UNIX编程(13)-守护进程
1.守护进程的编程规则
1）用umask将文件模式创建屏蔽字设置为0
2）调用fork,然后使父进程退出
3）调用setsid创建一个新会话
4）将当前工作目录更改为根目录
5）关闭不再需要的的文件描述符
6）某些守护进程打开/dev/null使其具有文件描述符0,1,2,
例：初始化一个守护进程
?
?
#include "apue.h"#include <syslog.h>#include <fcntl.h>#include <sys/resource.h>voiddaemonize(const char *cmd){ int i, fd0, fd1, fd2; pid_t pid; struct rlimit rl; struct sigaction sa; /* * Clear file creation mask. */ umask(0); /* * Get maximum number of file descriptors. */ if (getrlimit(RLIMIT_NOFILE, &rl) < 0) err_quit("%s: can't get file limit", cmd); /* * Become a session leader to lose controlling TTY. */ if ((pid = fork()) < 0) err_quit("%s: can't fork", cmd); else if (pid != 0) /* parent */ exit(0); setsid(); /* * Ensure future opens won't allocate controlling TTYs. */ sa.sa_handler = SIG_IGN; sigemptyset(&sa.sa_mask); sa.sa_flags = 0; if (sigaction(SIGHUP, &sa, NULL) < 0) err_quit("%s: can't ignore SIGHUP"); if ((pid = fork()) < 0) err_quit("%s: can't fork", cmd); else if (pid != 0) /* parent */ exit(0); /* * Change the current working directory to the root so * we won't prevent file systems from being unmounted. */ if (chdir("/") < 0) err_quit("%s: can't change directory to /"); /* * Close all open file descriptors. */ if (rl.rlim_max == RLIM_INFINITY) rl.rlim_max = 1024; for (i = 0; i < rl.rlim_max; i++) close(i); /* * Attach file descriptors 0, 1, and 2 to /dev/null. */ fd0 = open("/dev/null", O_RDWR); fd1 = dup(0); fd2 = dup(0); /* * Initialize the log file. */ openlog(cmd, LOG_CONS, LOG_DAEMON); if (fd0 != 0 || fd1 != 1 || fd2 != 2) { syslog(LOG_ERR, "unexpected file descriptors %d %d %d", fd0, fd1, fd2); exit(1); }}
2.出错记录
使用syslog设施产生日志
有三种方法产生日志信息：
1）内核调用log函数
2）调用syslog函数以产生日志消息
3）用网络程序发送到其他主机的514端口
?
syslogd守护进程读取三种格式的日志信息,此守护进程在启动时读一个配置文件，/etc/syslog.conf，该文件决定了不同种类的消息送向何处。
?
?4.守护进程的惯例
例：守护进程重新读配置文件
#include "apue.h"#include <pthread.h>#include <syslog.h>sigset_t mask;extern int already_running(void);voidreread(void){ /* ... */}void *thr_fn(void *arg){ int err, signo; for (;;) { err = sigwait(&mask, &signo); if (err != 0) { syslog(LOG_ERR, "sigwait failed"); exit(1); } switch (signo) { case SIGHUP: syslog(LOG_INFO, "Re-reading configuration file"); reread(); break; case SIGTERM: syslog(LOG_INFO, "got SIGTERM; exiting"); exit(0); default: syslog(LOG_INFO, "unexpected signal %d\n", signo); } } return(0);}intmain(int argc, char *argv[]){ int err; pthread_t tid; char *cmd; struct sigaction sa; if ((cmd = strrchr(argv[0], '/')) == NULL) cmd = argv[0]; else cmd++; /* * Become a daemon. */ daemonize(cmd); /* * Make sure only one copy of the daemon is running. */ if (already_running()) { syslog(LOG_ERR, "daemon already running"); exit(1); } /* * Restore SIGHUP default and block all signals. */ sa.sa_handler = SIG_DFL; sigemptyset(&sa.sa_mask); sa.sa_flags = 0; if (sigaction(SIGHUP, &sa, NULL) < 0) err_quit("%s: can't restore SIGHUP default"); sigfillset(&mask); if ((err = pthread_sigmask(SIG_BLOCK, &mask, NULL)) != 0) err_exit(err, "SIG_BLOCK error"); /* * Create a thread to handle SIGHUP and SIGTERM. */ err = pthread_create(&tid, NULL, thr_fn, 0); if (err != 0) err_exit(err, "can't create thread"); /* * Proceed with the rest of the daemon. */ /* ... */ exit(0);}?
另外一种实现
?
#include "apue.h"#include <syslog.h>#include <errno.h>extern int lockfile(int);extern int already_running(void);voidreread(void){ /* ... */}voidsigterm(int signo){ syslog(LOG_INFO, "got SIGTERM; exiting"); exit(0);}voidsighup(int signo){ syslog(LOG_INFO, "Re-reading configuration file"); reread();}intmain(int argc, char *argv[]){ char *cmd; struct sigaction sa; if ((cmd = strrchr(argv[0], '/')) == NULL) cmd = argv[0]; else cmd++; /* * Become a daemon. */ daemonize(cmd); /* * Make sure only one copy of the daemon is running. */ if (already_running()) { syslog(LOG_ERR, "daemon already running"); exit(1); } /* * Handle signals of interest. */ sa.sa_handler = sigterm; sigemptyset(&sa.sa_mask); sigaddset(&sa.sa_mask, SIGHUP); sa.sa_flags = 0; if (sigaction(SIGTERM, &sa, NULL) < 0) { syslog(LOG_ERR, "can't catch SIGTERM: %s", strerror(errno)); exit(1); } sa.sa_handler = sighup; sigemptyset(&sa.sa_mask); sigaddset(&sa.sa_mask, SIGTERM); sa.sa_flags = 0; if (sigaction(SIGHUP, &sa, NULL) < 0) { syslog(LOG_ERR, "can't catch SIGHUP: %s", strerror(errno)); exit(1); } /* * Proceed with the rest of the daemon. */ /* ... */ exit(0);}?