239 lines
7.4 KiB
Groff
239 lines
7.4 KiB
Groff
.\" Copyright (c) 1980, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)getrlimit.2 8.1 (Berkeley) 6/4/93
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.\" $FreeBSD$
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.\"
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.Dd September 30, 2016
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.Dt GETRLIMIT 2
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.Os
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.Sh NAME
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.Nm getrlimit ,
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.Nm setrlimit
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.Nd control maximum system resource consumption
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/types.h
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.In sys/time.h
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.In sys/resource.h
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.Ft int
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.Fn getrlimit "int resource" "struct rlimit *rlp"
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.Ft int
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.Fn setrlimit "int resource" "const struct rlimit *rlp"
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.Sh DESCRIPTION
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Limits on the consumption of system resources by the current process
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and each process it creates may be obtained with the
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.Fn getrlimit
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system call, and set with the
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.Fn setrlimit
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system call.
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.Pp
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The
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.Fa resource
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argument is one of the following:
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.Bl -tag -width RLIMIT_FSIZEAA
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.It Dv RLIMIT_AS
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The maximum amount (in bytes) of virtual memory the process is
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allowed to map.
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.It Dv RLIMIT_CORE
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The largest size (in bytes)
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.Xr core 5
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file that may be created.
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.It Dv RLIMIT_CPU
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The maximum amount of cpu time (in seconds) to be used by
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each process.
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.It Dv RLIMIT_DATA
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The maximum size (in bytes) of the data segment for a process;
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this defines how far a program may extend its break with the
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.Xr sbrk 2
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function.
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.It Dv RLIMIT_FSIZE
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The largest size (in bytes) file that may be created.
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.It Dv RLIMIT_KQUEUES
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The maximum number of kqueues this user id is allowed to create.
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.It Dv RLIMIT_MEMLOCK
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The maximum size (in bytes) which a process may lock into memory
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using the
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.Xr mlock 2
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system call.
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.It Dv RLIMIT_NOFILE
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The maximum number of open files for this process.
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.It Dv RLIMIT_NPROC
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The maximum number of simultaneous processes for this user id.
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.It Dv RLIMIT_NPTS
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The maximum number of pseudo-terminals this user id is allowed to create.
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.It Dv RLIMIT_RSS
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When there is memory pressure and swap is available, prioritize eviction of
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a process' resident pages beyond this amount (in bytes).
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When memory is not under pressure, this rlimit is effectively ignored.
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Even when there is memory pressure, the amount of available swap space and some
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sysctl settings like
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.Xr vm.swap_enabled
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and
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.Xr vm.swap_idle_enabled
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can affect what happens to processes that have exceeded this size.
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.Pp
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Processes that exceed their set
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.Dv RLIMIT_RSS
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are not signalled or halted.
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The limit is merely a hint to the VM daemon to prefer to deactivate pages from
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processes that have exceeded their set
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.Dv RLIMIT_RSS .
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.It Dv RLIMIT_SBSIZE
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The maximum size (in bytes) of socket buffer usage for this user.
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This limits the amount of network memory, and hence the amount of
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mbufs, that this user may hold at any time.
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.It Dv RLIMIT_STACK
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The maximum size (in bytes) of the stack segment for a process;
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this defines how far a program's stack segment may be extended.
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Stack extension is performed automatically by the system.
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.It Dv RLIMIT_SWAP
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The maximum size (in bytes) of the swap space that may be reserved or
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used by all of this user id's processes.
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This limit is enforced only if bit 1 of the
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.Va vm.overcommit
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sysctl is set.
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Please see
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.Xr tuning 7
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for a complete description of this sysctl.
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.It Dv RLIMIT_VMEM
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An alias for
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.Dv RLIMIT_AS .
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.El
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.Pp
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A resource limit is specified as a soft limit and a hard limit.
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When a soft limit is exceeded, a process might or might not receive a signal.
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For example, signals are generated when the cpu time or file size is exceeded,
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but not if the address space or RSS limit is exceeded.
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A program that exceeds the soft limit is allowed to continue execution until it
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reaches the hard limit, or modifies its own resource limit.
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Even reaching the hard limit does not necessarily halt a process.
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For example, if the RSS hard limit is exceeded, nothing happens.
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.Pp
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The
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.Vt rlimit
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structure is used to specify the hard and soft limits on a resource.
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.Bd -literal -offset indent
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struct rlimit {
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rlim_t rlim_cur; /* current (soft) limit */
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rlim_t rlim_max; /* maximum value for rlim_cur */
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};
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.Ed
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.Pp
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Only the super-user may raise the maximum limits.
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Other users
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may only alter
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.Fa rlim_cur
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within the range from 0 to
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.Fa rlim_max
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or (irreversibly) lower
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.Fa rlim_max .
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.Pp
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An
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.Dq infinite
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value for a limit is defined as
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.Dv RLIM_INFINITY .
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.Pp
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Because this information is stored in the per-process information,
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this system call must be executed directly by the shell if it
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is to affect all future processes created by the shell;
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.Ic limit
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is thus a built-in command to
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.Xr csh 1 .
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.Pp
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The system refuses to extend the data or stack space when the limits
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would be exceeded in the normal way: a
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.Xr brk 2
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function fails if the data space limit is reached.
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When the stack limit is reached, the process receives
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a segmentation fault
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.Pq Dv SIGSEGV ;
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if this signal is not
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caught by a handler using the signal stack, this signal
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will kill the process.
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.Pp
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A file I/O operation that would create a file larger that the process'
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soft limit will cause the write to fail and a signal
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.Dv SIGXFSZ
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to be
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generated; this normally terminates the process, but may be caught.
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When
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the soft cpu time limit is exceeded, a
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.Dv SIGXCPU
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signal is sent to the
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offending process.
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.Pp
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When most operations would allocate more virtual memory than allowed by the
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soft limit of
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.Dv RLIMIT_AS ,
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the operation fails with
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.Dv ENOMEM
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and no signal is raised.
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A notable exception is stack extension, described above.
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If stack extension would allocate more virtual memory than allowed by the soft
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limit of
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.Dv RLIMIT_AS ,
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a
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.Dv SIGSEGV
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signal will be delivered.
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The caller is free to raise the soft address space limit up to the hard limit
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and retry the allocation.
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.Sh RETURN VALUES
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.Rv -std
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.Sh ERRORS
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The
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.Fn getrlimit
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and
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.Fn setrlimit
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system calls
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EFAULT
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The address specified for
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.Fa rlp
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is invalid.
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.It Bq Er EPERM
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The limit specified to
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.Fn setrlimit
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would have
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raised the maximum limit value, and the caller is not the super-user.
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.El
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.Sh SEE ALSO
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.Xr csh 1 ,
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.Xr quota 1 ,
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.Xr quotactl 2 ,
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.Xr sigaction 2 ,
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.Xr sigaltstack 2 ,
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.Xr sysctl 3 ,
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.Xr ulimit 3
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.Sh HISTORY
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The
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.Fn getrlimit
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system call appeared in
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.Bx 4.2 .
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