/*********************************************************************************
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* Copyright: (C) 2025 LingYun IoT System Studio
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* All rights reserved.
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*
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* Filename: mydaemon.c
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* Description: This file is daemon check example program
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*
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* Version: 1.0.0(11/07/2025)
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* Author: Guo Wenxue <guowenxue@gmail.com>
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* ChangeLog: 1, Release initial version on "11/07/2025 10:38:39 AM"
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*
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********************************************************************************/
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#include <stdio.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include <string.h>
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#include <errno.h>
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#include <signal.h>
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#include <sys/types.h>
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#define PID_FILE "/tmp/mydaemon.pid"
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/* 检查某个 pid 是否存在 */
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int is_process_running(pid_t pid)
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{
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if (pid <= 0)
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return 0;
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if (kill(pid, 0) == 0)
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{
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return 1; /* 进程存在且可访问 */
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}
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else
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{
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if (errno == ESRCH)
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return 0; /* 进程不存在 */
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else if (errno == EPERM)
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return 1; /* 存在但无权限 */
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else
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return 0; /* 其他错误 */
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}
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}
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/* 将当前进程 PID 写入文件 */
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int write_pid_file(const char *path)
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{
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FILE *fp;
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fp = fopen(path, "w");
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if (fp == NULL)
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{
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perror("fopen");
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return -1;
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}
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pid_t pid = getpid();
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fprintf(fp, "%d\n", pid);
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fclose(fp);
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return 0;
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}
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/* 从文件中读取 PID */
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pid_t read_pid_file(const char *path)
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{
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FILE *fp;
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pid_t pid = 0;
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fp = fopen(path, "r");
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if (fp == NULL)
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return 0;
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fscanf(fp, "%d", &pid);
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fclose(fp);
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return pid;
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}
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int main(void)
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{
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pid_t old_pid;
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old_pid = read_pid_file(PID_FILE);
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if (is_process_running(old_pid))
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{
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printf("Program is already running with PID %d.\n", old_pid);
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return 0;
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}
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/* 调用 daemon() 放入后台 */
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/*
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* daemon(int nochdir, int noclose)
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* nochdir = 0 表示切换到根目录 /
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* noclose = 0 表示关闭 stdin/stdout/stderr
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*/
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if (daemon(0, 0) < 0)
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{
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perror("daemon");
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exit(1);
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}
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/* 写入新的 PID 文件 */
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if (write_pid_file(PID_FILE) < 0)
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{
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fprintf(stderr, "Failed to write PID file.\n");
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exit(1);
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}
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/* 模拟后台工作 */
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while (1)
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{
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sleep(5); /* 这里可以换成自己的业务逻辑 */
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}
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return 0;
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}
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