5th. Process Environment (4) _ Process resource limit

5. Process Resource Limitations

(1) Getrlimit, Setrlimit function

Header file	#include <sys/resource.h>
Function	int* getrlimit (int resource, struct rlimit* rlptr);
return value	Successfully returned 0, error returned non 0
Function	Access to resource limits, stored in rlptr-pointed structures
Parameters	(1) Rlimit structural body struct rlimit{ rlim_t rlim_cur; // Soft limit: current limit rlim_t Rlim_max; // Hard limit: Maximum value of Rlim_cur } (2) The value of resource: see the following table.
Function	int setrlimit (int resource, const struct rlimit* rlptr);
return value	Successfully returned 0, error returned non 0
Function	Modify the resource limits specified by the resource by RLPTR the structure to which it is directed
Note	Resource constraints affect the calling process and are inherited by its child processes.

(2) Resource value

Macro	Role
Rlimit_as	Process Available Storage size
Rlimit_core	Maximum number of bytes in the core file
Rlimit_cpu	CPU Time Max
Rlimit_data	Maximum length of data segment
Rlimit_fsize	The maximum length of the file that can be created. When this soft limit is exceeded, a sigxfsz signal is sent to the process
Rlimit_locks	Maximum number of file locks
Rlimit_memlock	Maximum number of bytes that can be locked in memory using Mlock
Rlimit_nofile	Maximum number of files that can be opened
Rlimit_nproc	The maximum number of child processes that each user ID can have
Rlimit_rss	Byte length of the maximum resident memory set
Rlimit_stact	Maximum length of stack

"Programming Experiment" shows process resource limitations

Process_limit.c

#include <sys/resource.h>#include<stdio.h>#include<stdlib.h>#defineRlimit (name) get_limit (#name, name);voidGet_limit (Char* Name,intResource) {    structRlimit limit; if(Getrlimit (Resource, &limit) <0) {perror ("Getrlimit Error"); return; } printf ("%-15s", name);//left aligns the name of the print resource//rlmit_cur: Soft Resource limits    if(Limit.rlim_cur = =rlim_infinity) {printf ("Infinity");//Unlimited}Else{printf ("%10ld", Limit.rlim_cur); }    //Rlimit_max: Hard Resource limits    if(Limit.rlim_max = =rlim_infinity) {printf ("Infinity");//Unlimited}Else{printf ("%10ld", Limit.rlim_max); } printf ("\ n");}intMainintargcChar*argv[])       {Rlimit (rlimit_as); //process available Storage sizeRlimit (Rlimit_core);//maximum number of bytes in the core fileRlimit (RLIMIT_CPU);//CPU Time MaxRlimit (Rlimit_data);//Maximum length of data segmentRlimit (rlimit_fsize);//maximum length of file that can be createdRlimit (rlimit_locks);//maximum number of file locksRlimit (Rlimit_memlock);//maximum number of bytes that can be locked in memory using MlockRlimit (Rlimit_nofile);//maximum number of files that can be openedRlimit (RLIMIT_NPROC);//the maximum number of child processes that each user ID can haveRlimit (RLIMIT_RSS);//byte length of the maximum resident memory setRlimit (Rlimit_stack);//maximum length of stack        return 0;}

(3) configuration file for process resource limit

①/etc/security/limits.conf

Initialization of process resources in ②linux is established by process No. 0 and inherited by subsequent processes .

(4) modification rules for resource limitations

① Hard resource limit must be greater than or equal to soft resource limit

② any process can reduce or elevate its soft resource limit , but must be less than or equal to the hard resource limit .

③ any process can reduce its hard resource limit, but must be greater than its soft limit, ordinary households do not reversible this operation.

④ only super users can increase the hard limit .

"Programming Experiment" limits the maximum number of open files for a process

Limit_nofile.c

#include <unistd.h>#include<sys/resource.h>#include<stdio.h>#include<stdlib.h>#include<fcntl.h>#defineMODE S_irwxu | S_irwxg | S_irwxointOpen_file (Const Char*filename) {    intFD = open (filename, O_RDWR | O_creat |O_trunc, MODE); if(FD <0) {perror ("Open Error"); Exit (1); }    returnFD;}intMainintargcChar*argv[]) {    structRlimit limit; Limit.rlim_cur=4;//set soft resource limitsLimit.rlim_max =1024x768;//set hard resource limits//set the maximum number of open files for a process//(note:0==> standard input 1== standard output 2==> standard error has been opened)    if(Setrlimit (Rlimit_nofile, &limit) <0) {perror ("Setrlimit Error"); Exit (1); }    //Open File    intfd1, FD2; FD1= Open_file ("S1.txt");//Open normally    if(Fd1 <0) {exit (1); } fd2= Open_file ("S2.txt");//if the 4 files specified by the soft resource limit are exceeded, an error is given.     if(Fd2 <0) {exit (1);    } close (FD1);        Close (FD2); return 0;}

5th. Process Environment (4) _ Process resource limit