GETRLIMIT(P) POSIX Programmer's Manual GETRLIMIT(P)NAME
getrlimit, setrlimit - control maximum resource consumption
SYNOPSIS
#include <sys/resource.h>
int getrlimit(int resource, struct rlimit *rlp);
int setrlimit(int resource, const struct rlimit *rlp);
DESCRIPTION
The getrlimit() function shall get, and the setrlimit() function shall
set, limits on the consumption of a variety of resources.
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 represented by an rlimit structure. The rlim_cur member speci‐
fies the current or soft limit and the rlim_max member specifies the
maximum or 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 appropriate privileges
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.
The value RLIM_INFINITY, defined in <sys/resource.h>, shall be consid‐
ered to be larger than any other limit value. If a call to getrlimit()
returns RLIM_INFINITY for a resource, it means the implementation shall
not enforce limits on that resource. Specifying RLIM_INFINITY as any
resource limit value on a successful call to setrlimit() shall inhibit
enforcement of that resource limit.
The following resources are defined:
RLIMIT_CORE
This is the maximum size of a core file, in bytes, that may be
created by a process. A limit of 0 shall prevent the creation of
a core file. If this limit is exceeded, the writing of a core
file shall terminate at this size.
RLIMIT_CPU
This is the maximum amount of CPU time, in seconds, used by a
process. If this limit is exceeded, SIGXCPU shall be generated
for the process. If the process is catching or ignoring SIGXCPU,
or all threads belonging to that process are blocking SIGXCPU,
the behavior is unspecified.
RLIMIT_DATA
This is the maximum size of a process' data segment, in bytes.
If this limit is exceeded, the malloc() function shall fail with
errno set to [ENOMEM].
RLIMIT_FSIZE
This is the maximum size of a file, in bytes, that may be cre‐
ated by a process. If a write or truncate operation would cause
this limit to be exceeded, SIGXFSZ shall be generated for the
thread. If the thread is blocking, or the process is catching
or ignoring SIGXFSZ, continued attempts to increase the size of
a file from end-of-file to beyond the limit shall fail with
errno set to [EFBIG].
RLIMIT_NOFILE
This is a number one greater than the maximum value that the
system may assign to a newly-created descriptor. If this limit
is exceeded, functions that allocate a file descriptor shall
fail with errno set to [EMFILE]. This limit constrains the num‐
ber of file descriptors that a process may allocate.
RLIMIT_STACK
This is the maximum size of a process' stack, in bytes. The
implementation does not automatically grow the stack beyond this
limit. If this limit is exceeded, SIGSEGV shall be generated for
the thread. If the thread is blocking SIGSEGV, or the process is
ignoring or catching SIGSEGV and has not made arrangements to
use an alternate stack, the disposition of SIGSEGV shall be set
to SIG_DFL before it is generated.
RLIMIT_AS
This is the maximum size of a process' total available memory,
in bytes. If this limit is exceeded, the malloc() and mmap()
functions shall fail with errno set to [ENOMEM]. In addition,
the automatic stack growth fails with the effects outlined
above.
When using the getrlimit() function, if a resource limit can be repre‐
sented 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 shall be
RLIM_SAVED_MAX; otherwise, the value returned shall be RLIM_SAVED_CUR.
When using the setrlimit() function, if the requested new limit is
RLIM_INFINITY, the new limit shall be "no limit''; otherwise, if the
requested new limit is RLIM_SAVED_MAX, the new limit shall be the cor‐
responding saved hard limit; otherwise, if the requested new limit is
RLIM_SAVED_CUR, the new limit shall be the corresponding saved soft
limit; otherwise, the new limit shall be the requested value. In addi‐
tion, if the corresponding saved limit can be represented correctly in
an object of type rlim_t then it shall 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.
The determination of whether a limit can be correctly represented in an
object of type rlim_t is implementation-defined. For example, some
implementations permit a limit whose value is greater than RLIM_INFIN‐
ITY and others do not.
The exec family of functions shall cause resource limits to be saved.
RETURN VALUE
Upon successful completion, getrlimit() and setrlimit() shall return 0.
Otherwise, these functions shall return -1 and set errno to indicate
the error.
ERRORS
The getrlimit() and setrlimit() functions shall fail if:
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 the calling process does not have appropriate
privileges.
The setrlimit() function may fail if:
EINVAL The limit specified cannot be lowered because current usage is
already higher than the limit.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
If a process attempts to set the hard limit or soft limit for
RLIMIT_NOFILE to less than the value of {_POSIX_OPEN_MAX} from <lim‐
its.h>, unexpected behavior may occur.
If a process attempts to set the hard limit or soft limit for
RLIMIT_NOFILE to less than the highest currently open file descriptor
+1, unexpected behavior may occur.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSOexec() , fork() , malloc() , open() , sigaltstack() , sysconf() ,
ulimit() , the Base Definitions volume of IEEE Std 1003.1-2001,
<stropts.h>, <sys/resource.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online
at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 GETRLIMIT(P)
