如何使用简单的Daemon C代码在Ubuntu 16.10中启动systemctl服务

Question

我写简单的C代码

#include<stdio.h>
#include<sys/types.h>
#include<stdlib.h>
#include<unistd.h>
#include <sys/stat.h>
int main(){

        pid_t pid;
        pid=fork();

        if(pid>0){

                exit(1);
        }



        FILE *fp;
        fp=fopen("pid.pid","a");
        fprintf(fp,"%d",getpid());
        fclose(fp);
        printf("\npid = %d\n",pid);
        printf("\ngetpid = %d\n",getpid());
        puts("\nAfter fclose() \n");
        umask(0);

        while(1){}

return 0;
}

还有Daemon1。服务

[Units]
Description=Socket programming with Daemon

[Service]
User=root
Type=forking
WorkingDirectory=/Omkar/Doc/systemctl/
ExecStart=/Omkar/Doc/systemctl/main
Restart=always
PIDFile=/Omkar/Doc/systemctl/pid.pid

[Install]
WantedBy=multi-user.target

并存放在

/etc/systemd/system

在此之后我运行命令

systemctl守护进程-重新加载

systemctl启用Daemon1。服务

System CTL start Daemon1.service

然后我得到了错误

Daemon1的工作。服务失败，因为控制进程已退出，错误代码为。

有关详细信息，请参阅“systemctl status Daemon1.service”和“journalctl xe”。

然后我用这个命令检查服务状态

systemctl状态Daemon1。服务

然后我得到了这个

● Daemon1.service
   Loaded: loaded (/etc/systemd/system/Daemon1.service; enabled; vendor preset: enabled)
   Active: failed (Result: start-limit-hit) since Tue 2019-11-19 18:21:26 IST; 3min 26s ago
  Process: 5868 ExecStart=/Omkar/Doc/systemctl/main (code=exited, status=1/FAILURE)

Nov 19 18:21:26 pt32-H81M-S systemd[1]: Failed to start Daemon1.service.
Nov 19 18:21:26 pt32-H81M-S systemd[1]: Daemon1.service: Unit entered failed state.
Nov 19 18:21:26 pt32-H81M-S systemd[1]: Daemon1.service: Failed with result 'exit-code'.
Nov 19 18:21:26 pt32-H81M-S systemd[1]: Daemon1.service: Service hold-off time over, scheduling restart.
Nov 19 18:21:26 pt32-H81M-S systemd[1]: Stopped Daemon1.service.
Nov 19 18:21:26 pt32-H81M-S systemd[1]: Daemon1.service: Start request repeated too quickly.
Nov 19 18:21:26 pt32-H81M-S systemd[1]: Failed to start Daemon1.service.
Nov 19 18:21:26 pt32-H81M-S systemd[1]: Daemon1.service: Unit entered failed state.
Nov 19 18:21:26 pt32-H81M-S systemd[1]: Daemon1.service: Failed with result 'start-limit-hit'.

我的服务没有运行。我需要修改什么才能让我的代码正常工作。我将C代码的可执行文件提供给Daemon1中的ExecStart=。服务

Answer 1

您的输出中有一行给出了一个不那么微妙的提示：（code=exited，status=1/FAILURE）

● Daemon1.service
   Loaded: loaded (/etc/systemd/system/Daemon1.service; enabled; vendor preset: enabled)
   Active: failed (Result: start-limit-hit) since Tue 2019-11-19 18:21:26 IST; 3min 26s ago
  Process: 5868 ExecStart=/Omkar/Doc/systemctl/main (code=exited, status=1/FAILURE)

修改您的代码在分叉后返回0而不是1到操作系统。

        if(pid>0){

                exit(0);
        }

在那次小小的调整之后，你应该重新开始工作，继续前进：

# systemctl status Daemon1.service
● Daemon1.service
   Loaded: loaded (/etc/systemd/system/Daemon1.service; enabled; vendor preset: enabled)
   Active: active (running) since Tue 2019-11-19 08:49:33 CST; 5s ago
  Process: 20484 ExecStart=/root/stackoverflow/Daemon1 (code=exited, status=0/SUCCESS)
 Main PID: 20486 (Daemon1)
   CGroup: /system.slice/Daemon1.service
           └─20486 /root/stackoverflow/Daemon1

Nov 19 08:49:33 lm systemd[1]: Starting Daemon1.service...
Nov 19 08:49:33 lm systemd[1]: Started Daemon1.service.