getrlimit, setrlimit - control maximum system resource con-
int getrlimit(int resource, struct rlimit *rlp);
int setrlimit(int resource, const struct rlimit *rlp);
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
an effective user ID of 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. Lim-
its may have an "infinite" value of RLIM_INFINITY. The rlp
argument is a pointer to struct rlimit that includes the
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
The possible resources, their descriptions, and the actions
taken when the current limit is exceeded are summarized as
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.
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 hold-
ing or ignoring
SIGXCPU, the behavior is scheduling class defined.
The maximum size of a process's heap in bytes. The
brk(2) function will fail with errno set to ENOMEM.
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
One more than the maximum value that the system may
assign to a newly created descriptor. This limit con-
strains the number of file descriptors that a process
The maximum size of a process's stack in bytes. The
system will not automatically grow the stack beyond
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 pro-
cess is holding or ignoring SIGSEGV, or is catching
SIGSEGV and has not made arrangements to use an alter-
nate stack (see sigaltstack(2)), the disposition of
SIGSEGV will be set to SIG_DFL before it is sent.
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.
This is the maximum size of a process's total avail-
able 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 out-
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
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; oth-
erwise 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; other-
wise, 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 permit-
The exec family of functions also cause resource limits to
be saved. See exec(2).
Upon successful completion, getrlimit() and setrlimit()
return 0. Otherwise, these functions return -1 and set errno
to indicate the error.
The getrlimit() and setrlimit() functions will fail if:
The rlp argument points to an illegal address.
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 the effective user of the
calling process is not super-user.
The setrlimit() function may fail if:
The limit specified cannot be lowered because current
usage is already higher than the limit.
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.
brk(2), exec(2), fork(2), open(2), setrctl(2),
sigaltstack(2), ulimit(2), getdtablesize(3C), malloc(3C),
signal(3C), signal(3HEAD), sysconf(3C), lf64(5)
Man(1) output converted with