linux基礎學習（1）

切換X WINDOWN 與命令列模式
ctrl+alt+(F1-F6) 命令模式,default linux提供6個終端讓使用者登入(tty1-tty6)
ctrl+alt+F7 切換到圖形介面
另外在命令模式如果ctrl+alt+f7預設沒東西不是圖形介面
可以執行startx

命令登入
[root@xhlinux ~]#
分析root表示username,root在linux就是supper user,xhlinux HOSTNAME
[root@xhlinux ~]# hostname
xhlinux
~:是一個變數表示使用者的主資料夾，例如root主資料夾 /root，~就=/root
另外在linux中 root default提示符為#,一般身份user提示符為$
[root@xhlinux ~]# exit
logout
退出，登出(登入只是一個作業，登出時該作業停止，其他作業還可以執行)

linux命令執行:語法[root@xhlinux ~]# command [- option] parameter1 parameter2
分析:command :為命令名稱，例如cd,rm,ls等
[- option]: 加入引數時設定一般為 -號，比如-h,完整的引數名稱輸入--符號,例如--help
parameter 1..2：是在-options或command後面的引數
command [- option] parameter1：中間以空格區分,不論中間幾個空格,shell都視作一格(簡單說shell為linux提供給user一些工具,可以控制核心動作)
[root@xhlinux ~]# ls -al /root
total 332
drwxr-x--- 15 root root 4096 Oct 19 21:09 .
drwxr-xr-x 23 root root 4096 Oct 19 20:58 ..
-rw-r--r--   1 root root 1173 Aug 16 23:40 anaconda-ks.cfg
..........................................
[root@xhlinux ~]# ls -al      /root
total 332
drwxr-x--- 15 root root 4096 Oct 19 21:09 .
drwxr-xr-x 23 root root 4096 Oct 19 20:58 ..
-rw-r--r--   1 root root 1173 Aug 16 23:40 anaconda-ks.cfg
-
.....................................
可以看到linux視為一個空格

但大小寫卻不一樣
[root@xhlinux ~]# date
Mon Oct 19 21:35:12 CST 2009
[root@xhlinux ~]# DATA
-bash: DATA: command not found
[root@xhlinux ~]#
比如VTEST與vtest在linux中是2個完全不一樣的檔案

基本命令:
[root@xhlinux ~]# date
Mon Oct 19 21:36:19 CST 2009
檢視當前時間

加上一些引數
[root@xhlinux ~]# date +%y/%m/%d
09/10/19

[root@xhlinux ~]# date +%H:%M
21:37
[root@xhlinux ~]# date +%h:%m
Oct:10
可以看到引數大小寫是完全不同的 2個命令

[root@xhlinux ~]# cal 顯示日曆
October 2009
Su Mo Tu We Th Fr Sa
1 2 3
4 5 6 7 8 9 10
11 12 13 14 15 16 17
18 19 20 21 22 23 24
25 26 27 28 29 30 31

[root@xhlinux ~]# cal 2009
2009

       January               February                 March
Su Mo Tu We Th Fr Sa   Su Mo Tu We Th Fr Sa   Su Mo Tu We Th Fr Sa
             1 2 3    1 2 3 4 5 6 7    1 2 3 4 5 6 7
4 5 6 7 8 9 10    8 9 10 11 12 13 14    8 9 10 11 12 13 14
11 12 13 14 15 16 17   15 16 17 18 19 20 21   15 16 17 18 19 20 21
18 19 20 21 22 23 24   22 23 24 25 26 27 28   22 23 24 25 26 27 28
25 26 27 28 29 30 31                          29 30 31

        April                   May                   June
Su Mo Tu We Th Fr Sa   Su Mo Tu We Th Fr Sa   Su Mo Tu We Th Fr Sa
          1 2 3 4                   1 2       1 2 3 4 5 6
5 6 7 8 9 10 11    3 4 5 6 7 8 9    7 8 9 10 11 12 13
12 13 14 15 16 17 18   10 11 12 13 14 15 16   14 15 16 17 18 19 20
19 20 21 22 23 24 25   17 18 19 20 21 22 23   21 22 23 24 25 26 27
26 27 28 29 30         24 25 26 27 28 29 30   28 29 30
                       31
        July                  August                September
Su Mo Tu We Th Fr Sa   Su Mo Tu We Th Fr Sa   Su Mo Tu We Th Fr Sa
          1 2 3 4                      1          1 2 3 4 5
5 6 7 8 9 10 11    2 3 4 5 6 7 8    6 7 8 9 10 11 12
12 13 14 15 16 17 18    9 10 11 12 13 14 15   13 14 15 16 17 18 19
19 20 21 22 23 24 25   16 17 18 19 20 21 22   20 21 22 23 24 25 26
26 27 28 29 30 31      23 24 25 26 27 28 29   27 28 29 30
                       30 31
       October               November               December
Su Mo Tu We Th Fr Sa   Su Mo Tu We Th Fr Sa   Su Mo Tu We Th Fr Sa
             1 2 3    1 2 3 4 5 6 7          1 2 3 4 5
4 5 6 7 8 9 10    8 9 10 11 12 13 14    6 7 8 9 10 11 12
11 12 13 14 15 16 17   15 16 17 18 19 20 21   13 14 15 16 17 18 19
18 19 20 21 22 23 24   22 23 24 25 26 27 28   20 21 22 23 24 25 26
25 26 27 28 29 30 31   29 30                  27 28 29 30 31

[root@xhlinux ~]# cal 9 2009
September 2009
Su Mo Tu We Th Fr Sa
1 2 3 4 5
6 7 8 9 10 11 12
13 14 15 16 17 18 19
20 21 22 23 24 25 26
27 28 29 30
可以看到cal命令語法為cal month year

計算器:BC
[root@xhlinux ~]# bc
bc 1.06
Copyright 1991-1994, 1997, 1998, 2000 Free Software Foundation, Inc.
This is free software with ABSOLUTELY NO WARRANTY.
For details type `warranty'.

1+2
3
1*100
100
10/100~~~~~10/100應該為0.1而卻輸出了0，因為bc計算器default輸出整數，要輸出小數點後的需要scale=number(小數點後幾位)
0

scale=3
10/100
.100

quit~~~~~~~~~~~~~退出
[root@xhlinux ~]#

重要的熱鍵:
TAB:具有命令補全，檔案補全的功能

[root@xhlinux ~]# ca（ca後按2次tab 列出所有ca開頭的命令）
cacertdir_rehash    callgrind_control   card
cadaver             cancel              cardctl
cal                 cancel.cups         cardmgr
calibrate_ppa       capifax             case
callback            capifaxrcvd         cat
caller              capiinfo            catchsegv
callgrind           capiinit
callgrind_annotate captoinfo

[root@xhlinux ~]# ls -al ~/.bash
ls: /root/.bash: No such file or directory

[root@xhlinux ~]# ls -al ~/.bash（2次tab）
.bash_history .bash_logout   .bash_profile .bashrc

所有以.bash的檔名都會顯示出來   ，如果按tab在命令後（例如:ca 後）那麼為命令補全,如果在第2個字以後 (例中在.bash後)表示檔案補齊

ctrl+c：中斷當前操作立刻終止

ctrl_d:表示輸出結束，等於輸入exit
[root@xhlinux ~]# bc
bc 1.06
Copyright 1991-1994, 1997, 1998, 2000 Free Software Foundation, Inc.
This is free software with ABSOLUTELY NO WARRANTY.
For details type `warranty'.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~按ctrl+d
[root@xhlinux ~]# ～～～～～～～～～～～～退出

錯誤資訊：
[root@xhlinux ~]# DATE
-bash: DATE: command not found
[root@xhlinux ~]# cal 13 2009
cal: illegal month value: use 1-12
linux的錯誤資訊寫的非常直觀可以直接看

關於linux的所有命令
[root@xhlinux ~]# 按2次tab
[root@xhlinux ~]#
Display all 2684 possibilities? (y or n) 是否顯示 2684個命令
c2ph
c89
c99
cacertdir_rehash
cadaver
cal
calibrate_ppa
callback
caller
callgrind
callgrind_annotate
callgrind_control
cancel
cancel.cups
capifax
capifaxrcvd
capiinfo
capiinit
captoinfo
--More--
captoinfo
[root@xhlinux ~]# 可以看到有很多 ctrl+c 立即終止操作,只看下大概就可以

2684個命令如何記憶使用:
檢視幫助檔案 linux提供:man page/info page

[[root@xhlinux ~]# man date
DATE(1) User Commands DATE(1)

NAME
date - print or set the system date and time

SYNOPSIS
date [OPTION]... [+FORMAT]
date [-u|--utc|--universal] [MMDDhhmm[[CC]YY][.ss]]

DESCRIPTION
Display the current time in the given FORMAT, or set the system date.

-d, --date=STRING
display time described by STRING, not 'now'

-f, --file=DATEFILE
like --date once for each line of DATEFILE

       -ITIMESPEC, --iso-8601[=TIMESPEC]
              output date/time in ISO 8601 format. TIMESPEC='date' for date
              only, 'hours', 'minutes', or 'seconds' for date and time to the
              indicated precision. --iso-8601 without TIMESPEC defaults to
              'date'.

-r, --reference=FILE
display the last modification time of FILE

-R, --rfc-2822
output RFC-2822 compliant date string

-s, --set=STRING
set time described by STRING

-u, --utc, --universal
print or set Coordinated Universal Time

--help display this help and exit

--version
output version information and exit

FORMAT controls the output. The only valid option for the second form
specifies Coordinated Universal Time. Interpreted sequences are:

%% a literal %

%a locale's abbreviated weekday name (Sun..Sat)

%A locale's full weekday name, variable length (Sunday..Saturday)

%b locale's abbreviated month name (Jan..Dec)

%B locale's full month name, variable length (January..December)

%c locale's date and time (Sat Nov 04 12:02:33 EST 1989)

%C century (year divided by 100 and truncated to an integer)
[00-99]

%d day of month (01..31)

%D date (mm/dd/yy)

%e day of month, blank padded ( 1..31)

%F same as %Y-%m-%d

%g the 2-digit year corresponding to the %V week number

%G the 4-digit year corresponding to the %V week number

%h same as %b

%H hour (00..23)

%I hour (01..12)

%j day of year (001..366)

%k hour ( 0..23)

%l hour ( 1..12)

%m month (01..12)

%M minute (00..59)

%n a newline

%N nanoseconds (000000000..999999999)

%p locale's upper case AM or PM indicator (blank in many locales)

%P locale's lower case am or pm indicator (blank in many locales)

%r time, 12-hour (hh:mm:ss [AP]M)

%R time, 24-hour (hh:mm)

%s seconds since '00:00:00 1970-01-01 UTC' (a GNU extension)

%S second (00..60); the 60 is necessary to accommodate a leap sec-
ond

%t a horizontal tab

%T time, 24-hour (hh:mm:ss)

%u day of week (1..7); 1 represents Monday

%U week number of year with Sunday as first day of week (00..53)

%V week number of year with Monday as first day of week (01..53)

%w day of week (0..6); 0 represents Sunday

%W week number of year with Monday as first day of week (00..53)

%x locale's date representation (mm/dd/yy)

%X locale's time representation (%H:%M:%S)

%y last two digits of year (00..99)

%Y year (1970...)

%z RFC-2822 style. numeric timezone (-0500) (a nonstandard exten-
sion)

%Z time zone (e.g., EDT), or nothing if no time zone is deter-
minable

By default, date pads numeric fields with zeroes. GNU date recognizes
the following modifiers between '%' and a numeric directive.

'-' (hyphen) do not pad the field '_' (underscore) pad the
field with spaces

ENVIRONMENT
       TZ     Specifies the timezone, unless overridden by command line
              parameters.    If   neither is specified, the setting from
              /etc/localtime is used.

AUTHOR
Written by David MacKenzie.

REPORTING BUGS
Report bugs to <bug-coreutils@gnu.org>.

COPYRIGHT
       Copyright (C) 2004 Free Software Foundation, Inc.
       This is free software; see the source for copying conditions.   There
       is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICU-
       LAR PURPOSE.

SEE ALSO
       The full documentation for date is maintained as a Texinfo manual. If
       the info and date programs are properly installed at your site, the
       command

info coreutils date

should give you access to the complete manual.

date (coreutils) 5.2.1 March 2004 DATE(1)
(END)

可以看到 date命令的完整使用介紹

[root@xhlinux ~]# 按q 退出結束rman page
PAGE DOWN &空格下一頁,page up上一頁,home 第一頁,end最後一頁
/ 字串向下搜尋，?字串向上搜尋例如（搜尋 XH /xh,or ？xh, ）
n,N 使用 ?/搜尋字元時搭配使用 n繼續向下查詢,N往上查詢 ,比如?xh 向上查xh字元然後按N 那麼繼續向上查xh字元

man page 的資料一般存在/usr/share/man目錄

[root@xhlinux ~]# ls -al /usr/share/man
total 600
drwxr-xr-x   39 root root   4096 Aug 16 23:21 .
drwxr-xr-x 207 root root   4096 Aug 16 23:39 ..
drwxr-xr-x    4 root root   4096 Nov 17 2007 bg
drwxr-xr-x    4 root root   4096 Nov 17 2007 cs
drwxr-xr-x    4 root root   4096 Nov 17 2007 da
drwxr-xr-x    5 root root   4096 Nov 17 2007 de
drwxr-xr-x    5 root root   4096 Nov 17 2007 el
drwxr-xr-x    9 root root   4096 Nov 17 2007 en
drwxr-xr-x    4 root root   4096 Nov 17 2007 es
drwxr-xr-x    4 root root   4096 Nov 17 2007 fi
drwxr-xr-x    5 root root   4096 Nov 17 2007 fr
drwxr-xr-x    4 root root   4096 Nov 17 2007 hr
drwxr-xr-x    3 root root   4096 Aug 16 23:20 hu
drwxr-xr-x    3 root root   4096 Aug 16 23:20 id
drwxr-xr-x    5 root root   4096 Nov 17 2007 it
drwxr-xr-x    5 root root   4096 Nov 17 2007 ja
drwxr-xr-x    4 root root   4096 Nov 17 2007 ko
drwxr-xr-x    2 root root   4096 Aug 16 23:21 man0p
drwxr-xr-x    2 root root 53248 Aug 16 23:38 man1
drwxr-xr-x    2 root root   4096 Aug 16 23:21 man1p
drwxr-xr-x    2 root root 16384 Aug 16 23:33 man2
drwxr-xr-x    2 root root 167936 Aug 16 23:38 man3
drwxr-xr-x    2 root root 40960 Aug 16 23:21 man3p
drwxr-xr-x    2 root root   4096 Aug 16 23:29 man4
drwxr-xr-x    2 root root 12288 Aug 16 23:38 man5
drwxr-xr-x    2 root root   4096 Aug 16 23:21 man6
drwxr-xr-x    2 root root   4096 Aug 16 23:38 man7
drwxr-xr-x    2 root root 20480 Aug 16 23:38 man8
drwxr-xr-x    2 root root   4096 Feb 22 2005 man9
drwxr-xr-x    2 root root   4096 Feb 22 2005 mann
drwxr-xr-x    4 root root   4096 Nov 17 2007 nl
drwxr-xr-x    5 root root   4096 Nov 17 2007 pl
drwxr-xr-x    5 root root   4096 Nov 17 2007 pt
drwxr-xr-x    5 root root   4096 Aug 16 23:20 pt_BR
drwxr-xr-x    5 root root   4096 Nov 17 2007 ro
drwxr-xr-x    3 root root   4096 Aug 16 23:20 ru
drwxr-xr-x    3 root root   4096 Aug 16 23:20 sk
drwxr-xr-x    4 root root   4096 Nov 17 2007 sl
drwxr-xr-x    3 root root   4096 Aug 16 23:21 sv

可以修改man page搜尋路徑來改變這個目錄,修改/etc/man.config(man.conf,manpath.conf 不同版本)
[root@xhlinux ~]# ls -al /etc/man.config
-rw-r--r-- 1 root root 4522 Nov 17 2007 /etc/man.config

[root@xhlinux ~]# man man (檢視man的更多使用方法)
man: No such file or directory
Failed to open the message catalog man on the path NLSPATH=

Formatting page, please wait...
man(1) man(1)

NAME
man - format and display the on-line manual pages

SYNOPSIS
man [-acdfFhkKtwW] [--path] [-m system] [-p string] [-C config_file]
[-M pathlist] [-P pager] [-S section_list] [section] name ...

DESCRIPTION
       man formats and displays the on-line manual pages.   If you specify
       section, man only looks in that section of the manual. name is nor-
       mally the name of the manual page, which is typically the name of a
       command, function, or file.   However, if name contains a slash (/)
       then man interprets it as a file specification, so that you can do man
       ./foo.5 or even man /cd/foo/bar.1.gz.

See below for a description of where man looks for the manual page
files.

OPTIONS
       -C config_file
              Specify the configuration file to use; the   default   is
              /etc/man.config. (See man.config(5).)

       -M path
              Specify the list of directories to search for man pages. Sepa-
              rate the directories with colons. An empty list is the same as
              not specifying -M at all. See SEARCH PATH FOR MANUAL PAGES.

       -P pager
              Specify which pager to use. This option overrides the MANPAGER
              environment variable, which in turn overrides the PAGER vari-
              able. By default, man uses /usr/bin/less -iRs.

       -S section_list
              List is a colon separated list of manual sections to search.
              This option overrides the MANSECT environment variable.

       -a     By default, man will exit after displaying the first manual
              page it finds. Using this option forces man to display all the
              manual pages that match name, not just the first.

-b Disable any reference to color in the roff source. NOCOLOR in
............................................................................ -

-f Equivalent to whatis.

-F or --preformat
Format only - do not display.
...................................................................

info page與 man page類似存/usr/share/info

root@xhlinux ~]# ls -al /usr/share/info
total 10804
drwxr-xr-x    2 root root 12288 Aug 16 23:38 .
drwxr-xr-x 207 root root   4096 Aug 16 23:39 ..
-rw-r--r--    1 root root 82802 May 3 2007 a2ps.info.gz
-rw-r--r--    1 root root 10441 Jan 18 2007 accounting.info.gz
-rw-r--r--    1 root root 15328 Aug 13 2006 ada-mode.gz
-rw-r--r--    1 root root 14200 Jul 26 2008 annotate.info.gz
-rw-r--r--    1 root root 178879 Jul 26 2008 as.info.gz
....................................
[root@xhlinux ~]# info info ~~~~~~~~~~~~檢視info 幫助檔案

File: info.info, Node: Help-Small-Screen, Next: Help, Up: Getting Started

1.1 Starting Info on a Small Screen
===================================

Since your terminal has a relatively small number of lines on its
screen, it is necessary to give you special advice at the beginning.

If you see the text `--All----' near the bottom right corner of the
screen, it means the entire text you are looking at fits on the screen.
If you see `--Top----' instead, it means that there is more text below
that does not fit. To move forward through the text and see another
screen full, press , the Space bar. To move back up, press the
key labeled `Backspace' or `DEL' (on some keyboards, this key might be
labeled `Delete').

Here are 40 lines of junk, so you can try and and see
what they do. At the end are instructions of what you should do next.

基本檢視時操作：空格向下翻一頁,pagedown 向下翻一頁,pageup向上翻一頁, tab在node間移動 (NODE地方通常顯示為*)
回車當游標在node 上時回車可以進入該node
b:移動游標到當前info畫面中第一個node 處
e:移動游標到當前info畫面中最後一個node處
n：前往下一個info page 處
p:前往上一個info page處
u:向上移動一層
s or (/)：在info page中搜尋
h:顯示幫助選單
?:命令一覽表
q：結束關閉info page

Search for string [at]: 按/ 搜尋at

？命令一覽
Basic Commands in Info Windows
******************************

l           Quit this help.
C-x C-c     Quit Info altogether.
h           Invoke the Info tutorial.

Selecting other nodes:
----------------------
n           Move to the "next" node of this node.
p           Move to the "previous" node of this node.
u           Move "up" from this node.
m           Pick menu item specified by name.
              Picking a menu item causes another node to be selected.
r           Follow a cross reference. Reads name of reference.
l           Move to the last node seen in this window.
TAB         Skip to next hypertext link within this node.
M-TAB       Skip to previous hypertext link within this node.
RET         Follow the hypertext link under cursor.
d           Move to the `directory' node. Equivalent to `g (DIR)'.
t           Move to the Top node. Equivalent to `g Top'.

--zz-Info: (info.info.gz)Top, 24 lines --Top------------------------------------
[root@xhlinux ~]# info info

This is line 21~~~~~~~~~~~H(顯示幫助選單)
This is line 22
This is line 23
This is line 24
This is line 25
This is line 26
This is line 27
This is line 28
This is line 29
This is line 30
This is line 31
This is line 32

--zz-Info: (info.info.gz)Help-Small-Screen, 66 lines --Top----------------------

如果想知道bash是什麼可以訪問 usr/share/doc/bash-3.0裡面有很多資訊可以參考學習
[root@xhlinux ~]# ls -al /usr/share/doc/bash-3.0
total 3776
drwxr-xr-x   11 root root   4096 Aug 16 23:19 .
drwxr-xr-x 466 root root 20480 Aug 16 23:39 ..
-rw-r--r--    1 root root 186787 Jul 17 2004 CHANGES
-rw-r--r--    1 root root   8398 Jul 17 2004 COMPAT
-rw-r--r--    1 root root 70974 Jul 22 2004 FAQ
-rw-r--r--    1 root root   7072 Feb 18 1999 INTRO
-rw-r--r--    1 root root 45847 Jul 3 2004 NEWS
-rw-r--r--    1 root root 13210 Oct 14 2003 NOTES
-rw-r--r--    1 root root   6539 Jul 27 2004 POSIX
-rw-r--r--    1 root root 41762 Oct 20 1994 article.ms
-rw-r--r--    1 root root 81474 Nov 20 2001 article.ps
-rw-r--r--    1 root root 48004 Oct 29 1994 article.txt
-rw-r--r--    1 root root 321470 Jul 12 2004 bash.0

linux關機

[root@xhlinux ~]# sync 磁碟同步,linux系統中為了加快資料讀取速度,default下某些資料不會直接寫入disk，而是先存記憶體中 ,可以手動執行SYNC 將資料寫入disk
避免不正常情況下資料未寫入disk
shutdown,reboot,halt 命令在關機前，自動進行了 SYNC 呼叫

常用的關機命令:

[root@xhlinux ~]# man shutdown 先看下如何使用
man: No such file or directory
Failed to open the message catalog man on the path NLSPATH=

Formatting page, please wait...
SHUTDOWN(8) Linux System Administrator's Manual SHUTDOWN(8)

NAME
shutdown - bring the system down

SYNOPSIS
/sbin/shutdown [-t sec] [-arkhncfF] time [warning-message]

DESCRIPTION
       shutdown brings the system down in a secure way. All logged-in users
       are notified that the system is going down, and login(1) is blocked.
       It is possible to shut the system down immediately or after a speci-
       fied delay. All processes are first notified that the system is going
       down by the signal SIGTERM. This gives programs like vi(1) the time
       to save the file being edited, mail and news processing programs a
       chance to exit cleanly, etc. shutdown does its job by signalling the
       init process, asking it to change the runlevel. Runlevel 0 is used to
       halt the system, runlevel 6 is used to reboot the system, and runlevel
       1 is used to put to system into a state where administrative tasks can
       be performed; this is the default if neither the -h or -r flag is
       given to shutdown. To see which actions are taken on halt or reboot
       see the appropriate entries for these runlevels in the file /etc/init-
       tab.

OPTIONS
-a Use /etc/shutdown.allow.

       -t sec Tell init(8) to wait sec seconds between sending processes the
              warning and the kill signal, before changing to another run-
              level.

-k Don't really shutdown; only send the warning messages to every-
body.

-r Reboot after shutdown.

-h Halt after shutdown.

       -n     [DEPRECATED] Don't call init(8) to do the shutdown but do it
              ourself. The use of this option is discouraged, and its
              results are not always what you'd expect.

-f Skip fsck on reboot.

-F Force fsck on reboot.

       -c     Cancel an already running shutdown. With this option it is of
              course not possible to give the time argument, but you can
              enter a explanatory message on the command line that will be
              sent to all users.

time When to shutdown.

warning-message
Message to send to all users.

       The time argument can have different formats. First, it can be an
       absolute time in the format hh:mm, in which hh is the hour (1 or 2
       digits) and mm is the minute of the hour (in two digits). Second, it
       can be in the format +m, in which m is the number of minutes to wait.
       The word now is an alias for +0.

       If shutdown is called with a delay, it creates the advisory file
       /etc/nologin which causes programs such as login(1) to not allow new
       user logins. Shutdown removes this file if it is stopped before it can
       signal init (i.e. it is cancelled or something goes wrong). It also
       removes it before calling init to change the runlevel.

       The -f flag means 'reboot fast'. This only creates an advisory file
       /fastboot which can be tested by the system when it comes up again.
       The boot rc file can test if this file is present, and decide not to
       run fsck(1) since the system has been shut down in the proper way.
       After that, the boot process should remove /fastboot.

       The -F flag means 'force fsck'. This only creates an advisory file
       /forcefsck which can be tested by the system when it comes up again.
       The boot rc file can test if this file is present, and decide to run
       fsck(1) with a special 'force' flag so that even properly unmounted
       filesystems get checked. After that, the boot process should remove
       /forcefsck.

       The -n flag causes shutdown not to call init, but to kill all running
       processes itself. shutdown will then turn off quota, accounting, and
       swapping and unmount all filesystems.

ACCESS CONTROL
       shutdown can be called from init(8) when the magic keys CTRL-ALT-DEL
       are pressed, by creating an appropriate entry in /etc/inittab. This
       means that everyone who has physical access to the console keyboard
       can shut the system down. To prevent this, shutdown can check to see
       if an authorized user is logged in on one of the virtual consoles. If
       shutdown is called with the -a argument (add this to the invocation of
       shutdown in /etc/inittab), it checks to see if the file /etc/shut-
       down.allow is present. It then compares the login names in that file
       with the list of people that are logged in on a virtual console (from
       /var/run/utmp). Only if one of those authorized users or root is
       logged in, it will proceed. Otherwise it will write the message

shutdown: no authorized users logged in

       to the (physical) system console. The format of /etc/shutdown.allow is
       one user name per line. Empty lines and comment lines (prefixed by a
       #) are allowed. Currently there is a limit of 32 users in this file.

Note that if /etc/shutdown.allow is not present, the -a argument is
ignored.

FILES
       /fastboot
       /etc/inittab
       /etc/init.d/halt
       /etc/init.d/reboot
       /etc/shutdown.allow

NOTES
       A lot of users forget to give the time argument and are then puzzled
       by the error message shutdown produces. The time argument is manda-
       tory; in 90 percent of all cases this argument will be the word now.

       Init can only capture CTRL-ALT-DEL and start shutdown in console mode.
       If the system is running the X window System, the X server processes
       all key strokes. Some X11 environments make it possible to capture
       CTRL-ALT-DEL, but what exactly is done with that event depends on that
       environment.

       Shutdown wasn't designed to be run setuid. /etc/shutdown.allow is not
       used to find out who is executing shutdown, it ONLY checks who is cur-
       rently logged in on (one of the) console(s).

AUTHOR
Miquel van Smoorenburg, miquels@cistron.nl

SEE ALSO
fsck(8), init(8), halt(8), poweroff(8), reboot(8)

-t sec:-t後加秒數，幾秒後關機
-k:不真關機，只發警告
-r:系統服務停掉後重啟機器
-h:系統服務停掉後關機
-n:不經過init 程式，直接shutdown關機
-f:關機並啟動後，強制略過 fsck的磁碟檢查
-F:系統重啟後，強制 FSCk 的磁碟檢查
-c:取消正在程式的 shutdown 命令

[root@xhlinux ~]# shutdown -k now 'this is shutdown test'

Broadcast message from root (pts/1) (Mon Oct 19 22:32:20 2009):

this is shutdown test
The system is going down to maintenance mode NOW!

Shutdown cancelled.
立即發出一個警告，但不關機

Shutdown cancelled.
[root@xhlinux ~]# shutdown -h +5～～～～5分鐘後關機（-h 24:00 ,-h now 馬上關機,-h now '可加警告'） 24點關機

Broadcast message from root (pts/1) (Mon Oct 19 22:32:58 2009):

The system is going DOWN for system halt in 5 minutes!

[root@xhlinux ~]# shutdown -r now 立即重新啟動 (-r +30 'ssssss' 30分鐘後重新啟動加警告)

Broadcast message from root (pts/1) (Mon Oct 19 22:34:28 2009):

The system is going down for reboot NOW!
[root@xhlinux ~]#

另外這些後面都可以跟警告

重啟
reboot,halt,poweroff,3個命令基本一樣

reboot與 shutdown -r now一樣

[root@xhlinux ~]# halt

Broadcast message from root (pts/1) (Mon Oct 19 22:37:54 2009):

The system is going down for system halt NOW!
[root@xhlinux ~]#

　功能說明：關閉系統。

　　語　　法：halt [-dfinpw]

　　補充說明：halt會先檢測系統的runlevel。若runlevel為0或6，則關閉系統，否則即呼叫shutdown來關閉系統。

　　參　　數：
　　-d 　不要在wtmp中記錄。
　　-f 　不論目前的runlevel為何，不呼叫shutdown即強制關閉系統。
　　-i 　在halt之前，關閉全部的網路介面。
　　-n 　halt前，不用先執行sync。
　　-p 　halt之後，執行poweroff。
　　-w 　僅在wtmp中記錄，而不實際結束系統。
具體使用可以查 man halt,man poweroff，建議reboot前執行sync, sycn;reboot

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