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1. 口令文件

/etc/passwd

root:x:0:0:root:/root:/bin/bash
squid:x:23:23::/var/spool/squid:/dev/null
nobody:x:65534:65534:Nobody:/home:/bin/sh
sar:x:205:105:Stephen Rago:/home/sar:/bin/bash

通过命令查看用户信息：

$ finger -p sar
Login: sar Name: Steve Rago
Directory: /home/sar Shell: /bin/sh
Office: SF 5-121, 555-1111 Home Phone: 555-2222
On since Mon Jan 19 03:57 (EST) on ttyv0 (messages off)
No Mail.

通过函数查看用户信息：

#include <pwd.h>
struct passwd *getpwuid(uid_t uid);
struct passwd *getpwnam(const char *name);

如果要查看整个文件的记录项：

#include <pwd.h>
struct passwd *getpwent(void);
//Returns: pointer if OK, NULL on error or end of file

void setpwent(void);
void endpwent(void);

2. 阴影口令

#include <shadow.h>
struct spwd *getspnam(const char *name);
struct spwd *getspent(void);
// Both return: pointer if OK, NULL on error
void setspent(void);
void endspent(void);

3. 组文件

#include <grp.h>
struct group *getgrgid(gid_t gid);
struct group *getgrnam(const char *name);

#include <grp.h>
struct group *getgrent(void);
// Returns: pointer if OK, NULL on error or end of file
void setgrent(void);
void endgrent(void);

4. 附属组ID

#include <unistd.h>
int getgroups(int gidsetsize, gid_t grouplist[]);
// Returns: number of supplementary group IDs if OK, −1 on error
#include <grp.h> /* on Linux */
#include <unistd.h> /* on FreeBSD, Mac OS X, and Solaris */
int setgroups(int ngroups, const gid_t grouplist[]);
#include <grp.h> /* on Linux and Solaris */
#include <unistd.h> /* on FreeBSD and Mac OS X */
int initgroups(const char *username, gid_t basegid);
// Both return: 0 if OK, −1 on error

5. 实现区别

Ref : 148

6. 其他数据文件

一般情况，对每个数据文件至少有3个函数：

  • get()
  • set()
  • end()

6-6

7. 登录账户记录

struct utmp {
    char ut_line[8]; /* tty line: "ttyh0", "ttyd0", "ttyp0", ... */
    char ut_name[8]; /* login name */
    long ut_time; /* seconds since Epoch */
};

8. 系统标识

#include <sys/utsname.h>
int uname(struct utsname *name);
// Returns: non-negative value if OK, −1 on error

struct utsname {
    char sysname[]; /* name of the operating system */
    char nodename[]; /* name of this node */
    char release[]; /* current release of operating system */
    char version[]; /* current version of this release */
    char machine[]; /* name of hardware type */
};

历史上，有只返回主机名的接口：

#include <unistd.h>
int gethostname(char *name, int namelen);
// Returns: 0 if OK, −1 on error

9. 时间和日期

ref : https://github.com/breakerthb/LinuxPrograming/blob/master/NoteBook/Time.md