Daemon linux - Revision history

Heth at 04:07, 22 December 2022

2022-12-22T04:07:56Z

2022-12-20T12:39:25Z

‎Checking the daemon

2022-12-20T12:21:42Z

2022-12-20T12:18:31Z

2022-12-17T06:31:52Z

‎Checking the daemon

2022-12-17T06:31:34Z

‎Checking the daemon

2022-12-17T06:28:33Z

2022-12-17T06:27:26Z

2022-12-17T05:59:00Z

‎Checking the daemon

2022-12-16T06:49:03Z

@@ Line 1: / Line 1: @@
-=Creating a daemon with systemd=
 =Creating your own daemon=
 <onlyinclude>
-Example of creating a daemon in Linux:
+Example of creating a daemon in Linux: (See [[systemd debian]] for systemd daemons)
 *'''setsid()''' - damon will be the session leader. Sets Session ID (SID) and Group ID (GID) to Process ID (PID)
 *Reopening stdin, stdout and stderr to /dev/null detaches the process from the controlling terminal and Parent PID is set to 1 (init or systemd - depending on Linux version/distribution)

@@ Line 55: / Line 55: @@
 USER         PID    PPID    PGID     SID TTY       COMMAND
 heth      778254       1  778254  778254 ?        my_daemon
+$ tail -f /var/log/sysg
 </source>
 </onlyinclude>
 [[Category:Linux]]

@@ Line 1: / Line 1: @@
 =Creating a daemon with systemd=
 =Creating your own daemon=
 Example of creating a daemon in Linux:
 *'''setsid()''' - damon will be the session leader. Sets Session ID (SID) and Group ID (GID) to Process ID (PID)
@@ Line 56: / Line 57: @@
 </source>
 [[Category:Linux]]

← Older revision		Revision as of 12:18, 20 December 2022
Line 1:		Line 1:
		+	=Creating a daemon with systemd=
		+	=Creating your own daemon=
	Example of creating a daemon in Linux:		Example of creating a daemon in Linux:
	*'''setsid()''' - damon will be the session leader. Sets Session ID (SID) and Group ID (GID) to Process ID (PID)		*'''setsid()''' - damon will be the session leader. Sets Session ID (SID) and Group ID (GID) to Process ID (PID)

@@ Line 46: / Line 46: @@
 </source>
 ===Checking the daemon===
-Daemon detached from TTY - PPID is 1
+*Daemon detached from TTY - PPID is 1
-Session and session group leader - SID and PGID same as PID
+* Session and session group leader - SID and PGID same as PID
 <source lang=bash>
 $ ps xo uname,pid,ppid,pgid,sid,tty,comm | grep -P '(my_daemon|COMMAND)'

@@ Line 8: / Line 8: @@
 #include <stdlib.h>
 #include <syslog.h>
 void  daemon_create(void);
 int main(void) {
          printf("Starting my_daemon\n");
          openlog("my_daemon", LOG_INFO, LOG_DAEMON);
          daemon_create();
          for (int i=0; i < 100; i++) {
                  syslog(LOG_INFO,"Countet to %d", i);
@@ Line 33: / Line 29: @@
          exit(1);
+     }
-     if(pid > 0){
+     if(pid > 0) {
          syslog(LOG_INFO, "Parent dying");
          exit(0); // Parent die
@@ Line 46: / Line 42: @@
                  syslog(LOG_ERR, "When creating daemon freopen from STDIN/OUT/ERR failed: %m");
                  exit(3);
+    }
+}

@@ Line 2: / Line 2: @@
 *'''setsid()''' - damon will be the session leader. Sets Session ID (SID) and Group ID (GID) to Process ID (PID)
 *Reopening stdin, stdout and stderr to /dev/null detaches the process from the controlling terminal and Parent PID is set to 1 (init or systemd - depending on Linux version/distribution)
 <source lang=c line>
 void  daemon_create(void) {
      pid_t pid;
@@ Line 10: / Line 30: @@
      pid = fork();
      if(pid < 0){
-         log_err("Error in fork: %m");  // Write error to terminal
+         syslog(LOG_ERR, "Error in fork: %m");
          exit(1);
+     }
      if(pid > 0){
          exit(0); // Parent die
+     }
      if(setsid() < 0){ // Make child session leader
-         log_err("Error in setsid: %m");
+         syslog(LOG_ERR, "Error in setsid: %m");
-         exit(1);
+         exit(2);
+         }
-         if (   freopen("/dev/null", "r", stdin) == NULL
+         if (freopen("/dev/null", "r", stdin) == NULL
          || freopen("/dev/null", "w", stdout) == NULL
          || freopen("/dev/null", "w", stderr) == NULL ) {
-                 log_err("When creating daemon freopen from STDIN/OUT/ERR failed: %m");
+                 syslog(LOG_ERR, "When creating daemon freopen from STDIN/OUT/ERR failed: %m");
+                exit(3);
-        log_to_syslog(); // Log to syslog only when in daemon mode
+}
 </source>

@@ Line 34: / Line 34: @@
        1  772175  772175 my_daemon
 </source>
-{{Category:Linux]]
+[[Category:Linux]]