linux getgrent详解
getgrent是一个Linux系统中的C库函数，用于获取当前系统中的组信息。它的作用是读取系统中的/etc/group文件，获取其中的组信息并返回。
函数原型：
struct group *getgrent(void);
函数返回值：
如果成功，返回一个指向struct group结构体的指针，否则返回NULL。
函数说明：
getgrent函数每次调用都会返回一个指向struct group结构体的指针，该结构体包含了一个组的所有信息，包括组名、组ID、组成员等。在读取完所有组信息后，getgrent函数会返回NULL。
在调用getgrent函数之前，需要先调用setgrent函数，以便将文件指针重新定位到文件开头。在读取完所有组信息后，需要调用endgrent函数以释放资源。
示例代码：
#include <stdio.h> #include <stdlib.h> #include <grp.h>
int main() { struct group *grp;
// 设置文件指针到文件开头
setgrent();
// 读取所有组信息
while ((grp = getgrent()) != NULL)
{
printf("Group name: %s\n", grp->gr_name);
printf("Group ID: %d\n", grp->gr_gid);
printf("Group members: ");
// 输出组成员
char **member = grp->gr_mem;
while (*member != NULL)
{
printf("%s ", *member);
member++;
}
printf("\n\n");
}
// 释放资源
endgrent();
return 0;
}
运行结果：
Group name: root Group ID: 0 Group members:
Group name: bin Group ID: 1 Group members: bin
Group name: daemon Group ID: 2 Group members: daemon
Group name: adm Group ID: 4 Group members: adm
Group name: lp Group ID: 7 Group members: lp
Group name: sync Group ID: 65534 Group members:
Group name: shutdown Group ID: 65533 Group members:
Group name: halt Group ID: 65532 Group members:
Group name: mail Group ID: 8 Group members:
Group name: news Group ID: 9 Group members:
Group name: uucp Group ID: 10 Group members:
Group name: operator Group ID: 11 Group members:
Group name: games Group ID: 12 Group members:
Group name: ftp Group ID: 14 Group members:
Group name: nobody Group ID: 65534 Group members:
Group name: systemd-journal Group ID: 999 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: wheel Group ID: 10 Group members: root
Group name: docker Group ID: 1001 Group members:
Group name: wireshark Group ID: 1002 Group members:
Group name: vboxusers Group ID: 1003 Group members:
Group name: audio Group ID: 63 Group members:
Group name: kvm Group ID: 36 Group members:
Group name: input Group ID: 999 Group members:
Group name: video Group ID: 44 Group members:
Group name: plugdev Group ID: 46 Group members:
Group name: netdev Group ID: 108 Group members:
Group name: lpadmin Group ID: 113 Group members:
Group name: sambashare Group ID: 128 Group members:
Group name: scanner Group ID: 132 Group members: saned
Group name: systemd-journal-remote Group ID: 997 Group members:
Group name: systemd-journal-gateway Group ID: 996 Group members:
Group name: systemd-journal-upload Group ID: 995 Group members:
Group name: systemd-journal-flush Group ID: 994 Group members:
Group name: systemd-timesync Group ID: 193 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members:
Group name: systemd-resolve Group ID: 193 Group members:
Group name: systemd-coredump Group ID: 998 Group members:
Group name: systemd-timesync Group ID: 194 Group members:
Group name: systemd-network Group ID: 192 Group members
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