C++ 以编程方式从 Unix 中的用户名获取 UID 和 GID？
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Programmatically getting UID and GID from username in Unix?
提问by Evan
I'm trying to use setuid() and setgid() to set the respective id's of a program to drop privileges down from root, but to use them I need to know the uid and gid of the user I want to change to.
我正在尝试使用 setuid() 和 setgid() 来设置程序的相应 id 以从 root 中删除权限，但要使用它们，我需要知道我想更改为的用户的 uid 和 gid。
Is there a system call to do this? I don't want to hardcode it or parse from /etc/passwd .
是否有系统调用来执行此操作？我不想对其进行硬编码或从 /etc/passwd 解析。
Also I'd like to do this programmatically rather than using:
此外，我想以编程方式执行此操作，而不是使用：
id -u USERNAME
id -u 用户名
Any help would be greatly appreciated
任何帮助将不胜感激
回答by jpalecek
Have a look at the getpwnam()and getgrnam()functions.
查看getpwnam()和getgrnam()函数。
回答by Matthew Flaschen
#include <sys/types.h>
#include <pwd.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
int main()
{
char *username = ...
struct passwd *pwd = calloc(1, sizeof(struct passwd));
if(pwd == NULL)
{
fprintf(stderr, "Failed to allocate struct passwd for getpwnam_r.\n");
exit(1);
}
size_t buffer_len = sysconf(_SC_GETPW_R_SIZE_MAX) * sizeof(char);
char *buffer = malloc(buffer_len);
if(buffer == NULL)
{
fprintf(stderr, "Failed to allocate buffer for getpwnam_r.\n");
exit(2);
}
getpwnam_r(username, pwd, buffer, buffer_len, &pwd);
if(pwd == NULL)
{
fprintf(stderr, "getpwnam_r failed to find requested entry.\n");
exit(3);
}
printf("uid: %d\n", pwd->pw_uid);
printf("gid: %d\n", pwd->pw_gid);
free(pwd);
free(buffer);
return 0;
}
回答by Tim Gilbert
回答by Joe
Look at getpwnam and struct passwd.
查看 getpwnam 和 struct passwd。
回答by Archit Jain
You can use the following code snippets:
您可以使用以下代码片段：
#include <pwd.h>
#include <grp.h>
gid_t Sandbox::getGroupIdByName(const char *name)
{
struct group *grp = getgrnam(name); /* don't free, see getgrnam() for details */
if(grp == NULL) {
throw runtime_error(string("Failed to get groupId from groupname : ") + name);
}
return grp->gr_gid;
}
uid_t Sandbox::getUserIdByName(const char *name)
{
struct passwd *pwd = getpwnam(name); /* don't free, see getpwnam() for details */
if(pwd == NULL) {
throw runtime_error(string("Failed to get userId from username : ") + name);
}
return pwd->pw_uid;
}
Ref: getpwnam()getgrnam()
