on few other implementations.
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.BR RLIMIT_RSS
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derives from BSD and is not specified in POSIX.1-2001;
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it is nevertheless present on most implementations.
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.BR RLIMIT_MSGQUEUE ,
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.BR RLIMIT_NICE ,
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.BR RLIMIT_RTPRIO ,
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and
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.B RLIMIT_SIGPENDING
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are Linux specific.
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.SH "SEE ALSO"
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.BR dup (2),
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.BR fcntl (2),
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.BR fork (2),
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.BR getrusage (2),
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.BR mlock (2),
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.BR mmap (2),
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.BR open (2),
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.BR quotactl (2),
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.BR sbrk (2),
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.BR shmctl (2),
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.BR sigqueue (2),
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.BR malloc (3),
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.BR ulimit (3),
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.BR core (5),
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.BR capabilities (7),
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.BR signal (7)
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