getrlimit(2) getrlimit(2)
NAME
getrlimit, getrlimit64, setrlimit, setrlimit64 - control maximum system
resource consumption
SYNOPSIS
#include <sys/resource.h>
int getrlimit(int resource, struct rlimit *rlp);
int getrlimit64(int resource, struct rlimit64 *rlp);
int setrlimit(int resource, const struct rlimit *rlp);
int setrlimit64(int resource, const struct rlimit64 *rlp);
DESCRIPTION
Limits on the consumption of a variety of system resources by a process
and each process it creates may be obtained with getrlimit and set with
setrlimit.
getrlimit64 and setrlimit64 allow 32-bit programs to set 64-bit limits.
This is particularly useful for shells and other 32-bit programs which
fork 64-bit binaries. Unless otherwise specified, getrlimit64 and
setrlimit64 function in exactly the same manner as getrlimit and
setrlimit.
Each call to either getrlimit or setrlimit identifies a specific resource
to be operated upon as well as a resource limit. A resource limit is a
pair of values: one specifying the current (soft) limit, the other a
maximum (hard) limit. Soft limits may be changed by a process to any
value that is less than or equal to the hard limit. A process may
(irreversibly) lower its hard limit to any value that is greater than or
equal to the soft limit.
Only a the super-user can raise a hard limit.
Both hard and soft limits can be changed in a single call to setrlimit
subject to the constraints described above.
getrlimit64 and setrlimit64 are provided to allow 32 bit applications to
manipulate 64 bit limit values. For example, the RLIMIT_FSIZE can be set
as large as 0xffffffffff with setrlimit64 when using the xfs filesystem.
When using the 32 bit interfaces, limits may have an infinite value of
RLIM_INFINITY (0x7fffffff). In this case rlp is a pointer to struct
rlimit that includes the following members:
rlim_t rlim_cur; /* current (soft) limit */
rlim_t rlim_max; /* hard limit */
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getrlimit(2) getrlimit(2)
rlim_t is an arithmetic data type to which objects of type int, size_t,
and off_t can be cast without loss of information. Specifying the
RLIM_INFINITY value as the limit in a setrlimit call may allow the value
of the resource to exceed 0x7fffffff. This is because specifying
RLIM_INFINITY as the limit indicates to the system to use no limit other
than that imposed by the operating system. When getrlimit is used to
retrieve a limit which has a value greater than that which can be
represented by an rlim_t, the value returned is the maximum value
representable by an rlim_t. This value is currently UINT_MAX.
When using the 64 bit interfaces, limits may have an infinite value of
RLIM64_INFINITY (0x7fffffffffffffff). In this case rlp is a pointer to
struct rlimit64 that includes the following members:
rlim64_t rlim_cur;/* current (soft) limit */
rlim64_t rlim_max;/* hard limit */
rlim64_t is an arithmetic data type to which objects of type long long
and off64_t can be cast without loss of information.
The possible resources, their descriptions, and the actions taken when
current limit is exceeded, are summarized below:
RLIMIT_CORE The maximum size of a core file in bytes that may be
created by a process. A limit of 0 will prevent the
creation of a core file. The writing of a core file
will terminate at this size.
RLIMIT_CPU The maximum amount of CPU time in seconds used by a
process. SIGXCPU is sent to a process which exceeds
this limit. If the process is holding or ignoring
SIGXCPU, the behavior is scheduling class defined.
Unless the SVR4_SIGNALS variable in /etc/default/login
is set to NO, this signal will be ignored by default.
RLIMIT_DATA The maximum size of a process's heap in bytes. A brk(2)
which attempts to exceed this limit will fail with errno
set to ENOMEM.
RLIMIT_FSIZE The maximum size of a file in bytes that may be created
by a process. A limit of 0 will prevent the creation of
a file. A process which attempts to exceed this limit
will fail with errno set to SIGXFSZ. If the process is
holding or ignoring SIGXFSZ, continued attempts to
increase the size of a file beyond the limit will fail
with errno set to EFBIG. Unless the SVR4_SIGNALS
variable in /etc/default/login is set to NO, this signal
will be ignored by default.
RLIMIT_NOFILE The maximum number of open file descriptors that the
process can have. Functions that attempt to create new
file descriptors beyond this limit will fail with errno
set to EMFILE.
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getrlimit(2) getrlimit(2)
RLIMIT_STACK The maximum size of a process's stack in bytes. SIGSEGV
is sent to a process which attempts to exceed this
limit. If the process is holding or ignoring SIGSEGV,
or is catching SIGSEGV and has not made arrangements to
use an alternate stack [see sigaltstack(2)], the
disposition of SIGSEGV will be set to SIG_DFL before it
is sent. This value is used as the default stacksize by
sproc(2).
RLIMIT_VMEM The maximum size of a process's mapped address space in
bytes. brk(2) and mmap(2) functions which attempt to
exceed this limit will fail with errno set to ENOMEM.
In addition, the automatic stack growth will fail with
the effects outlined above.
RLIMIT_RSS The maximum size, in bytes to which a process's resident
set size may grow. This imposes a limit on the amount
of physical memory to be given to a process; if memory
is tight, the system will prefer to take memory from
processes that are exceeding their declared resident set
size.
RLIMIT_PTHREAD The maximum number of threads (pthreads(5)) that a
process may create. Functions that attempt to create
new threads beyond this limit will fail with the error
EAGAIN.
Because limit information is stored in the per-process information, the
shell builtin ulimit must directly execute this system call if it is to
affect all future processes created by the shell; limit is thus a built-
in command to sh(1) and csh(1).
The value of the current limit of the following resources affect these
implementation defined constants:
Limit Implementation Defined Constant
_______________________________________________
RLIMIT_NOFILE OPEN_MAX
RETURN VALUE
Upon successful completion, the function getrlimit returns a value of 0;
otherwise, it returns a value of -1 and sets errno to indicate an error.
ERRORS
Under the following conditions, the functions getrlimit and setrlimit
fail and set errno to:
[EFAULT] The address specified for rlp in invalid.
[EINVAL] if an invalid resource was specified; or in a setrlimit
call, the new rlim_cur exceeds the new rlim_max.
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getrlimit(2) getrlimit(2)
[EPERM] if the limit specified to setrlimit would have raised the
maximum limit value and the caller is not the super-user.
SEE ALSO
csh(1), sh(1), open(2), sigaltstack(2), malloc(3C), signal(5).
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