ubuntu下shutdown命令详解

shutdown(8) System Manager’s Manual shutdown(8)

NAME
shutdown - bring the system down

SYNOPSIS
shutdown [OPTION]… TIME [MESSAGE]

DESCRIPTION
shutdown arranges for the system to be brought down in a safe way. All
logged-in users are notified that the system is going down and, within
the last five minutes of TIME, new logins are prevented.

   TIME  may  have  different  formats, the most common is simply the word   'now' which will bring the system down immediately.  Other  valid  for‐   mats  are  +m,  where m is the number of minutes to wait until shutting   down and hh:mm which specifies the time on the 24hr clock.   If no option is specified, the default action is to  bring  the  system   down into single-user mode.   Once  TIME  has elapsed, shutdown sends a request to the init(8) daemon   to bring the system down into the appropriate runlevel.   This is performed by emitting the runlevel(7) event, which includes the   new runlevel in the RUNLEVEL environment variable as well as the previ‐   ous runlevel (obtained from the environment or from  /var/run/utmp)  in   the  PREVLEVEL  variable.  An additional INIT_HALT variable may be set,   this will contain the value HALT when bringing the system down for halt   and POWEROFF when bringing the system down for power off.

OPTIONS
-r Requests that the system be rebooted after it has been brought
down.

   -h     Requests that the system be either halted or powered  off  after          it has been brought down, with the choice as to which left up to          the system.   -H     Requests that the system be halted after  it  has  been  brought          down.   -P     Requests  that  the  system  be  powered  off  after it has been          brought down.   -c     Cancels a running shutdown.  TIME is  not  specified  with  this          option, the first argument is MESSAGE.   -k     Only  send  out  the warning messages and disable logins, do not          actually bring the system down.

ENVIRONMENT
RUNLEVEL
shutdown will read the current runlevel from this environment
variable if set in preference to reading from /var/run/utmp

FILES
/var/run/utmp
Where the current runlevel will be read from; this file will
also be updated with the new runlevel.

   /var/log/wtmp          A new runlevel record will be appended to this file for the  new          runlevel.

NOTES
The Upstart init(8) daemon does not keep track of runlevels itself,
instead they are implemented entirely by its userspace tools.

   See runlevel(7) for more details.

AUTHOR
Written by Scott James Remnant [e-mail]

REPORTING BUGS
Report bugs at https://launchpad.net/upstart/+bugs

COPYRIGHT
Copyright © 2009 Canonical Ltd.
This is free software; see the source for copying conditions. There is
NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
PURPOSE.

SEE ALSO
runlevel(7) init(8) telinit(8) reboot(8)

Upstart 2009-07-09 shutdown(8)

以上为man shutdown 手册信息。下面看点中文的。

关机命令 shutdown

　　好像ubuntu的终端中默认的是当前用户的命令，只是普通用户，因此在终端器中可以使用sudo -sh 转换到管理员root用户下执行命令。

　　1)shutdown –help

　　可以查看shutdown命令如何使用，当然也可以使用man shutdown命令。

　　2) shutdown -h now 现在立即关机

　　3)shutdown -r now 现在立即重启

　　4)shutdown -r +3 三分钟后重启

　　5)shutdown -h +3 “The System will shutdown after 3 minutes” 提示使用者将在三分钟后关机

　　6)shutdown -r 20:23 在20：23时将重启计算机

　　7)shutdown -r 20:23 & 可以将在20：23时重启的任务放到后台去，用户可以继续操作终端

　　2中断命令

　　1)执行完命令后(若没有转到后台)，可以使用CTRL+C来中止命令

　　2)kill 程序编码

　　当命令在后台执行时系统会返回一个程序编码，例如：在使用 shutdown -r 20:23 & 系统返回系统编码：4905

　　我们可以使用kill 4905来中止重启命令

　　3ps aux | grep 程序编号

　　我们如果知道程序的编号，我们可以使用ps aux |grep 程序编号来查询该程序编号对应的命令是什么。

　　例如上面的程序编号为4905 ，我们可以使用ps aux | grep 4905 就可以查到 shutdown -r 20:23 & 的命令

　　halt—-最简单的关机命令

　　其实halt就是调用shutdown -h。halt执行时﹐杀死应用进程﹐执行sync系统调用﹐文件系统写操作完成后就会停止内核。

　　参数说明:

　　[-n] 防止sync系统调用﹐它用在用fsck修补根分区之后﹐以阻止内核用老版本的超级块〔superblock〕覆盖修补过的超级块。

　　[-w] 并不是真正的重启或关机﹐只是写wtmp〔/var/log/wtmp〕纪录。

　　[-d] 不写wtmp纪录〔已包含在选项[-n]中〕。

　　[-f] 没有调用shutdown而强制关机或重启。

　　[-i] 关机〔或重启〕前﹐关掉所有的网络接口。

　　[-p] 该选项为缺省选项。就是关机时调用poweroff。