[系统运维] Linux Process

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[系统运维]Linux Process_control

文章目录

进程标识pid

id=0的是调度进程(swapper),该进程是内核的一部分,并不执行磁盘的任何的程序,也被称为系统进程
id=1 是init进程,属于用户态进程,但是以超级用户特权运行,是所有孤儿进程的父进程

#include <unistd.h>
pid_t getpid(void);
Returns: process ID of calling process
pid_t getppid(void);
Returns: parent process ID of calling process
uid_t getuid(void);
Returns: real user ID of calling process
uid_t geteuid(void);
Returns: effective user ID of calling process
gid_t getgid(void);
Returns: real group ID of calling process
gid_t getegid(void);
Returns: effective group ID of calling process

#include <unistd.h>
int setuid(uid_t uid);
int setgid(gid_t gid);
Both return: 0 if OK, ?1 on error

#include <unistd.h>
int setreuid(uid_t ruid, uid_t euid);
int setregid(gid_t rgid, gid_t egid);
Both return: 0 if OK, ?1 on error

fork

#include <unistd.h>
pid_t fork(void);
Returns: 0 in child, process ID of child in parent, ?1 on error

fork函数调用一次,返回两次,其中返回0是child进程,pid>0则是子进程的pid.内核一般保存父进程的区域堆栈,数据段的完全副本,且副本的访问权限只读,父进程或者子进程试图修改的话,内核就会建立修改区域的副本,(Copyy-On-Write)

在这里插入图片描述

wait and waitpid

#include <sys/wait.h>
pid_t wait(int *statloc);
pid_t waitpid(pid_t pid, int *statloc, int options);
/* Wait for a child to die. When one does, put its status in *STAT_LOC
and return its process ID. For errors, return (pid_t) -1.

This function is a cancellation point and therefore not marked with
__THROW. */
extern __pid_t wait (int *__stat_loc);


void tl::testProcess(){

	auto preStatus = [](int status)->void {
		if (WIFEXITED(status))
			printf("normal termination, exit status = %d\n",
				WEXITSTATUS(status));
		else if (WIFSIGNALED(status))
			printf("abnormal termination, signal number = %d%s\n",
				WTERMSIG(status),
#ifdef WCOREDUMP
				WCOREDUMP(status) ? " (core file generated)" : "");
#else
			"");
#endif
		else if (WIFSTOPPED(status))
			printf("child stopped, signal number = %d\n",
				WSTOPSIG(status));

	};

	pid_t pid;
	int status;
	if ((pid = fork()) < 0) {
		err_sys("fork error");
	}
	else if (pid == 0) /* child */
		exit(7);

	if (wait(&status) != pid) /* wait for child */
		err_sys("wait error");
	preStatus(status); /* and print its status */
	if ((pid = fork()) < 0) {
		err_sys("fork error");
	}
	else if (pid == 0) /* child */
		abort(); /* generates SIGABRT */
	if (wait(&status) != pid) /* wait for child */
		err_sys("wait error");

	preStatus(status); /* and print its status */
	if ((pid = fork()) < 0) {
		err_sys("fork error");
	}
	else if (pid == 0) /* child */
		status /= 0; /* divide by 0 generates SIGFPE */
	if (wait(&status) != pid) /* wait for child */
		err_sys("wait error");
	preStatus(status); /* and print its status */
	exit(0);
	

}


result:
└─$ ./tl.out
normal termination, exit status = 7
abnormal termination, signal number = 6
abnormal termination, signal number = 8

exec

该函数会创建一个进程，该进程完全取代原来的进程，从新进程的main开始执行

#include <unistd.h>
int execl(const char *pathname, const char arg0, … / (char *)0 */ );
int execv(const char *pathname, char *const argv[]);
int execle(const char *pathname, const char arg0, …
/ (char *)0, char *const envp[] */ );
int execve(const char *pathname, char *const argv[], char *const envp[]);
int execlp(const char *filename, const char arg0, … / (char *)0 */ );
int execvp(const char *filename, char *const argv[]);
int fexecve(int fd, char *const argv[], char *const envp[]);
All seven return: ?1 on error, no return on success

在这里插入图片描述

#include "log/logx.h"
#include <error.h>
#include<sys/wait.h>
#include <sys/resource.h>
#include <string.h>
void test();

int main() {
	test();
}

void test() {
	if (execl("/usr/bin/cal", "cal",nullptr) < 0) {
		LOGXF("error", strerror(errno));
	}
	else LOGXA("start succeed");//this will not run ,because execl will use this process 
}
/*
┌──(kali?kali)-[~/…/TestLinux/bin/x64/Debug]
└─$ sudo ./TestLinux.out
     April 2022
Su Mo Tu We Th Fr Sa
                1  2
 3  4  5  6  7  8  9
10 11 12 13 14 15 16
17 18 19 20 21 22 23
24 25 26 27 28 29 30

*/

用户标识

char *getlogin(void);
char *getuid(void);

#include "log/logx.h"
#include <error.h>
#include<sys/wait.h>

void test();

int main() {
	test();
}

void test() {
	LOGXA(VAR_DATA(getlogin()));
	LOGXA(VAR_DATA(getuid()));
}

进程调度

int nice(int incr);
Returns: new nice value ? NZERO if OK, ?1 on error
只会影响自己的值,不会影响其他进程的,incr越小优先级越大,系统会自动调整到合适的值

#include <sys/resource.h>
int getpriority(int which, id_t who);
Returns: nice value between ?NZERO and NZERO?1 if OK, ?1 on error

#include <sys/resource.h>
int setpriority(int which, id_t who, int value);
Returns: 0 if OK, ?1 on error

#include "log/logx.h"
#include <error.h>
#include<sys/wait.h>
#include <sys/resource.h>

void test();

int main() {
	test();
}

void test() {
	int result = nice(20);
	LOGXA(VAR_DATA(result));
	result = getpriority(PRIO_PROCESS, 0);
	LOGXA(VAR_DATA(result));
	result= setpriority(PRIO_PROCESS, 0, 25);
	LOGXA(VAR_DATA(result));
	result = getpriority(PRIO_PROCESS, 0);
	LOGXA(VAR_DATA(result));
}

┌──(kali?kali)-[~/…/TestLinux/bin/x64/Debug]
└─$ ./TestLinux.out
[+] log construction, can use it  /home/kali/projects/TestLinux/bin/x64/Debug/_log/log.html
[0]09:01:18[info][140028126343552]      [test]  result:  19   (test_main.cpp:14)
[1]09:01:18[info][140028126343552]      [test]  result:  19   (test_main.cpp:16)
[2]09:01:18[info][140028126343552]      [test]  result:  0   (test_main.cpp:18)
[3]09:01:18[info][140028126343552]      [test]  result:  19   (test_main.cpp:20)
[+] ~log deconstruction

进程关系

进程组

pid_t getpgrp(void); //获取进程组的gid

#include "log/logx.h"
#include <error.h>
#include<sys/wait.h>
#include <sys/resource.h>
void test();

int main() {
	test();
}

void test() {
	while (true){
		LOGXD(getpgrp());
		std::this_thread::sleep_for(std::chrono::seconds(1));
	}
}
/*
┌──(kali?kali)-[~]
└─$ /home/kali/projects/TestLinux/bin/x64/Debug/TestLinux.out
[+] log construction, can use it  /home/kali/_log/log.html
[0]06:13:12[debg][140493772470080]      [test]  138810   (test_main.cpp:16)
[1]06:13:13[debg][140493772470080]      [test]  138810   (test_main.cpp:16)
[2]06:13:14[debg][140493772470080]      [test]  138810   (test_main.cpp:16)
[3]06:13:15[debg][140493772470080]      [test]  138810   (test_main.cpp:16)
[4]06:13:16[debg][140493772470080]      [test]  138810   (test_main.cpp:16)
[5]06:13:17[debg][140493772470080]      [test]  138810   (test_main.cpp:16)
[6]06:13:18[debg][140493772470080]      [test]  138810   (test_main.cpp:16)
[7]06:13:19[debg][140493772470080]      [test]  138810   (test_main.cpp:16)
[8]06:13:20[debg][140493772470080]      [test]  138810   (test_main.cpp:16)
[9]06:13:21[debg][140493772470080]      [test]  138810   (test_main.cpp:16)
[10]06:13:22[debg][140493772470080]     [test]  138810   (test_main.cpp:16)




root      138715  0.0  0.0      0     0 ?        I    06:10   0:00 [kworker/u64:2-events_unbound]
kali      138810  0.0  0.0   6028  1824 pts/3    S+   06:13   0:00 /home/kali/projects/TestLinux/bin/x64/Debug/TestLinux.out
kali      138812  0.0  0.1   9800  3628 pts/0    R+   06:13   0:00 ps -aux
*/

pid_t getpgid(pid_t pid);
getpgid(0) == getpgrp()
int setpgid(pid_t pid, pid_t pgid);

#include "log/logx.h"
#include <error.h>
#include<sys/wait.h>
#include <sys/resource.h>
void test();

int main() {
	test();
}

void test() {
	while (true){
		LOGXD(VAR_DATA(getpgid(0)),VAR_DATA(getpgrp()),VAR_DATA(getpgid(139656)));
		std::this_thread::sleep_for(std::chrono::seconds(1));
	}
}
/*
└─$ /home/kali/projects/TestLinux/bin/x64/Debug/TestLinux.out                                                                                    130 ?
[+] log construction, can use it  /home/kali/_log/log.html
[0]06:48:56[debg][140477147711296]      [test]  getpgid(0):  139942  getpgrp():  139942  getpgid(139656):  139641   (test_main.cpp:13)
[1]06:48:57[debg][140477147711296]      [test]  getpgid(0):  139942  getpgrp():  139942  getpgid(139656):  139641   (test_main.cpp:13)
[2]06:48:58[debg][140477147711296]      [test]  getpgid(0):  139942  getpgrp():  139942  getpgid(139656):  139641   (test_main.cpp:13)
[3]06:48:59[debg][140477147711296]      [test]  getpgid(0):  139942  getpgrp():  139942  getpgid(139656):  139641   (test_main.cpp:13)
[4]06:49:00[debg][140477147711296]      [test]  getpgid(0):  139942  getpgrp():  139942  getpgid(139656):  139641   (test_main.cpp:13)

*/

session

一个session由一个或多个进程组组成

pid_t setsid(void); 该进程如果不是进程组的组长，则会新建会话，如果该进程是组长了则返回错误，解决的办法是fork进程，然后子进程会有单独的pid

void test() {
	if (setsid() == -1) {
		auto pid=fork();
		if (pid == 0) {
			LOGXD("child", getpid());
			LOGXD(VAR_DATA(setsid()));
			LOGXD(VAR_DATA(getsid(getpgid(0))));
		}
		else {
			LOGXD("parent", getpid());
		}
	}
}


/*


└─$ ./TestLinux.out
[+] log construction, can use it  /home/kali/projects/TestLinux/bin/x64/Debug/_log/log.html
[+] log construction, can use it  /home/kali/projects/TestLinux/bin/x64/Debug/_log/log.html
[0]07:12:43[debg][140152152371584]      [test]  child  140575   (test_main.cpp:15)
[0]07:12:43[debg][140152152371584]      [test]  parent  140574   (test_main.cpp:21)
[1]07:12:43[debg][140152152371584]      [test]  setsid():  140575   (test_main.cpp:16)
[2]07:12:43[debg][140152152371584]      [test]  getsid(getpgid(0)):  140575   (test_main.cpp:17)
[+] ~log deconstruction
[+] ~log deconstruction

*/

controlling Terminal

会话会存在一个控制终端，让会话和控制终端联系的叫控制进程，每个控制终端将会话分成一个前台进程组和若干后台进程组

需要有一种方法来通知内核哪一个进程组是前台进程组，这样，终端设备驱动程序就能了解将终端输入和终端产生的信号送到何处。

#include <unistd.h>
pid_t tcgetpgrp(int filedes); //返回值：若成功则返回前台进程组的进程组ID，出错则返回-1.
int tcsetpgrp(int filedes, pid_t pgrpid); //返回值：成功则返回0，出错则返回-1.

void test() {
	LOGXD("now_process_group_id:", VAR_DATA(getpgrp()));
	LOGXD("pre_process_group_id:" VAR_DATA(tcgetpgrp(STDIN_FILENO)));
	if (tcsetpgrp(STDIN_FILENO, getpgrp()) == 0) {
		LOGXD("pre_process_group_id:" VAR_DATA(tcgetpgrp(STDIN_FILENO)));
	}
	else {
		LOGXW("set fail");
	}
}
/*

└─$ ./TestLinux.out
[+] log construction, can use it  /home/kali/projects/TestLinux/bin/x64/Debug/_log/log.html
[0]07:41:27[debg][139648735146368]      [test]  now_process_group_id:  getpgrp():  141108   (test_main.cpp:12)
[1]07:41:27[debg][139648735146368]      [test]  pre_process_group_id:tcgetpgrp(0):  141108   (test_main.cpp:13)
[2]07:41:27[debg][139648735146368]      [test]  pre_process_group_id:tcgetpgrp(0):  141108   (test_main.cpp:15)
[+] ~log deconstruction

*/

job control

后台运行： xx &—（在后面加上&）
查看后台程序：jobs
将后台转入前台：fg %[后台序号]

/*
┌──(kali?kali)-[~/…/TestLinux/bin/x64/Debug]
└─$ ./TestLinux.out &
[1] 141243

[+] log construction, can use it  /home/kali/projects/TestLinux/bin/x64/Debug/_log/log.html
[0]07:52:55[debg][140687585276288]      [test]  now_process_group_id:  getpgrp():  141243   (test_main.cpp:12)
[1]07:52:55[debg][140687585276288]      [test]  pre_process_group_id:tcgetpgrp(0):  137600   (test_main.cpp:13)
[1]  + suspended (tty output)  ./TestLinux.out
┌──(kali?kali)-[~/…/TestLinux/bin/x64/Debug]
└─$ jobs                                                                                                                                           1 ?
[1]  + suspended (tty output)  ./TestLinux.out

┌──(kali?kali)-[~/…/TestLinux/bin/x64/Debug]
└─$ fg %1                                                                                                                                          1 ?
[1]  + continued  ./TestLinux.out
[2]07:53:04[debg][140687585276288]      [test]  pre_process_group_id:tcgetpgrp(0):  141243   (test_main.cpp:15)
[+] ~log deconstruction

┌──(kali?kali)-[~/…/TestLinux/bin/x64/Debug]
└─$

*/

如果没有tcsetpgrp(STDIN_FILENO, getpgrp()) == 0这里，该程序是不会stop的，只因为设置了改进程是前台，但是他属于后台了，so

shell 执行程序

ps -o pid,ppid,pgid,sid,comm | cat1 | cat2

PID PPID PGID SID COMMAND
949 947 949 949 sh
1988 949 949 949 cat2
1989 1988 949 949 ps
1990 1988 949 949 cat1