"Linux Advanced Programming" (chapter eighth) process management and program development 4

Modify process user-related information

int access (__const char *__name, int __type): Detects whether the current process has access to a file

Parameter 1: Files to be accessed

Parameter 2: corresponding permission 4 (R_ok readable), 2 (W_ok writable), 1 (X_OK executable), 0 (F_OK file exists)

Returns 0 if it has permission, otherwise 1. Error status includes eacces (no access), ENOENT (file does not exist), erofs (read-only file system requires write permission)

int i; if ((i = Access ("/etc/exports", x_ok)) = =-1) {    perror ("  Access");    Exit (exit_failure);} Else {    //...}

int setuid (__uid_t __uid): Set process Real user Ruid

The real user number with the preset value.

Super User execution: will set the real user number UID, valid user number Euid to the specified ID, and return 0 for success.

Normal user execution: If set to its own UID value, can be successful; otherwise not authorized to modify, return-1.

#include <stdio.h>#include<unistd.h>#include<stdlib.h>intMain () {intuid, euid, suid; Getresuid (&uid, &euid, &suid); printf ("uid =%d, Euid =%d, suid =%d\n", UID, euid, suid); printf ("After setuid (501) \ n"); Setuid (501); UID= -1; Euid= -1; Suid= -1; Getresuid (&uid, &euid, &suid); printf ("uid =%d, Euid =%d, suid =%d\n", UID, euid, suid); return 0;}

Root user execution results, can be successfully modified

Normal user execution results, non-modifiable

int Setgid (__gid_t __gid): The GID of the process user has been modified, using the same method as setuid.

int Seteuid (__uid_t __uid): Set Valid user number Euid

Super User: Set valid user number to the specified ID, successfully returned 0, failed to return-1;

Normal User: Can be set to its own ID, set to another failure.

int Setegid (__gid_t __gid): Set valid user group ID

int Setreuid (__uid_t __ruid, __uid_t __euid): Set Ruid and Euid at the same time

int Setregid (__gid_t __rgid, __gid_t __egid): Set up both real user groups and active user groups

"Linux Advanced Programming" (chapter eighth) process management and program development 4