如何使用简单的守护程序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;
}

以及 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

并存储在以下位置

/etc/systemd/system

执行此操作后，我运行以下命令

systemctl daemon-reload

systemctl enable Daemon1.service

systemctl start Daemon1.service

然后我遇到了错误

Daemon1.service的作业失败，因为控制进程以错误代码退出。

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

然后我使用此命令检查服务的状态

systemctl status Daemon1.service

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。我需要更改什么以便我的代码能够工作。 我将 C 代码的可执行文件提供给 Daemon1.service 中的 ExecStart=。

- Omkar

Answer 1

你的输出中有一行给出了一个不太明显的提示：(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)

在分叉后，修改您的代码以返回 0 而不是 1 给操作系统。

        if(pid>0){

                exit(0);
        }

在进行了这个小调整之后，您应该能够继续业务了：

# 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.

- vhoang

---

非常感谢 @Viet Hoang。我卡了4个小时，试验了很多可执行文件。非常感谢！我已经得到了答案。 - Omkar