system.html

一本完整的描述Unix Shell 编程的工具书的所有范例

></TABLE
></DIV
></DD
><DT
><A
NAME="WALLREF"
></A
><B
CLASS="COMMAND"
>wall</B
></DT
><DD
><P
>This is an acronym for <SPAN
CLASS="QUOTE"
>"<A
HREF="communications.html#WRITEREF"
>write</A
> all"</SPAN
>, i.e., sending
	      a message to all users at every terminal logged into the
	      network. It is primarily a system administrator's tool,
	      useful, for example, when warning everyone that the
	      system will shortly go down due to a problem (see <A
HREF="here-docs.html#EX70"
>Example 17-1</A
>).</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>wall System going down for maintenance in 5 minutes!</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>Broadcast message from bozo (pts/1) Sun Jul  8 13:53:27 2001...

 System going down for maintenance in 5 minutes!</TT
>
 	      </PRE
></TD
></TR
></TABLE
>
	    </P
><DIV
CLASS="NOTE"
><TABLE
CLASS="NOTE"
WIDTH="90%"
BORDER="0"
><TR
><TD
WIDTH="25"
ALIGN="CENTER"
VALIGN="TOP"
><IMG
SRC="common/note.png"
HSPACE="5"
ALT="Note"></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>If write access to a particular terminal has been
	      disabled with <B
CLASS="COMMAND"
>mesg</B
>, then
	      <B
CLASS="COMMAND"
>wall</B
> cannot send a message to
	      it.</P
></TD
></TR
></TABLE
></DIV
></DD
></DL
></DIV
><DIV
CLASS="VARIABLELIST"
><P
><B
><A
NAME="STATISTICSSYS1"
></A
>Information and Statistics</B
></P
><DL
><DT
><B
CLASS="COMMAND"
>uname</B
></DT
><DD
><P
>Output system specifications (OS, kernel version,
	      etc.) to <TT
CLASS="FILENAME"
>stdout</TT
>.  Invoked with the
	      <TT
CLASS="OPTION"
>-a</TT
> option, gives verbose system info
	      (see <A
HREF="moreadv.html#EX41"
>Example 12-5</A
>). The <TT
CLASS="OPTION"
>-s</TT
>
	      option shows only the OS type.</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>uname -a</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>Linux localhost.localdomain 2.2.15-2.5.0 #1 Sat Feb 5 00:13:43 EST 2000 i686 unknown</TT
>
 
 <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>uname -s</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>Linux</TT
></PRE
></TD
></TR
></TABLE
></DD
><DT
><B
CLASS="COMMAND"
>arch</B
></DT
><DD
><P
>Show system architecture.
	      Equivalent to <B
CLASS="COMMAND"
>uname -m</B
>. See <A
HREF="testbranch.html#CASECMD"
>Example 10-26</A
>.</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>arch</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>i686</TT
>
 
 <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>uname -m</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>i686</TT
></PRE
></TD
></TR
></TABLE
></DD
><DT
><B
CLASS="COMMAND"
>lastcomm</B
></DT
><DD
><P
>Gives information about previous commands, as stored
	      in the <TT
CLASS="FILENAME"
>/var/account/pacct</TT
> file. Command
	      name and user name can be specified by options. This is
	      one of the GNU accounting utilities.</P
></DD
><DT
><A
NAME="LASTLOGREF"
></A
><B
CLASS="COMMAND"
>lastlog</B
></DT
><DD
><P
>List the last login time of all system users. This
	      references the <TT
CLASS="FILENAME"
>/var/log/lastlog</TT
>
	      file.</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>lastlog</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>root          tty1                      Fri Dec  7 18:43:21 -0700 2001
 bin                                     **Never logged in**
 daemon                                  **Never logged in**
 ...
 bozo          tty1                      Sat Dec  8 21:14:29 -0700 2001</TT
>
 
 
 
 <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>lastlog | grep root</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>root          tty1                      Fri Dec  7 18:43:21 -0700 2001</TT
>
 	      </PRE
></TD
></TR
></TABLE
>
	      </P
><DIV
CLASS="CAUTION"
><TABLE
CLASS="CAUTION"
WIDTH="90%"
BORDER="0"
><TR
><TD
WIDTH="25"
ALIGN="CENTER"
VALIGN="TOP"
><IMG
SRC="common/caution.png"
HSPACE="5"
ALT="Caution"></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>This command will fail if the user invoking
		it does not have read permission for the
		<TT
CLASS="FILENAME"
>/var/log/lastlog</TT
> file.</P
></TD
></TR
></TABLE
></DIV
></DD
><DT
><B
CLASS="COMMAND"
>lsof</B
></DT
><DD
><P
>List open files. This command outputs a detailed
	      table of all currently open files and gives information
	      about their owner, size, the processes associated with
	      them, and more. Of course, <B
CLASS="COMMAND"
>lsof</B
> may
	      be piped to <A
HREF="textproc.html#GREPREF"
>grep</A
> and/or
	      <A
HREF="awk.html#AWKREF"
>awk</A
> to parse and analyze
	      its results.</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>lsof</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>COMMAND    PID    USER   FD   TYPE     DEVICE    SIZE     NODE NAME
 init         1    root  mem    REG        3,5   30748    30303 /sbin/init
 init         1    root  mem    REG        3,5   73120     8069 /lib/ld-2.1.3.so
 init         1    root  mem    REG        3,5  931668     8075 /lib/libc-2.1.3.so
 cardmgr    213    root  mem    REG        3,5   36956    30357 /sbin/cardmgr
 ...</TT
>
 	      </PRE
></TD
></TR
></TABLE
>
	    </P
></DD
><DT
><B
CLASS="COMMAND"
>strace</B
></DT
><DD
><P
>Diagnostic and debugging tool for tracing system
	      calls and signals. The simplest way of invoking it is
	      <B
CLASS="COMMAND"
>strace COMMAND</B
>.</P
><P
>	    <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>strace df</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>execve("/bin/df", ["df"], [/* 45 vars */]) = 0
 uname({sys="Linux", node="bozo.localdomain", ...}) = 0
 brk(0)                                  = 0x804f5e4
 ...</TT
>
 	    </PRE
></TD
></TR
></TABLE
>
	    </P
><P
>This is the Linux equivalent of
	      the Solaris <B
CLASS="COMMAND"
>truss</B
> command.</P
></DD
><DT
><A
NAME="NMAPREF"
></A
><B
CLASS="COMMAND"
>nmap</B
></DT
><DD
><P
>Network port scanner. This command scans a server to
	      locate open ports and the services associated with those
	      ports. It is an important security tool for locking down
	      a network against hacking attempts.</P
><P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;
   3&nbsp;SERVER=$HOST                           # localhost.localdomain (127.0.0.1).
   4&nbsp;PORT_NUMBER=25                         # SMTP port.
   5&nbsp;
   6&nbsp;nmap $SERVER | grep -w "$PORT_NUMBER"  # Is that particular port open?
   7&nbsp;#              grep -w matches whole words only,
   8&nbsp;#+             so this wouldn't match port 1025, for example.
   9&nbsp;
  10&nbsp;exit 0
  11&nbsp;
  12&nbsp;# 25/tcp     open        smtp</PRE
></TD
></TR
></TABLE
></P
></DD
><DT
><B
CLASS="COMMAND"
>nc</B
></DT
><DD
><P
>The <B
CLASS="COMMAND"
>nc</B
> (<I
CLASS="EMPHASIS"
>netcat</I
>)
	      utility is a complete toolkit for connecting to and
	      listening to TCP and UDP ports. It is useful as a diagnostic
	      and testing tool and as a component in simple script-based HTTP
	      clients and servers.</P
><P
>	    <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>nc localhost.localdomain 25</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>220 localhost.localdomain ESMTP Sendmail 8.13.1/8.13.1; Thu, 31 Mar 2005 15:41:35 -0700</TT
></PRE
></TD
></TR
></TABLE
>
	    </P
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="ISCAN"
></A
><P
><B
>Example 13-5. Checking a remote server for <I
CLASS="EMPHASIS"
>identd</I
></B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#! /bin/sh
   2&nbsp;## Duplicate DaveG's ident-scan thingie using netcat. Oooh, he'll be p*ssed.
   3&nbsp;## Args: target port [port port port ...]
   4&nbsp;## Hose stdout _and_ stderr together.
   5&nbsp;##
   6&nbsp;##  Advantages: runs slower than ident-scan, giving remote inetd less cause
   7&nbsp;##+ for alarm, and only hits the few known daemon ports you specify.
   8&nbsp;##  Disadvantages: requires numeric-only port args, the output sleazitude,
   9&nbsp;##+ and won't work for r-services when coming from high source ports.
  10&nbsp;# Script author: Hobbit &#60;[e-mail]&#62;
  11&nbsp;# Used in ABS Guide with permission.
  12&nbsp;
  13&nbsp;# ---------------------------------------------------
  14&nbsp;E_BADARGS=65       # Need at least two args.
  15&nbsp;TWO_WINKS=2        # How long to sleep.
  16&nbsp;THREE_WINKS=3
  17&nbsp;IDPORT=113         # Authentication "tap ident" port.
  18&nbsp;RAND1=999
  19&nbsp;RAND2=31337
  20&nbsp;TIMEOUT0=9
  21&nbsp;TIMEOUT1=8
  22&nbsp;TIMEOUT2=4
  23&nbsp;# ---------------------------------------------------
  24&nbsp;
  25&nbsp;case "${2}" in
  26&nbsp;  "" ) echo "Need HOST and at least one PORT." ; exit $E_BADARGS ;;
  27&nbsp;esac
  28&nbsp;
  29&nbsp;# Ping 'em once and see if they *are* running identd.
  30&nbsp;nc -z -w $TIMEOUT0 "$1" $IDPORT || { echo "Oops, $1 isn't running identd." ; exit 0 ; }
  31&nbsp;#  -z scans for listening daemons.
  32&nbsp;#     -w $TIMEOUT = How long to try to connect.
  33&nbsp;
  34&nbsp;# Generate a randomish base port.
  35&nbsp;RP=`expr $$ % $RAND1 + $RAND2`
  36&nbsp;
  37&nbsp;TRG="$1"
  38&nbsp;shift
  39&nbsp;
  40&nbsp;while test "$1" ; do
  41&nbsp;  nc -v -w $TIMEOUT1 -p ${RP} "$TRG" ${1} &#60; /dev/null &#62; /dev/null &#38;
  42&nbsp;  PROC=$!
  43&nbsp;  sleep $THREE_WINKS
  44&nbsp;  echo "${1},${RP}" | nc -w $TIMEOUT2 -r "$TRG" $IDPORT 2&#62;&#38;1
  45&nbsp;  sleep $TWO_WINKS
  46&nbsp;
  47&nbsp;# Does this look like a lamer script or what . . . ?
  48&nbsp;# ABS Guide author comments: "It ain't really all that bad,
  49&nbsp;#+                            rather clever, actually."
  50&nbsp;
  51&nbsp;  kill -HUP $PROC
  52&nbsp;  RP=`expr ${RP} + 1`
  53&nbsp;  shift
  54&nbsp;done
  55&nbsp;
  56&nbsp;exit $?
  57&nbsp;
  58&nbsp;#  Notes:
  59&nbsp;#  -----
  60&nbsp;
  61&nbsp;#  Try commenting out line 30 and running this script
  62&nbsp;#+ with "localhost.localdomain 25" as arguments.
  63&nbsp;
  64&nbsp;#  For more of Hobbit's 'nc' example scripts,
  65&nbsp;#+ look in the documentation:
  66&nbsp;#+ the /usr/share/doc/nc-X.XX/scripts directory.</PRE
></TD
></TR
></TABLE
><HR></DIV
><P
>	      And, of course, there's Dr. Andrew Tridgell's notorious
	      one-line script in the BitKeeper Affair:
	        <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;echo clone | nc thunk.org 5000 &#62; e2fsprogs.dat</PRE
></TD
></TR
></TABLE
>
	    </P
></DD
><DT
><A
NAME="FREEREF"
></A
><B
CLASS="COMMAND"
>free</B
></DT
><DD
><P
>Shows memory and cache usage in tabular form. The
	      output of this command lends itself to parsing, using
	      <A
HREF="textproc.html#GREPREF"
>grep</A
>, <A
HREF="awk.html#AWKREF"
>awk</A
> or <B
CLASS="COMMAND"
>Perl</B
>. The
	      <B
CLASS="COMMAND"
>procinfo</B
> command shows all the
	      information that <B
CLASS="COMMAND"
>free</B
> does, and much
	      more.</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><B
CLASS="COMMAND"
>free</B
>
 <TT
CLASS="COMPUTEROUTPUT"
>                total       used       free     shared    buffers     cached
   Mem:         30504      28624       1880      15820       1608       16376
   -/+ buffers/cache:      10640      19864
   Swap:        68540       3128      65412</TT
></PRE
></TD
></TR
></TABLE
><P
>To show unused RAM memory:</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><B
CLASS="COMMAND"
>free | grep Mem | awk '{ print $4 }'</B
>
 <TT
CLASS="COMPUTEROUTPUT"
>1880</TT
></PRE
></TD
></TR
></TABLE
></DD
><DT
><A
NAME="PROCINFOREF"
></A
><B
CLASS="COMMAND"
>procinfo</B
></DT
><DD
><P
>Extract and list information and statistics from the
	      <A
HREF="devproc.html#DEVPROCREF"
><TT
CLASS="FILENAME"
>/proc</TT
>
	      pseudo-filesystem</A
>. This gives a very extensive and
	      detailed listing.</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>procinfo | grep Bootup</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>Bootup: Wed Mar 21 15:15:50 2001    Load average: 0.04 0.21 0.34 3/47 6829</TT
></PRE
></TD
></TR
></TABLE
></DD
><DT
><A
NAME="LSDEVREF"
></A
><B
CLASS="COMMAND"
>lsdev</B
></DT
><DD
><P
>List devices, that is, show installed hardware.</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>lsdev</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>Device            DMA   IRQ  I/O Ports
 ------------------------------------------------
 cascade             4     2 
 dma                          0080-008f
 dma1                         0000-001f
 dma2                         00c0-00df
 fpu                          00f0-00ff
 ide0                     14  01f0-01f7 03f6-03f6
 ...</TT
>
 	      </PRE
></TD
></TR
></TABLE
>
	      </P
></DD
><DT
><A
NAME="DUREF"
></A
><B
CLASS="COMMAND"
>du</B
></DT
><DD
><P
>Show (disk) file usage, recursively. Defaults to current
	      working directory, unless otherwise specified.</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT