222 lines
6.4 KiB
Groff
222 lines
6.4 KiB
Groff
.\" $NetBSD: getrlimit.2,v 1.26 2003/08/07 16:43:59 agc Exp $
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.\"
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.\" 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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.\" 3. 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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.\"
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.Dd November 23, 2001
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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/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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call, and set with the
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.Fn setrlimit
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call.
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Resources of an arbitrary process can be obtained/changed using
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.Xr sysctl 3 .
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..
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.Pp
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The
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.Fa resource
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parameter is one of the following:
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.Bl -tag -width RLIMIT_FSIZEAA
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.It Li RLIMIT_CORE
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The largest size (in bytes)
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.Pa core
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file that may be created.
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.It Li 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 Li 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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system call.
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.It Li RLIMIT_FSIZE
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The largest size (in bytes) file that may be created.
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.It Li 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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function.
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.It Li RLIMIT_NOFILE
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The maximum number of open files for this process.
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.It Li RLIMIT_NPROC
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The maximum number of simultaneous processes for this user id.
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.It Li RLIMIT_RSS
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The maximum size (in bytes) to which a process's resident set size may
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grow.
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This imposes a limit on the amount of physical memory to be given to
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a process; if memory is tight, the system will prefer to take memory
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from processes that are exceeding their declared resident set size.
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.It Li 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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.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 may receive a signal (for example,
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if the CPU time or file size is exceeded), but it will be allowed to
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continue execution until it reaches the hard limit (or modifies
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its resource limit).
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The
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.Em 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; /* hard limit */
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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 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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Thus, shells provide built-in commands to change the limits
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.Ic ( limit
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for
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.Xr csh 1 ,
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or
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.Ic ulimit
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for
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.Xr sh 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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call 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 the soft CPU time limit is exceeded, a signal
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.Dv SIGXCPU
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is sent to the
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offending process.
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.Sh RETURN VALUES
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A 0 return value indicates that the call succeeded, changing
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or returning the resource limit.
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Otherwise, -1 is returned and the global variable
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.Va errno
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is set to indicate the error.
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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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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 EINVAL
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Specified
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.Fa resource
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was invalid.
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.It Bq Er EINVAL
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In the
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.Fn setrlimit
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call, the specified
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.Fa rlim_cur
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exceeds the specified
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.Fa rlim_max .
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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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.Pp
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The
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.Fn setrlimit
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function may fail if:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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The limit specified to
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.Fn setrlimit
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cannot be lowered, because current usage is already higher than the limit.
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.El
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.Sh SEE ALSO
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.Xr csh 1 ,
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.Xr sh 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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.\" Sh STANDARDS
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.\" With exception of
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.\" .Li RLIMIT_AS
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.\" (which is not currently supported), the
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.\" .Fn getrlimit
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.\" and
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.\" .Fn setrlimit
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.\" functions conform to
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.\" .St -susv2 .
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.Sh HISTORY
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The
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.Fn getrlimit
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function call appeared in
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.Bx 4.2 .
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