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Manuál Linux
[Linux manuál]

getrlimit, getrusage, setrlimit: získej / nastav limity prostředků a využití

Originální popis anglicky: getrlimit, getrusage, setrlimit - get/set resource limits and usage

Návod, kniha: Linux Programmer's Manual


#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);


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 (under Linux: one with the CAP_SYS_RESOURCE capability) 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 setrlimit()).
resource must be one of:
The maximum size of the process's virtual memory (address space) in bytes. This limit affects calls to brk(2), mmap(2) and mremap(2), which fail with the error ENOMEM upon exceeding this limit. Also automatic stack expansion will fail (and generate a SIGSEGV that kills the process when no alternate stack has been made available). Since the value is a long, on machines with a 32-bit long either this limit is at most 2 GiB, or this resource is unlimited.
Maximum size of core file. When 0 no core dump files are created. When nonzero, larger dumps are truncated to this size.
CPU time limit in seconds. When the process reaches the soft limit, it is sent a SIGXCPU signal. The default action for this signal 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.)
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.
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 system call (e.g., write(), truncate()) fails with the error EFBIG.
A limit on the combined number of flock() locks and fcntl() leases that this process may establish. (Early Linux 2.4 only.)
The maximum number of bytes of virtual memory that may be locked into RAM using mlock() and mlockall().
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.
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.
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.
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)).
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 */


On success, zero is returned. On error, -1 is returned, and errno is set appropriately.


rlim or usage points outside the accessible address space.
getrlimit or setrlimit is called with a bad resource, or getrusage is called with a bad who.
An unprivileged process tried to use setrlimit() to increase a soft or hard limit above the current hard limit; the CAP_SYS_RESOURCE capability is required to do this. Or, the process tried to use setrlimit() to increase the soft or hard RLIMIT_NOFILE limit above the current kernel maximum (NR_OPEN).


SVr4, BSD 4.3


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, 2.6) only the fields ru_utime, ru_stime, ru_minflt, ru_majflt, and ru_nswap are maintained.


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), capabilities(7), signal(7)
2004-06-16 Linux
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