08-26-2001
limits on array sizes
The answer is No and Yes. Theoretically,
there is no limit. However, the kernel may be
configured to allow only a limited amount
of memory per process and/or user. You can find
out what the system resource limits are on your
particular UNIX system using the system
call "getrlimit()" (man section 2). The following
C program can be compiled and run as any ordinary
user...
================== SNIP ========================
/*
* Filename - getlimits.c
*
* Description - display system resource limits and
* test allocating large blocks of memory.
*
*/
#include <sys/time.h>
#include <sys/resource.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
main(int argc, char **argv)
{
struct rlimit rlim;
void *p;
getrlimit(RLIMIT_CPU, &rlim);
printf("CPU: cur - %ld max - %ld\n", rlim.rlim_cur, rlim.rlim_max);
getrlimit(RLIMIT_FSIZE, &rlim);
printf("FSIZE: cur - %ld max - %ld\n", rlim.rlim_cur, rlim.rlim_max);
getrlimit(RLIMIT_DATA, &rlim);
printf("DATA: cur - %ld max - %ld\n", rlim.rlim_cur, rlim.rlim_max);
getrlimit(RLIMIT_STACK, &rlim);
printf("STACK: cur - %ld max - %ld\n", rlim.rlim_cur, rlim.rlim_max);
getrlimit(RLIMIT_CORE, &rlim);
printf("CORE: cur - %ld max - %ld\n", rlim.rlim_cur, rlim.rlim_max);
#ifdef LINUX
getrlimit(RLIMIT_RSS, &rlim);
printf("RSS: cur - %ld max - %ld\n", rlim.rlim_cur, rlim.rlim_max);
getrlimit(RLIMIT_NPROC, &rlim);
printf("NPROC: cur - %ld max - %ld\n", rlim.rlim_cur, rlim.rlim_max);
#else
getrlimit(RLIMIT_VMEM, &rlim);
printf("VMEM: cur - %ld max - %ld\n", rlim.rlim_cur, rlim.rlim_max);
getrlimit(RLIMIT_AS, &rlim);
printf("AS: cur - %ld max - %ld\n", rlim.rlim_cur, rlim.rlim_max);
#endif
getrlimit(RLIMIT_NOFILE, &rlim);
printf("NOFILE: cur - %ld max - %ld\n", rlim.rlim_cur, rlim.rlim_max);
#ifdef LINUX
getrlimit(RLIMIT_MEMLOCK, &rlim);
printf("MEMLOCK: cur - %ld max - %ld\n", rlim.rlim_cur, rlim.rlim_max);
#endif
if((p = malloc(100000000)) == NULL)
{
printf("malloc 100M failed\n");
}
else
{
printf("malloc 100M succeeded\n");
}
if(p) free(p);
if((p = malloc(500000000)) == NULL)
{
printf("malloc 500M failed\n");
}
else
{
printf("malloc 500M succeeded\n");
}
if(p) free(p);
return 0;
}
================== SNIP ========================
The output (on Linux) should look somthing like...
$ getlimits
CPU: cur - 2147483647 max - 2147483647
FSIZE: cur - 2147483647 max - 2147483647
DATA: cur - 2147483647 max - 2147483647
STACK: cur - 8388608 max - 2147483647
CORE: cur - 1024000000 max - 2147483647
RSS: cur - 2147483647 max - 2147483647
NPROC: cur - 2048 max - 2048
NOFILE: cur - 1024 max - 1024
MEMLOCK: cur - 2147483647 max - 2147483647
malloc 100M succeeded
malloc 500M succeeded
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LEARN ABOUT ULTRIX
setrlimit
getrlimit(2) System Calls Manual getrlimit(2)
Name
getrlimit, setrlimit - control maximum system resource consumption
Syntax
#include <sys/time.h>
#include <sys/resource.h>
getrlimit(resource, rlp)
int resource;
struct rlimit *rlp;
setrlimit(resource, rlp)
int resource;
struct rlimit *rlp;
Description
Limits on the consumption of system resources by the current process and each process it creates can be obtained with the call and set with
the call.
The resource parameter is one of the following:
RLIMIT_CPU the maximum amount of cpu time (in milliseconds) to be used by each process.
RLIMIT_FSIZE the largest size, in bytes, of any single file that may be created.
RLIMIT_DATA the maximum size, in bytes, of the data segment for a process. This limit defines how far a program can extend its break
with the system call.
RLIMIT_STACK the maximum size, in bytes, of the stack segment for a process. This limit defines how far a program's stack segment can
be extended, either automatically by the system or explicitly by a user, with the system call.
RLIMIT_CORE the largest size, in bytes, of a core file that may be created.
RLIMIT_RSS the maximum size, in bytes, to which a process's resident set size may grow when there is a shortage of free physical mem-
ory. Exceeding this limit when free physical memory is in short supply results in an unfavorable scheduling priority
being assigned to the process.
A resource limit is specified as a soft limit and a hard limit. When a soft limit is exceeded, a process may receive a signal (for exam-
ple, if the cpu time is exceeded), but it will be allowed to continue execution until it reaches the hard limit (or modifies its resource
limit). The system uses just the soft limit field of the resources RLIMIT_CORE and RLIMIT_RSS. The rlimit structure is used to specify the
hard and soft limits on a resource, as shown:
struct rlimit {
int rlim_cur; /* current (soft) limit */
int rlim_max; /* hard limit */
};
Only the superuser may raise the maximum limits. Other users may alter rlim_cur within the range from 0 to rlim_max or (irreversibly)
lower rlim_max.
An "infinite" value for a limit is defined as RLIM_INFINITY (0x7fffffff).
Because this information is stored in the per-process information, this system call must be executed directly by the shell if it is to
affect all future processes created by the shell; limit is thus a built-in command to
The system refuses to extend the data or stack space when the limits would be exceeded in the normal way: a break call fails if the data
space limit is reached, or the process is killed when the stack limit is reached. Because the stack cannot be extended, there is no way to
send a signal.
A file I/O operation that creates too large a file causes the SIGXFSZ signal to be generated. This condition normally terminates the
process, but may be caught. When the soft cpu time limit is exceeded, a signal SIGXCPU is sent to the process.
Return Values
A 0 return value indicates that the call succeeded, changing or returning the resource limit. A return value of -1 indicates that an
error occurred, and an error code is stored in the global location errno.
Environment
System Five
When your program is compiled in the System V environment, the SIGXFSZ signal is not generated.
Diagnostics
The call fails under the following conditions:
[EFAULT] The address specified for rlp is invalid.
[EPERM] The limit specified to would have raised the maximum limit value, and the caller is not the superuser.
[EINVAL] Resource is greater than or equal to RLIM_NLIMITS.
See Also
csh(1), quota(2)
getrlimit(2)