UNIX

• Programs
• Processes
• File Model
• Signal Model
• Process Control

Start-up Function and Environment List

• argc : 參數個數
• argv : 參數陣列，index 0 的參數為程式名稱本身
• envp : 環境變數
• extern : 可以聲明變數會在其他的位置(檔案)被定義

#include<stdio.h>
#include<stdlib.h>
 
int main(int argc,char *argv[], char *envp[])
{
    int i;
    for(i=0; envp[i] != (char *) 0 ;i++)
    {
        printf("%s\n",envp[i]);
    }
    exit(0);
}

#include<stdio.h>
#include<stdlib.h>
 
int main(int argc,char *argv[])
{
    extern char **environ;
    int i;
    for(i=0; environ[i] != (char *) 0 ;i++)
    {
        printf("%s\n",environ[i]);
    }
    exit(0);
}

提到 process 首先要了解一下程式執行時的記憶體分配狀況

這邊可以參考在修高等 UNIX 程式設計時的筆記 Process Environment:Memory Layout

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
 
int debug=1;       /* Initialized data segment */
char *progname;    /* Uninitialized data segment */
 
int main(int argc, char *argv[])
{
    int i;        /* Stack */
    char *ptr;    /* Stack */
 
    progname = argv[0];
    printf("argc = %d\n",argc);
 
    for(i = 1; i < argc; i++)
    {
        ptr = malloc(strlen(argv[i]) + 1);    /* Heap */
        strcpy(ptr, argv[i]);
 
        if(debug)
        {
            printf("%s\n",ptr);
        }
    }
}

每個 Process 也會有 Process ID，不同系統間可能有差異，但大致如下

• 0: a special kernel process for “scheduler”.
• 1: a special process,called “init”.
• 2: a kernel process, called “pagedaemon”.
• 3 ~ (2³²-1) : no special meaning.

User and Group

執行 process 時也會有使用者身份和群組的權限問題

這部分可參考 SUID & SGID in UNIX

#include <unistd.h>
#include <sys/types.h>
 
uid_t getuid(void);     /* returns the real user ID of the calling process. */
uid_t geteuid(void);    /* returns the effective user ID of the calling process. */
gid_t getgid(void);     /* returns the real group ID of the calling process. */
gid_t getegid(void);    /* returns the effective group ID of the calling process. */

#include <sys/types.h>
#include <pwd.h>
 
struct passwd *getpwnam(const char *name);
struct passwd *getpwuid(uid_t uid);
 
struct passwd {
    char   *pw_name;       /* username */
    char   *pw_passwd;     /* user password */
    uid_t   pw_uid;        /* user ID */
    gid_t   pw_gid;        /* group ID */
    char   *pw_gecos;      /* user information */
    char   *pw_dir;        /* home directory */
    char   *pw_shell;      /* shell program */
};