illumos: manual page: getrlimit.2

GETRLIMIT(2) System Calls GETRLIMIT(2)

NAME

getrlimit, setrlimit - control maximum system resource consumption

SYNOPSIS

#include <sys/resource.h>

int getrlimit(int resource, struct rlimit *rlp);

int setrlimit(int resource, const struct rlimit *rlp);

DESCRIPTION

Limits on the consumption of a variety of system resources by a process
and each process it creates may be obtained with the getrlimit() and set
with setrlimit() functions.

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 process with {PRIV_SYS_RESOURCE} asserted
in the effective set 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. Limits may have an "infinite" value of RLIM_INFINITY.
The rlp argument is a pointer to struct rlimit that includes the
following members:

rlim_t rlim_cur; /* current (soft) limit */
rlim_t rlim_max; /* hard limit */

The type 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.

The possible resources, their descriptions, and the actions taken when
the current limit is exceeded are summarized as follows:

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. This is a soft limit only. The SIGXCPU signal
is sent to the process. If the process is holding or
ignoring SIGXCPU, the behavior is scheduling class
defined.

RLIMIT_DATA
The maximum size of a process's heap in bytes. The
brk(2) function 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. The SIGXFSZ signal is sent to the process. 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.

RLIMIT_NOFILE
One more than the maximum value that the system may
assign to a newly created descriptor. This limit
constrains the number of file descriptors that a process
may create.

RLIMIT_STACK
The maximum size of a process's stack in bytes. The
system will not automatically grow the stack beyond this
limit.

Within a process, setrlimit() will increase the limit on
the size of your stack, but will not move current memory
segments to allow for that growth. To guarantee that the
process stack can grow to the limit, the limit must be
altered prior to the execution of the process in which
the new stack size is to be used.

Within a multithreaded process, setrlimit() has no
impact on the stack size limit for the calling thread if
the calling thread is not the main thread. A call to
setrlimit() for RLIMIT_STACK impacts only the main
thread's stack, and should be made only from the main
thread, if at all.

The SIGSEGV signal is sent to the process. 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.

RLIMIT_VMEM
The maximum size of a process's mapped address space in
bytes. If this limit is exceeded, the brk(2) and
mmap(2) functions will fail with errno set to ENOMEM.
In addition, the automatic stack growth will fail with
the effects outlined above.

RLIMIT_AS
This is the maximum size of a process's total available
memory, in bytes. If this limit is exceeded, the
brk(2), malloc(3C), mmap(2) and sbrk(2) functions will
fail with errno set to ENOMEM. In addition, the
automatic stack growth will fail with the effects
outlined above.

Because limit information is stored in the per-process information, the
shell builtin ulimit command must directly execute this system call if it
is to affect all future processes created by the shell.

The value of the current limit of the following resources affect these
implementation defined parameters:

Limit Implementation Defined Constant
RLIMIT_FSIZE FCHR_MAX
RLIMIT_NOFILE OPEN_MAX

When using the getrlimit() function, if a resource limit can be
represented correctly in an object of type rlim_t, then its
representation is returned; otherwise, if the value of the resource limit
is equal to that of the corresponding saved hard limit, the value
returned is RLIM_SAVED_MAX; otherwise the value returned is
RLIM_SAVED_CUR.

When using the setrlimit() function, if the requested new limit is
RLIM_INFINITY, the new limit will be "no limit"; otherwise if the
requested new limit is RLIM_SAVED_MAX, the new limit will be the
corresponding saved hard limit; otherwise, if the requested new limit is
RLIM_SAVED_CUR, the new limit will be the corresponding saved soft limit;
otherwise, the new limit will be the requested value. In addition, if the
corresponding saved limit can be represented correctly in an object of
type rlim_t, then it will be overwritten with the new limit.

The result of setting a limit to RLIM_SAVED_MAX or RLIM_SAVED_CUR is
unspecified unless a previous call to getrlimit() returned that value as
the soft or hard limit for the corresponding resource limit.

A limit whose value is greater than RLIM_INFINITY is permitted.

The exec family of functions also cause resource limits to be saved. See
exec(2).

RETURN VALUES

Upon successful completion, getrlimit() and setrlimit() return 0.
Otherwise, these functions return -1 and set errno to indicate the error.

ERRORS

The getrlimit() and setrlimit() functions will fail if:

EFAULT
The rlp argument points to an illegal address.

EINVAL
An invalid resource was specified; or in a setrlimit() call,
the new rlim_cur exceeds the new rlim_max.

EPERM
The limit specified to setrlimit() would have raised the
maximum limit value and {PRIV_SYS_RESOURCE} is not asserted in
the effective set of the current process.

The setrlimit() function may fail if:

EINVAL
The limit specified cannot be lowered because current usage is
already higher than the limit.

USAGE

The getrlimit() and setrlimit() functions have transitional interfaces
for 64-bit file offsets. See lf64(7).

The rlimit functionality is now provided by the more general resource
control facility described on the setrctl(2) manual page. The actions
associated with the resource limits described above are true at system
boot, but an administrator can modify the local configuration to modify
signal delivery or type. Application authors that utilize rlimits for the
purposes of resource awareness should investigate the resource controls
facility.

ATTRIBUTES