linux
cron,at
crontab文件的存放路径是/etc/crontab
cron用来执行周期性的事件，cron命令有个一个特殊的文件与之对应，内容如下[oracle@golonglee spool]$ cat /etc/crontab SHELL=/bin/bashPATH=/sbin:/bin:/usr/sbin:/usr/binMAILTO=rootHOME=/# For details see man 4 crontabs# Example of job definition:# .---------------- minute (0 - 59)# | .------------- hour (0 - 23)# | | .---------- day of month (1 - 31)# | | | .------- month (1 - 12) OR jan,feb,mar,apr ...# | | | | .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat# | | | | |# * * * * * user-name command to be executed[oracle@golonglee spool]$
Linux的启动模式可通过inittab文件进行配置，下面是inittab文件的内容# cat /etc/inittab # inittab is only used by upstart for the default runlevel.## ADDING OTHER CONFIGURATION HERE WILL HAVE NO EFFECT ON YOUR SYSTEM.## System initialization is started by /etc/init/rcS.conf## Individual runlevels are started by /etc/init/rc.conf## Ctrl-Alt-Delete is handled by /etc/init/control-alt-delete.conf## Terminal gettys are handled by /etc/init/tty.conf and /etc/init/serial.conf,# with configuration in /etc/sysconfig/init.## For information on how to write upstart event handlers, or how# upstart works, see init(5), init(8), and initctl(8).## Default runlevel. The runlevels used are:# 0 - halt (Do NOT set initdefault to this)# 1 - Single user mode# 2 - Multiuser, without NFS (The same as 3, if you do not have networking)# 3 - Full multiuser mode# 4 - unused# 5 - X11# 6 - reboot (Do NOT set initdefault to this)# id:5:initdefault:# 这里的【id:5:initdefault:】就是说本系统默认是以X11也就是x-window的模式启动。
Runlevel 0 ——init关闭所有进程并终止系统。Runlevel 1 ——转到单用户模式Runlevel 2 ——进入多用户的模式Runlevel 3 ——多用户模式，也是多数服务器的默认模式。Runlevel 4 —— 一般不使用，可以实现一些特定的登录请求。Runlevel 5 ——X Window终端。Runlevel 6 ——是关闭进程并重新启动系统。
/etc/rc开头的文件，一般都是系统启动后自动执行的文件。rc开头的文件很多，如下：rc rc1.d/ rc3.d/ rc5.d/ rc.d/ rc.sysinitrc0.d/ rc2.d/ rc4.d/ rc6.d/ rc.local其中init是所有进程之父 init读取/etc/inittab，执行rc.sysinit脚本
运行顺序由inittab中设置的init tree决定，一般设置为： /etc/rc.d/rc0.d /etc/rc.d/rc1.d /etc/rc.d/rc2.d /etc/rc.d/rc3.d /etc/rc.d/rc4.d /etc/rc.d/rc5.d /etc/rc.d/rc6.d /etc/rc.d/rc.local其中/etc/rc.d/rc.local默认是用户自定义的脚本
/etc/rc.d/rc.local文件内容如下：[root@golonglee etc]# cat /etc/rc.local #!/bin/sh## This script will be executed *after* all the other init scripts.# You can put your own initialization stuff in here if you don't# want to do the full Sys V style init stuff.touch /var/lock/subsys/local经常使用的 rc.local 则完全是习惯问题，不是标准。不过使用 rc.local是个好习惯。