GETRLIMIT(2) BSD Programmer's Manual GETRLIMIT(2)NAME
getrlimit, setrlimit - control maximum system resource consumption
SYNOPSIS
#include <sys/types.h>
#include <time.h>
#include <sys/resource.h>
int
getrlimit(int resource, struct rlimit *rlp);
int
getprlimit(int idtype, int id, int resource, struct rlimit *rlp);
int
setrlimit(int resource, const struct rlimit *rlp);
int
setprlimit(int idtype, int id, int resource, struct rlimit *rlp);
DESCRIPTION
Limits on the consumption of system resources by the a process and each
process it creates may be obtained with the getrlimit() or getprlimit()
call, and set with the setrlimit() or setprlimit() call.
The idtype and id specify the target of the call. The only idtype cur-
rently supported is P_PID. When the idtype is P_PID the id is the process
id of the process for which the limits will be retrieved or set. If the
process id is zero then the current process is the target. The getrlimit
and setrlimit calls are the same as getprlimit and setprlimit with idtype
set to P_PID and id set to 0. The resource parameter is one of the fol-
lowing:
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_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 us-
er 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 pro-
cesses 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. The rlimit structure is
used to specify the hard and soft limits on a resource,
struct rlimit {
quad_t rlim_cur; /* current (soft) limit */
quad_t rlim_max; /* hard limit */
};
Default values for the soft and hard limits are configured by login
classes in /etc/login.conf (see login.conf(8)) at login or session cre-
ation time.
Only the super-user may raise the maximum limits. Other users may only
alter rlim_cur within the range from 0 to rlim_max or (irreversibly) low-
er rlim_max.
For a process to have permission to retrieve or set the limits for anoth-
er process, the real or effective user ID of the target process must
match that of the calling process or the user must have appropriate priv-
ileges (such as given by a set-user-ID program or the user is the super-
user).
An ``infinite'' value for a limit is defined as RLIM_INFINITY. This value
should not be arbitrarily used to set the soft limit to the hard limit;
instead, use getrlimit to obtain the value of the hard limit.
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. Most shells have a limit, ulimit
or unlimit built-in command.
The system refuses to extend the data or stack space when the limits
would be exceeded in the normal way: a brk or sbrk call will fail if the
data space limit is reached. When the stack limit is reached, the pro-
cess receives 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 that the process'
soft limit will cause the write to fail and a signal SIGXFSZ to be gener-
ated; 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.
RETURN VALUES
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 location errno.
EXAMPLES
To increase the soft limit on RLIMIT_NOFILE to the hard limit, use:
if (getrlimit(RLIMIT_NOFILE, &rlim) != 0)
err(1, "getrlimit(RLIMIT_NOFILE)");
rlim.rlim_cur = rlim.rlim_max;
if (setrlimit(RLIMIT_NOFILE, &rlim) != 0)
err(1, "setrlimit(RLIMIT_NOFILE)")
ERRORSGetrlimit() and setrlimit() will fail if:
[EFAULT] The address specified for rlp is invalid.
[EINVAL] One of the parameters was invalid.
[ESRCH] The requested id could not be found.
[EPERM] The limit specified to setrlimit() would have raised the
maximum limit value, and the caller is not the super-user.
SEE ALSObash(1), quota(2), sigaltstack(2), sigvec(2), setusercontext(3),
sysctl(3), login.conf(5)HISTORY
The getrlimit function call appeared in 4.2BSD.
4th Berkeley Distribution June 4, 1993 3
