man-pages/man2/getrlimit.2

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.\" Copyright (c) 1992 Drew Eckhardt, March 28, 1992
.\" Copyright (c) 2002 Michael Kerrisk
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.\" Modified by Michael Haardt <michael@moria.de>
.\" Modified 1993-07-23 by Rik Faith <faith@cs.unc.edu>
.\" Modified 1996-01-13 by Arnt Gulbrandsen <agulbra@troll.no>
.\" Modified 1996-01-22 by aeb, following a remark by
.\"          Tigran Aivazian <tigran@sco.com>
.\" Modified 1996-04-14 by aeb, following a remark by
.\"          Robert Bihlmeyer <robbe@orcus.ping.at>
.\" Modified 1996-10-22 by Eric S. Raymond <esr@thyrsus.com>
.\" Modified 2001-05-04 by aeb, following a remark by
.\"          H<>vard Lygre <hklygre@online.no>
.\" Modified 2001-04-17 by Michael Kerrisk <mtk-manpages@gmx.net>
.\" Modified 2002-06-13 by Michael Kerrisk <mtk-manpages@gmx.net>
.\"     Added note on non-standard behaviour when SIGCHLD is ignored.
.\" Modified 2002-07-09 by Michael Kerrisk <mtk-manpages@gmx.net>
.\"	Enhanced descriptions of 'resource' values for [gs]etrlimit()
.\" Modified 2003-11-28 by aeb, added RLIMIT_CORE
.\" Modified 2004-03-26 by aeb, added RLIMIT_AS
.\" Modified 2004-06-16 by Michael Kerrisk <mtk-manpages@gmx.net>
.\"     Added notes on CAP_SYS_RESOURCE
.\"
.TH GETRLIMIT 2 2004-06-16 "Linux" "Linux Programmer's Manual"
.SH NAME
getrlimit, getrusage, setrlimit \- get/set resource limits and usage
.SH SYNOPSIS
.B #include <sys/time.h>
.br
.B #include <sys/resource.h>
.br
.B #include <unistd.h>
.sp
.BI "int getrlimit(int " resource ", struct rlimit *" rlim );
.br
.BI "int getrusage(int " who ", struct rusage *" usage );
.br
.BI "int setrlimit(int " resource ", const struct rlimit *" rlim );
.SH DESCRIPTION
.B getrlimit
and
.B setrlimit
get and set resource limits respectively.
Each resource has an associated soft and hard limit, as defined by the 
.B rlimit
structure (the
.I rlim
argument to both
.BR getrlimit "() and " setrlimit ()):
.PP
.in +0.5i
.nf
struct rlimit {
    rlim_t rlim_cur;   /* Soft limit */
    rlim_t rlim_max;   /* Hard limit (ceiling 
                          for rlim_cur) */
};

.fi
.in -0.5i
The soft limit is the value that the kernel enforces for the
corresponding resource.
The hard limit acts as a ceiling for the soft limit:
an unprivileged process may only set its soft limit to a value in the 
range from 0 up to the hard limit, and (irreversibly) lower its hard limit.
A privileged process (under Linux: one with the
.B CAP_SYS_RESOURCE
capability) may make arbitrary changes to either limit value.
.PP
The value
.B RLIM_INFINITY
denotes no limit on a resource (both in the structure returned by
.BR getrlimit ()
and in the structure passed to
.BR setrlimit ()).
.PP
.I resource
must be one of:
.TP
.B RLIMIT_AS
The maximum size of the process's virtual memory (address space) in bytes.
.\" since 2.0.27 / 2.1.12
This limit affects calls to
.BR brk (2),
.BR mmap (2)
and
.BR mremap (2),
which fail with the error
.B ENOMEM
upon exceeding this limit. Also automatic stack expansion will fail
(and generate a SIGSEGV that kills the process when no alternate stack
has been made available).
Since the value is a long, on machines with a 32-bit long
either this limit is at most 2 GiB, or this resource is unlimited.
.TP
.B RLIMIT_CORE
Maximum size of
.I core
file. When 0 no core dump files are created.
When nonzero, larger dumps are truncated to this size.
.TP
.B RLIMIT_CPU
CPU time limit in seconds.
When the process reaches the soft limit, it is sent a
.B SIGXCPU
signal.
The default action for this signal is to terminate the process.
However, the signal can be caught, and the handler can return control to
the main program.
If the process continues to consume CPU time, it will be sent
.B SIGXCPU
once per second until the hard limit is reached, at which time
it is sent
.BR SIGKILL .
(This latter point describes Linux 2.2 and 2.4 behaviour.
Implementations vary in how they treat processes which continue to
consume CPU time after reaching the soft limit.
Portable applications that need to catch this signal should
perform an orderly termination upon first receipt of
.BR SIGXCPU .)
.TP
.B RLIMIT_DATA
The maximum size of the process's data segment (initialized data,
uninitialized data, and heap).
This limit affects calls to
.BR brk "() and " sbrk (),
which fail with the error
.B ENOMEM
upon encountering the soft limit of this resource.
.TP
.B RLIMIT_FSIZE
The maximum size of files that the process may create.
Attempts to extend a file beyond this limit result in delivery of a
.B SIGXFSZ
signal.
By default, this signal terminates a process, but a process can 
catch this signal instead, in which case the relevant system call (e.g., 
.BR write "(), " truncate ())
fails with the error
.BR EFBIG .
.TP
.B RLIMIT_LOCKS
A limit on the combined number of
.BR flock ()
locks and 
.BR fcntl()
leases that this process may establish.
(Early Linux 2.4 only.)
.\" to be precise: Linux 2.4.0-test9; no longer in 2.4.25 / 2.5.65
.TP
.B RLIMIT_MEMLOCK
The maximum number of bytes of virtual memory that may be locked
into RAM using
.BR mlock "() and " mlockall ().
.TP
.B RLIMIT_NOFILE
Specifies a value one greater than the maximum file descriptor number
that can be opened by this process.
Attempts
.RB ( open "(), " pipe "(), " dup "(), etc.)"
to exceed this limit yield the error
.BR EMFILE .
.TP
.B RLIMIT_NPROC
The maximum number of processes that can be created for the real user
ID of the calling process.
Upon encountering this limit, 
.BR fork ()
fails with the error
.BR EAGAIN .
.TP
.B RLIMIT_RSS
Specifies the limit (in pages) of the process's resident set
(the number of virtual pages resident in RAM).
This limit only has effect in Linux 2.4 onwatrds, and there only
affects calls to
.BR madvise ()
specifying
.BR MADVISE_WILLNEED .
.TP
.B RLIMIT_STACK
The maximum size of the process stack, in bytes.
Upon reaching this limit, a
.B SIGSEGV
signal is generated.
To handle this signal, a process must employ an alternate signal stack
.RB ( sigaltstack (2)).
.PP
.B RLIMIT_OFILE
is the BSD name for 
.BR RLIMIT_NOFILE .
.PP
.B getrusage
returns the current resource usages, for a \fIwho\fP
of either 
.B RUSAGE_SELF
or 
.BR RUSAGE_CHILDREN .
The former asks for resources used by the current process,
the latter for resources used by those of its children
that have terminated and have been waited for.
.PP 
.in +0.5i
.nf
struct rusage {
    struct timeval ru_utime; /* user time used */
    struct timeval ru_stime; /* system time used */
    long   ru_maxrss;        /* maximum resident set size */
    long   ru_ixrss;         /* integral shared memory size */
    long   ru_idrss;         /* integral unshared data size */
    long   ru_isrss;         /* integral unshared stack size */
    long   ru_minflt;        /* page reclaims */
    long   ru_majflt;        /* page faults */
    long   ru_nswap;         /* swaps */
    long   ru_inblock;       /* block input operations */
    long   ru_oublock;       /* block output operations */
    long   ru_msgsnd;        /* messages sent */
    long   ru_msgrcv;        /* messages received */
    long   ru_nsignals;      /* signals received */
    long   ru_nvcsw;         /* voluntary context switches */
    long   ru_nivcsw;        /* involuntary context switches */
};
.fi
.in -0.5i
.SH "RETURN VALUE"
On success, zero is returned.  On error, \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
.TP
.B EFAULT
.I rlim
or
.I usage
points outside the accessible address space.
.TP
.B EINVAL
.BR getrlimit " or " setrlimit
is called with a bad \fIresource\fP, or \fBgetrusage\fP is called with a
bad \fIwho\fP.
.TP
.B EPERM
An unprivileged process tried to use \fBsetrlimit()\fP to
increase a soft or hard limit above the current hard limit; the
.B CAP_SYS_RESOURCE
capability is required to do this.
Or, the process tried to use \fBsetrlimit()\fP to increase
the soft or hard RLIMIT_NOFILE limit above the current kernel
maximum (NR_OPEN).
.SH "CONFORMING TO"
SVr4, BSD 4.3
.SH NOTE
Including
.I <sys/time.h>
is not required these days, but increases portability.
(Indeed,
.I struct timeval
is defined in
.IR <sys/time.h> .)
.PP
On Linux, if the disposition of
.B SIGCHLD
is set to
.B SIG_IGN
then the resource usages of child processes
are automatically included in the value returned by
.BR RUSAGE_CHILDREN ,
although POSIX 1003.1-2001 explicitly prohibits this.
.\" See the description of getrusage() in XSH.
.\" A similar statement was also in SUSv2.
.LP
The above struct was taken from BSD 4.3 Reno.
Not all fields are meaningful under Linux.
Right now (Linux 2.4, 2.6) only the fields
.BR ru_utime ,
.BR ru_stime ,
.BR ru_minflt ,
.BR ru_majflt ,
and
.BR ru_nswap
are maintained.
.SH "SEE ALSO"
.BR dup (2),
.BR fcntl (2),
.BR fork (2),
.BR mlock (2),
.BR mlockall (2),
.BR mmap (2),
.BR open (2),
.BR quotactl (2),
.BR sbrk (2),
.BR wait3 (2),
.BR wait4 (2),
.BR malloc (3),
.BR ulimit (3),
.BR capabilities (7),
.BR signal (7)