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getrlimit(2) [redhat man page]

GETRLIMIT(2)						     Linux Programmer's Manual						      GETRLIMIT(2)

getrlimit, getrusage, setrlimit - get/set resource limits and usage SYNOPSIS
#include <sys/time.h> #include <sys/resource.h> #include <unistd.h> int getrlimit(int resource, struct rlimit *rlim); int getrusage(int who, struct rusage *usage); int setrlimit(int resource, const struct rlimit *rlim); DESCRIPTION
getrlimit and setrlimit get and set resource limits respectively. Each resource has an associated soft and hard limit, as defined by the rlimit structure (the rlim argument to both getrlimit() and setrlimit()): struct rlimit { rlim_t rlim_cur; /* Soft limit */ rlim_t rlim_max; /* Hard limit (ceiling for rlim_cur) */ }; The soft limit is the value that the kernel enforces for the corresponding resource. The hard limit acts as a ceiling for the soft limit: an unprivileged process may only set its soft limit to a value in the range from 0 up to the hard limit, and (irreversibly) lower its hard limit. A privileged process may make arbitrary changes to either limit value. The value RLIM_INFINITY denotes no limit on a resource (both in the structure returned by getrlimit() and in the structure passed to setr- limit()). resource must be one of: RLIMIT_CPU CPU time limit in seconds. When the process reaches the soft limit, it is sent a SIGXCPU signal. The default action for this sig- nal is to terminate the process. However, the signal can be caught, and the handler can return control to the main program. If the process continues to consume CPU time, it will be sent SIGXCPU once per second until the hard limit is reached, at which time it is sent SIGKILL. (This latter point describes Linux 2.2 and 2.4 behaviour. Implementations vary in how they treat processes which continue to consume CPU time after reaching the soft limit. Portable applications that need to catch this signal should perform an orderly termination upon first receipt of SIGXCPU.) RLIMIT_DATA The maximum size of the process's data segment (initialized data, uninitialized data, and heap). This limit affects calls to brk() and sbrk(), which fail with the error ENOMEM upon encountering the soft limit of this resource. RLIMIT_FSIZE The maximum size of files that the process may create. Attempts to extend a file beyond this limit result in delivery of a SIGXFSZ signal. By default, this signal terminates a process, but a process can catch this signal instead, in which case the relevant sys- tem call (e.g., write(), truncate()) fails with the error EFBIG. RLIMIT_LOCKS A limit on the combined number of flock() locks and fcntl() leases that this process may establish (Linux 2.4 and later). RLIMIT_MEMLOCK The maximum number of bytes of virtual memory that may be locked into RAM using mlock() and mlockall(). RLIMIT_NOFILE Specifies a value one greater than the maximum file descriptor number that can be opened by this process. Attempts (open(), pipe(), dup(), etc.) to exceed this limit yield the error EMFILE. RLIMIT_NPROC The maximum number of processes that can be created for the real user ID of the calling process. Upon encountering this limit, fork() fails with the error EAGAIN. RLIMIT_RSS Specifies the limit (in pages) of the process's resident set (the number of virtual pages resident in RAM). This limit only has effect in Linux 2.4 onwatrds, and there only affects calls to madvise() specifying MADVISE_WILLNEED. RLIMIT_STACK The maximum size of the process stack, in bytes. Upon reaching this limit, a SIGSEGV signal is generated. To handle this signal, a process must employ an alternate signal stack (sigaltstack(2)). RLIMIT_OFILE is the BSD name for RLIMIT_NOFILE. getrusage returns the current resource usages, for a who of either RUSAGE_SELF or RUSAGE_CHILDREN. The former asks for resources used by the current process, the latter for resources used by those of its children that have terminated and have been waited for. struct rusage { struct timeval ru_utime; /* user time used */ struct timeval ru_stime; /* system time used */ long ru_maxrss; /* maximum resident set size */ long ru_ixrss; /* integral shared memory size */ long ru_idrss; /* integral unshared data size */ long ru_isrss; /* integral unshared stack size */ long ru_minflt; /* page reclaims */ long ru_majflt; /* page faults */ long ru_nswap; /* swaps */ long ru_inblock; /* block input operations */ long ru_oublock; /* block output operations */ long ru_msgsnd; /* messages sent */ long ru_msgrcv; /* messages received */ long ru_nsignals; /* signals received */ long ru_nvcsw; /* voluntary context switches */ long ru_nivcsw; /* involuntary context switches */ }; RETURN VALUE
On success, zero is returned. On error, -1 is returned, and errno is set appropriately. ERRORS
EFAULT rlim or usage points outside the accessible address space. EINVAL getrlimit or setrlimit is called with a bad resource, or getrusage is called with a bad who. EPERM A non-superuser tries to use setrlimit() to increase the soft or hard limit above the current hard limit, or a superuser tries to increase RLIMIT_NOFILE above the current kernel maximum. CONFORMING TO
SVr4, BSD 4.3 NOTE
Including <sys/time.h> is not required these days, but increases portability. (Indeed, struct timeval is defined in <sys/time.h>.) On Linux, if the disposition of SIGCHLD is set to SIG_IGN then the resource usages of child processes are automatically included in the value returned by RUSAGE_CHILDREN, although POSIX 1003.1-2001 explicitly prohibits this. The above struct was taken from BSD 4.3 Reno. Not all fields are meaningful under Linux. Right now (Linux 2.4) only the fields ru_utime, ru_stime, ru_minflt, ru_majflt, and ru_nswap are maintained. SEE ALSO
dup(2), fcntl(2), fork(2), mlock(2), mlockall(2), mmap(2), open(2), quotactl(2), sbrk(2), wait3(2), wait4(2), malloc(3), ulimit(3), sig- nal(7) Linux 2002-07-09 GETRLIMIT(2)

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