System Calls getrlimit(2)
NAME
getrlimit, setrlimit - control maximum system resource con-
sumption
SYNOPSIS
#include
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
{PRIVSYSRESOURCE} 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
RLIMINFINITY. The rlp argument is a pointer to struct
rlimit that includes the following members:
rlimt rlimcur; /* current (soft) limit */
rlimt rlimmax; /* hard limit */
The type rlimt is an arithmetic data type to which objects
of type int, sizet, and offt 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:
RLIMITCORE 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
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System Calls getrlimit(2)
terminate at this size.
RLIMITCPU 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 schedul-
ing class defined.
RLIMITDATA The maximum size of a process's heap in
bytes. The brk(2) function will fail with
errno set to ENOMEM.
RLIMITFSIZE 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.
RLIMITNOFILE 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.
RLIMITSTACK 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 exe-
cution 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 RLIMITSTACK impacts only the main
thread's stack, and should be made only
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System Calls getrlimit(2)
from the main thread, if at all.
The SIGSEGV signal is sent to the process.
If the process is holding or ignoring SIG-
SEGV, 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 SIGDFL before it
is sent.
RLIMITVMEM 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.
RLIMITAS 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
RLIMITFSIZE FCHRMAX
RLIMITNOFILE OPENMAX
When using the getrlimit() function, if a resource limit can
be represented correctly in an object of type rlimt, 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 RLIMSAVEDMAX; oth-
erwise the value returned is RLIMSAVEDCUR.
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System Calls getrlimit(2)
When using the setrlimit() function, if the requested new
limit is RLIMINFINITY, the new limit will be "no limit";
otherwise if the requested new limit is RLIMSAVEDMAX, the
new limit will be the corresponding saved hard limit; other-
wise, if the requested new limit is RLIMSAVEDCUR, 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 rlimt, then it will be overwritten
with the new limit.
The result of setting a limit to RLIMSAVEDMAX or
RLIMSAVEDCUR 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 RLIMINFINITY is permit-
ted.
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.
ERORS
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 rlimcur exceeds the new
rlimmax.
EPERM The limit specified to setrlimit() would have
raised the maximum limit value and
{PRIVSYSRESOURCE} is not asserted in the effec-
tive 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.
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System Calls getrlimit(2)
USAGE
The getrlimit() and setrlimit() functions have transitional
interfaces for 64-bit file offsets. See lf64(5).
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 administra-
tor 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.
ATRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
ATRIBUTE TYPE ATRIBUTE VALUE
Interface Stability Standard
SEE ALSO
rctladm(1M), brk(2), exec(2), fork(2), open(2), setrctl(2),
sigaltstack(2), ulimit(2), getdtablesize(3C), malloc(3C),
signal(3C), signal.h(3HEAD), sysconf(3C), attributes(5),
lf64(5), privileges(5), resourcecontrols(5), standards(5)
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