uname()系统调用学习

uname()系统调用返回了一系列关于主机系统的标识信息。

#include <sys/utsname.h>

int uname(struct utsname *utsbuf);

　　　　　　　　　　　　Returns 0 on success, or -1 on error

#define _UTSNAME_LENGTH 65

struct utsname{

　　char sysname[_UTSNAME_LENGTH];    /*Implementation name*/

　　char nodename[_UTSNAME_LENGTH];  /*Node name on network*/

　　char release[_UTSNAME_LENGTH];      /*Implementation release level*/

　　char version[_UTSNAME_LENGTH];      /*Release version level*/

　　char machine[_UTSNAME_LENGTH];     /*Hardware on which system is running*/

　　char domainname[_UTSNAME_LENGTH]; /*NIS domain name of host*/

};

#include <stdio.h>
#include <sys/utsname.h>

int main() {
    struct utsname uts;
    if(uname(&uts) == -1) {
        fprintf(stderr, "uname.\n");
        return -1;
    }

    printf("Node name: %s\n", uts.nodename);
    printf("system name: %s\n", uts.sysname);
    printf("release: %s\n", uts.release);
    printf("version: %s\n", uts.release);
    printf("machine: %s\n", uts.machine);
    printf("domainname: %s\n", uts.__domainname);

    return 0;
}

输出：

Node name: hahaha
system name: Linux
release: 4.18.0-240.22.1.el8_3.x86_64
version: 4.18.0-240.22.1.el8_3.x86_64
machine: x86_64
domainname: (none)

查看了本机utsname.h头文件，发现里面有如下几行

_GNU_SOURCE is the only one you should ever define yourself. 

__USE_GNU is defined internally through a mechanism in features.h (which is included by all other glibc headers)

when _GNU_SOURCE is defined, and possibly under other conditions.

Defining or undefining __USE_GNU yourself will badly break the glibc headers.