该过程需要某些资源(如CPU和内存)来执行任务.现在我们将查看相关的命令和系统调用，以了解有关资源利用率和监视的信息.默认情况下，对资源上的每个进程都有一定的限制，如果需要，可以增强限制以适应应用程序要求.
以下是使用命令的基本系统或进程资源信息 :
$ top
top命令不断显示系统资源的使用情况.如果任何进程将系统置于某种挂起状态(消耗更多的CPU或内存)，则可以记录进程信息并采取适当的操作(例如终止相关进程).
$ ps
ps命令提供有关所有正在运行的进程的信息这有助于监视和控制进程.
$ vmstat
vmstat命令报告虚拟内存子系统的统计信息.它报告进程的信息(等待运行，休眠，可运行的进程等)，内存(虚拟内存信息，如空闲，使用等)，交换区域，IO设备，系统信息(中断数，上下文切换) )和CPU(用户，系统和空闲时间).
$ lsof
lsof命令打印所有当前正在运行的进程的打开文件列表，包括系统进程.
$ getconf -a
getconf命令显示系统配置变量信息.
现在，让我们来看看相关的系统调用.
系统调用getrusage()，它提供有关系统资源使用情况的信息.
与访问和设置资源限制相关的系统调用，即getrlimit( )，setrlimit()，prlimit().
#include< sys/time.h> #include< sys/resource.h> int getrusage(int who，struct rusage * usage);
系统调用getrusage()返回有关系统资源使用情况的信息.这可以包括关于self，children或调用线程的信息，使用标志RUSAGE_SELF，RUSAGE_CHILDREN，RUSAGE_THREAD作为"who"变量.在调用之后，它返回结构rusage中的信息.
此调用在成功时返回"0"，在失败时返回"-1".
<请看下面的示例程序.
#include<stdio.h>
#include<sys/time.h>
#include<sys/resource.h>
void main(void) {
struct rusage res_usage;
int retval;
retval = getrusage(RUSAGE_SELF, &res_usage);
if (retval == -1) {
perror("getrusage error");
return;
}
printf("Details of getrusage:\n");
printf("User CPU time (seconds) is %d\n", (int)res_usage.ru_utime.tv_sec);
printf("User CPU time (micro seconds) is %d\n", (int)res_usage.ru_utime.tv_usec);
printf("Maximum size of resident set (kb) is %ld\n", res_usage.ru_maxrss);
printf("Soft page faults (I/O not required) is %ld\n", res_usage.ru_minflt);
printf("Hard page faults (I/O not required) is %ld\n", res_usage.ru_majflt);
printf("Block input operations via file system is %ld\n", res_usage.ru_inblock);
printf("Block output operations via file system is %ld\n", res_usage.ru_oublock);
printf("Voluntary context switches are %ld\n", res_usage.ru_nvcsw);
printf("Involuntary context switches are %ld\n", res_usage.ru_nivcsw);
return;
}Details of getrusage: User CPU time (seconds) is 0 User CPU time (micro seconds) is 0 Maximum size of resident set (kb) is 364 Soft page faults (I/O not required) is 137 Hard page faults (I/O not required) is 0 Block input operations via file system is 0 Block output operations via file system is 0 Voluntary context switches are 0 Involuntary context switches are 1
现在让我们看一下与访问和设置资源限制相关的系统调用./p>
#include< sys/time.h> #include< sys/resource.h> int getrlimit(int resource，struct rlimit * rlim); int setrlimit(int resource，const struct rlimit * rlim); int prlimit(pid_t pid，int resource，const struct rlimit * new_limit，struct rlimit * old_limit);
通过输入RLIMIT_NOFILE，RLIMIT_NPROC， RLIMIT_STACK等
系统调用 setrlimit()设置rlimit结构中提到的资源限制，直到限制范围内.
系统调用 prlimit()用于varius目的，例如用于检索当前资源限制或用于将资源限制更新为新值.
结构rlimit包含两个值 :
软限制 : 当前限额
硬限制 : 可以延长的最大限额.
RLIMIT_NOFILE
RLIMIT_NPROC : 可为该流程的用户创建的最大进程数.
RLIMIT_STACK : 该进程的堆栈段的最大字节数.
所有这些调用在成功时返回"0"，在失败时返回"-1".
让我们考虑以下使用getrlimit()系统调用的示例.
#include<stdio.h>
#include<sys/time.h>
#include<sys/resource.h>
void main(void) {
struct rlimit res_limit;
int retval;
int resources[] = {RLIMIT_NOFILE, RLIMIT_NPROC, RLIMIT_STACK};
int max_res;
int counter = 0;
printf("Details of resource limits for NOFILE, NPROC, STACK are as follows: \n");
max_res = sizeof(resources)/sizeof(int);
while (counter < max_res) {
retval = getrlimit(resources[counter], &res_limit);
if (retval == -1) {
perror("getrlimit error");
return;
}
printf("Soft Limit is %ld\n", res_limit.rlim_cur);
printf("Hard Limit (ceiling) is %ld\n", res_limit.rlim_max);
counter++;
}
return;
}Details of resource limits for NOFILE, NPROC, STACK are as follows: Soft Limit is 516 Hard Limit (ceiling) is 516 Soft Limit is 256 Hard Limit (ceiling) is 256 Soft Limit is 33554432 Hard Limit (ceiling) is 33554432
让我们考虑使用getrlimit()系统调用的另一个例子，但现在使用prlimit()系统调用.
#include<stdio.h>
#include<unistd.h>
#include<sys/time.h>
#include<sys/resource.h>
void main(void) {
struct rlimit res_limit;
int retval;
int resources[] = {RLIMIT_NOFILE, RLIMIT_NPROC, RLIMIT_STACK};
int max_res;
int counter = 0;
printf("Details of resource limits for NOFILE, NPROC, STACK using prlimit are as follows: \n");
max_res = sizeof(resources)/sizeof(int);
while (counter < max_res) {
retval = prlimit(getpid(), resources[counter], NULL, &res_limit);
if (retval == -1) {
perror("prlimit error");
return;
}
printf("Soft Limit is %ld\n", res_limit.rlim_cur);
printf("Hard Limit (ceiling) is %ld\n", res_limit.rlim_max);
counter++;
}
return;
}Details of resource limits for NOFILE, NPROC, STACK using prlimit are as follows: Soft Limit is 516 Hard Limit (ceiling) is 516 Soft Limit is 256 Hard Limit (ceiling) is 256 Soft Limit is 33554432 Hard Limit (ceiling) is 33554432
