GETRLIMIT(2) BSD Programmer's Manual GETRLIMIT(2)
getrlimit, setrlimit - control maximum system resource consumption
#include <sys/resource.h>
int
getrlimit(int resource, struct rlimit *rlp);
int
setrlimit(int resource, const struct rlimit *rlp);
Limits on the consumption of system resources by the current process and
each process it creates may be obtained with the getrlimit() call, and
set with the setrlimit() call.
The resource parameter is one of the following:
RLIMIT_CORE The largest size (in bytes) core file that may be creat-
ed.
RLIMIT_CPU The maximum amount of CPU time (in seconds) to be used by
each process.
RLIMIT_TIME The maximum amount of human time (in seconds) to be used
by each process.
RLIMIT_DATA The maximum size (in bytes) of the data segment for a
process; this defines how far a program may extend its
break with the sbrk(2) system call.
RLIMIT_FSIZE The largest size (in bytes) file that may be created.
RLIMIT_MEMLOCK The maximum size (in bytes) which a process may lock into
memory using the mlock(2) function.
RLIMIT_NOFILE The maximum number of open files for this process.
RLIMIT_NPROC The maximum number of simultaneous processes for this
user id.
RLIMIT_RSS The maximum size (in bytes) to which a process's resident
set size may grow. This imposes a limit on the amount of
physical memory to be given to a process; if memory is
tight, the system will prefer to take memory from
processes that are exceeding their declared resident set
size.
RLIMIT_STACK The maximum size (in bytes) of the stack segment for a
process; this defines how far a program's stack segment
may be extended. Stack extension is performed automati-
cally by the system.
A resource limit is specified as a soft limit and a hard limit. When a
soft limit is exceeded a process may receive a signal (for example, if
the CPU time or file size is exceeded), but it will be allowed to contin-
ue execution until it reaches the hard limit (or modifies its resource
limit). The rlimit structure is used to specify the hard and soft limits
on a resource,
struct rlimit {
rlim_t rlim_cur; /* current (soft) limit */
rlim_t rlim_max; /* hard limit */
};
Only the superuser may raise the maximum limits. Other users may only
alter rlim_cur within the range from 0 to rlim_max or (irreversibly)
lower rlim_max.
An "infinite" value for a limit is defined as RLIM_INFINITY.
A value of RLIM_SAVED_CUR or RLIM_SAVED_MAX will be stored in rlim_cur or
rlim_max respectively by getrlimit() if the value for the current or max-
imum resource limit cannot be stored in an rlim_t. The values
RLIM_SAVED_CUR and RLIM_SAVED_MAX should not be used in a call to
setrlimit() unless they were returned by a previous call to getrlimit().
Because this information is stored in the per-process information, this
system call must be executed directly by the shell if it is to affect all
future processes created by the shell; limit is thus a built-in command
to csh(1) and ulimit is the sh(1) equivalent.
The system refuses to extend the data or stack space when the limits
would be exceeded in the normal way: a brk(2) call fails if the data
space limit is reached. When the stack limit is reached, the process re-
ceives a segmentation fault (SIGSEGV); if this signal is not caught by a
handler using the signal stack, this signal will kill the process.
A file I/O operation that would create a file larger than the process'
soft limit will cause the write to fail and a signal SIGXFSZ to be gen-
erated; this normally terminates the process, but may be caught. When the
soft CPU time limit is exceeded, a signal SIGXCPU is sent to the offend-
ing process.
A 0 return value indicates that the call succeeded, changing or returning
the resource limit. A return value of -1 indicates that an error oc-
curred, and an error code is stored in the global variable errno.
getrlimit() and setrlimit() will fail if:
[EFAULT] The address specified for rlp is invalid.
[EPERM] The limit specified to setrlimit() would have raised the
maximum limit value, and the caller is not the superuser.
csh(1), sh(1), quotactl(2), sigaction(2), sigaltstack(2), sysctl(3)
The getrlimit() and setrlimit() function calls are expected to conform to
IEEE Std 1003.1-2004 ("POSIX.1").
The getrlimit() function call appeared in 4.2BSD.
MirBSD #10-current November 29, 2021 1