getrlimit(2) manual page
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getrlimit, setrlimit - control maximum system resource consumption
#include <sys/time.h>
#include <sys/resource.h>
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 getrlimit() and set with 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 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. Limits may have an ‘infinite’
value of RLIM_INFINITY
. 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 */
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 in the table 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. This is a soft limit only.
- SIGXCPU
- 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.
- brk(2)
- 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.
- SIGXFSZ
- 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.
- SIGSEGV
- 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.
- 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.
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
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.
Under the following conditions, the functions getrlimit()
and setrlimit() fail and set errno to:
- EFAULT
- rlp 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 the effective
user of the calling process is not super-user.
brk(2)
, open(2)
, sigaltstack(2)
,
malloc(3C)
, signal(3C)
, signal(5)
- RLIMIT_STACK:
- 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. Therefore, to
guarantee that the process stack can grow to the limit, you must alter
the limit prior to the execution of the process in which the new stack
size is to be used.
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