add daemonizing function; modify test of copy running

daemon.c

@@ -21,6 +21,7 @@
 
 #include <stdio.h>      // printf, fopen, ...
 #include <unistd.h>     // getpid
+#include <signal.h>
 #include <stdio.h>      // perror
 #include <sys/types.h>  // opendir
 #include <dirent.h>     // opendir
@@ -73,42 +74,19 @@ void WEAK sl_iffound_deflt(pid_t pid){
 /**
  * check wether there is a same running process
  * exit if there is a running process or error
- * Checking have 3 steps:
+ * Checking have 2 steps:
- *      1) lock executable file
+ *      1) check pidfile and its owner (if you run a copy?)
- *      2) check pidfile (if you run a copy?)
+ *      2) check /proc for executables with the same name (no/wrong pidfile)
- *      3) check /proc for executables with the same name (no/wrong pidfile)
+ * @param selfname - deprecated, maybe remove in next versions
- * @param selfname - argv[0] or NULL for non-locking
  * @param pidfilename - name of pidfile or NULL if none
  */
-void sl_check4running(char *selfname, char *pidfilename){
+void sl_check4running(char _U_ *selfname, char *pidfilename){
     DIR *dir;
-    FILE *pidfile, *fself;
+    FILE *pidfile;
     struct dirent *de;
     struct stat s_buf;
     pid_t pid = 0, self;
-    struct flock fl;
     char *name, *myname;
-    if(selfname){ // block self
-        fself = fopen(selfname, "r"); // open self binary to lock
-        if(!fself){
-            WARN("fopen()");
-            goto selfpid;
-        }
-        memset(&fl, 0, sizeof(struct flock));
-        fl.l_type = F_WRLCK;
-        if(fcntl(fileno(fself), F_GETLK, &fl) == -1){ // check locking
-            WARN("fcntl()");
-            goto selfpid;
-        }
-        if(fl.l_type != F_UNLCK){ // file is locking - exit
-            sl_iffound_deflt(fl.l_pid);
-        }
-        fl.l_type = F_RDLCK;
-        if(fcntl(fileno(fself), F_SETLKW, &fl) == -1){
-            WARN("fcntl()");
-        }
-    }
-    selfpid:
     self = getpid(); // get self PID
     if(!(dir = opendir(PROC_BASE))){ // open /proc directory
         ERR(PROC_BASE);
@@ -120,9 +98,11 @@ void sl_check4running(char *selfname, char *pidfilename){
     if(pidfilename && stat(pidfilename, &s_buf) == 0){ // pidfile exists
         pidfile = fopen(pidfilename, "r");
         if(pidfile){
-            if(fscanf(pidfile, "%d", &pid) > 0){ // read PID of (possibly) running process
+            if(fscanf(pidfile, "%d", &pid) == 1){ // read PID of (possibly) running process
-                if((name = sl_getPSname(pid)) && strncmp(name, myname, 255) == 0)
+                if((name = sl_getPSname(pid)) && strncmp(name, myname, 255) == 0){
                     sl_iffound_deflt(pid);
+                    exit(1); // run `exit` if user forgot to do it himself
+                }
             }
             fclose(pidfile);
         }
@@ -131,8 +111,10 @@ void sl_check4running(char *selfname, char *pidfilename){
     while((de = readdir(dir))){ // scan /proc
         if(!(pid = (pid_t)atoi(de->d_name)) || pid == self) // pass non-PID files and self
             continue;
-        if((name = sl_getPSname(pid)) && strncmp(name, myname, 255) == 0)
+        if((name = sl_getPSname(pid)) && strncmp(name, myname, 255) == 0){
             sl_iffound_deflt(pid);
+            exit(1);
+        }
     }
     closedir(dir);
     free(myname);
@@ -143,3 +125,24 @@ void sl_check4running(char *selfname, char *pidfilename){
         fclose(pidfile);
     }
 }
+
+/**
+ * @brief sl_daemonize - prepare for daemonize:
+ * - close stdin/out/err and reopen to /dev/null
+ * - croot /
+ * - umask(0)
+ * - ignore SIGHUP
+ * @return non-zero if failed
+ */
+int sl_daemonize(){
+    if(chdir("/")) return -1;
+    umask(0);
+    close(STDIN_FILENO);
+    close(STDOUT_FILENO);
+    close(STDERR_FILENO);
+    if(open("/dev/null", O_RDWR) < 0) return -1;
+    if(dup(0) < 0) return -1;
+    if(dup(0) < 0) return -1;
+    if(SIG_ERR == signal(SIGHUP, SIG_IGN)) return -1;
+    return 0;
+}

examples/CMakeLists.txt

@@ -14,3 +14,4 @@ add_executable(fifo fifo.c)
 add_executable(conffile conffile.c)
 add_executable(clientserver clientserver.c)
 add_executable(ringbuffer ringbuffer.c)
+add_executable(daemon daemon.c)

examples/daemon.c

@@ -0,0 +1,105 @@
+/*
+ * This file is part of the Snippets project.
+ * Copyright 2024 Edward V. Emelianov <edward.emelianoff@gmail.com>.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+// example of simplest daemon: search for running process, daemonize if all OK and herd its child
+
+#include <linux/prctl.h>
+#include <sys/prctl.h>
+#include <sys/wait.h>
+#include <usefull_macros.h>
+
+static pid_t childpid = 0;
+
+typedef struct{
+    int help;
+    int verbose;
+    int nodaemon;
+    char *logfile;
+    char *pidfile;
+} parameters;
+
+static parameters G = {0};
+
+static sl_option_t cmdlnopts[] = {
+    {"help",        NO_ARGS,    NULL,   'h',    arg_int,    APTR(&G.help),      "show this help"},
+    {"verbose",     NO_ARGS,    NULL,   'v',    arg_none,   APTR(&G.verbose),   "verbose level (each -v adds 1)"},
+    {"logfile",     NEED_ARG,   NULL,   'l',    arg_string, APTR(&G.logfile),   "log file name (FULL path!!!)"},
+    {"pidfile",     NEED_ARG,   NULL,   'p',    arg_string, APTR(&G.pidfile),   "PID-file name (FULL path!!!)"},
+    {"nodaemon",    NO_ARGS,    NULL,   0,      arg_int,    APTR(&G.nodaemon),  "don't daemonize"},
+    end_option
+};
+
+void sl_iffound_deflt(pid_t pid){
+    WARNX("Another copy of this process found, pid=%d. Exit.", pid);
+    exit(1); // don't run `signals` to protect foreign PID-file from removal
+}
+
+void signals(int signo){
+    if(childpid){ // this is a main process!
+        LOGERR("Main process exits with status %d", signo);
+        // main process have nothing to cleanup, just remove PID-file
+        if(G.pidfile) unlink(G.pidfile);
+    }else{ // this is child
+        LOGERR("Killed with status %d, clearing", signo);
+        // here we can close everything and make cleanup
+    }
+    usleep(1000);
+    LOGERR("Exited");
+    exit(signo);
+}
+
+int main(int argc, char **argv){
+    sl_init();
+    sl_parseargs(&argc, &argv, cmdlnopts);
+    if(G.help) sl_showhelp(-1, cmdlnopts);
+    sl_loglevel_e lvl = G.verbose + LOGLEVEL_ERR;
+    if(lvl >= LOGLEVEL_AMOUNT) lvl = LOGLEVEL_AMOUNT - 1;
+    sl_check4running(NULL, G.pidfile);
+    LOGMSG("Hello, I'm started");
+    if(G.logfile) OPENLOG(G.logfile, lvl, 1);
+    if(!G.nodaemon){
+        green("Daemonize..\n");
+        LOGMSG("Daemonize");
+        // and ignore SIGHUP
+        if(sl_daemonize()){
+            WARN("sl_daemonize() failed");
+            LOGERR("Can't daemonize");
+        }
+    }
+    signal(SIGTERM, signals); // kill (-15) - quit
+    signal(SIGINT, signals);  // ctrl+C - quit
+    signal(SIGQUIT, signals); // ctrl+\ - quit
+    signal(SIGTSTP, SIG_IGN); // ignore ctrl+Z
+    while(1){ // guard for dead processes
+        childpid = fork();
+        if(childpid){
+            LOGMSG("create child with PID %d\n", childpid);
+            DBG("Created child with PID %d\n", childpid);
+            wait(NULL);
+            WARNX("Child %d died\n", childpid);
+            LOGWARN("Child %d died\n", childpid);
+            sleep(1);
+        }else{
+            prctl(PR_SET_PDEATHSIG, SIGTERM); // send SIGTERM to child when parent dies
+            break; // go out to normal functional
+        }
+    }
+    LOGMSG("Here is the child process; sleep for 1 second and die");
+    sleep(1);
+    return 0;
+}

usefull_macros.h

@@ -329,6 +329,8 @@ void WEAK sl_iffound_deflt(pid_t pid);
 void sl_check4running(char *selfname, char *pidfilename);
 // read name of process by its PID
 char *sl_getPSname(pid_t pid);
+// daemonize: reopen stdin/out/err as /dev/null, chdir to /, umask(0)
+int sl_daemonize(); // return -1 if failed, 0 on OK
 
 /******************************************************************************\
                          The original fifo_lifo.h