system.html

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><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>tset -r</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>Terminal type is xterm-xfree86.
 Kill is control-U (^U).
 Interrupt is control-C (^C).</TT
>
 	      </PRE
></TD
></TR
></TABLE
>
	    </P
></DD
><DT
><A
NAME="SETSERIALREF"
></A
><B
CLASS="COMMAND"
>setserial</B
></DT
><DD
><P
>Set or display serial port parameters. This command must be
	      run by <I
CLASS="FIRSTTERM"
>root</I
> and is usually found in a
	      system setup script.</P
><P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;# From /etc/pcmcia/serial script:
   2&nbsp;
   3&nbsp;IRQ=`setserial /dev/$DEVICE | sed -e 's/.*IRQ: //'`
   4&nbsp;setserial /dev/$DEVICE irq 0 ; setserial /dev/$DEVICE irq $IRQ</PRE
></TD
></TR
></TABLE
></P
></DD
><DT
><A
NAME="GETTYREF"
></A
><B
CLASS="COMMAND"
>getty</B
>, <A
NAME="AGETTYREF"
></A
><B
CLASS="COMMAND"
>agetty</B
></DT
><DD
><P
>The initialization process for a terminal uses
	      <B
CLASS="COMMAND"
>getty</B
> or <B
CLASS="COMMAND"
>agetty</B
>
	      to set it up for login by a user. These commands are not
	      used within user shell scripts. Their scripting counterpart
	      is <B
CLASS="COMMAND"
>stty</B
>.</P
></DD
><DT
><A
NAME="MESGREF"
></A
><B
CLASS="COMMAND"
>mesg</B
></DT
><DD
><P
>Enables or disables write access to the current user's
	      terminal.  Disabling access would prevent another user
	      on the network to <A
HREF="communications.html#WRITEREF"
>write</A
>
	      to the terminal.</P
><DIV
CLASS="TIP"
><TABLE
CLASS="TIP"
WIDTH="90%"
BORDER="0"
><TR
><TD
WIDTH="25"
ALIGN="CENTER"
VALIGN="TOP"
><IMG
SRC="common/tip.png"
HSPACE="5"
ALT="Tip"></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><P
>It can be quite annoying to have a message
	      about ordering pizza suddenly appear in the middle of
	      the text file you are editing. On a multi-user network,
	      you might therefore wish to disable write access to your
	      terminal when you need to avoid interruptions.</P
></TD
></TR
></TABLE
></DIV
></DD
><DT
><A
NAME="WALLREF"
></A
><B
CLASS="COMMAND"
>wall</B
></DT
><DD
><P
>This is an acronym for <SPAN
CLASS="QUOTE"
>"<A
HREF="communications.html#WRITEREF"
>write</A
> all,"</SPAN
> i.e., sending
	      a message to all users at every terminal logged into the
	      network. It is primarily a system administrator's tool,
	      useful, for example, when warning everyone that the
	      system will shortly go down due to a problem (see <A
HREF="here-docs.html#EX70"
>Example 18-1</A
>).</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </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
	      that terminal.</P
></TD
></TR
></TABLE
></DIV
></DD
></DL
></DIV
><DIV
CLASS="VARIABLELIST"
><P
><B
><A
NAME="STATISTICSSYS1"
></A
>Information and Statistics</B
></P
><DL
><DT
><A
NAME="UNAMEREF"
></A
><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 15-5</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</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>Linux</TT
>
 
 <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>uname -s</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>Linux</TT
>
 
 
 <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>uname -a</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>Linux iron.bozo 2.6.15-1.2054_FC5 #1 Tue Mar 14 15:48:33 EST 2006
 i686 i686 i386 GNU/Linux</TT
></PRE
></TD
></TR
></TABLE
></DD
><DT
><A
NAME="ARCHREF"
></A
><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
><A
NAME="LASTCOMMREF"
></A
><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
><A
NAME="LSOFREF"
></A
><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
><P
>The <B
CLASS="COMMAND"
>lsof</B
> command is a useful,
	      if complex administrative tool. If you are unable to
	      dismount a filesystem and get an error message that it is
	      still in use, then running <I
CLASS="FIRSTTERM"
>lsof</I
> helps
	      determine which files are still open on that filesystem. The
	      <TT
CLASS="OPTION"
>-i</TT
> option lists open network socket files,
	      and this can help trace intrusion or hack attempts.</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>lsof -an -i tcp</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>COMMAND  PID USER  FD  TYPE DEVICE SIZE NODE NAME
 firefox 2330 bozo  32u IPv4   9956       TCP 66.0.118.137:57596-&#62;67.112.7.104:http ...
 firefox 2330 bozo  38u IPv4  10535       TCP 66.0.118.137:57708-&#62;216.79.48.24:http ...</TT
>
 	      </PRE
></TD
></TR
></TABLE
>
	    </P
></DD
><DT
><A
NAME="STRACEREF"
></A
><B
CLASS="COMMAND"
>strace</B
></DT
><DD
><P
><B
CLASS="COMMAND"
>S</B
>ystem <B
CLASS="COMMAND"
>trace</B
>:
	      diagnostic and debugging tool for tracing <I
CLASS="FIRSTTERM"
>system
	      calls</I
> and signals. This command and
	      <B
CLASS="COMMAND"
>ltrace</B
>, following, are useful for
	      diagnosing why a given program or package fails to
	      run . . . perhaps due to missing libraries or related
	      causes.</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="LTRACEREF"
></A
><B
CLASS="COMMAND"
>ltrace</B
></DT
><DD
><P
><B
CLASS="COMMAND"
>L</B
>ibrary <B
CLASS="COMMAND"
>trace</B
>:
	      diagnostic and debugging tool that traces <I
CLASS="FIRSTTERM"
>library calls</I
>
	      invoked by a given command.</P
><P
>	    <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>ltrace df</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>__libc_start_main(0x804a910, 1, 0xbfb589a4, 0x804fb70, 0x804fb68 &#60;unfinished ...&#62;:
 setlocale(6, "")                                 = "en_US.UTF-8"
bindtextdomain("coreutils", "/usr/share/locale") = "/usr/share/locale"
textdomain("coreutils")                          = "coreutils"
__cxa_atexit(0x804b650, 0, 0, 0x8052bf0, 0xbfb58908) = 0
getenv("DF_BLOCK_SIZE")                          = NULL

 ...</TT
>
 	    </PRE
></TD
></TR
></TABLE
>
	    </P
></DD
><DT
><A
NAME="NMAPREF"
></A
><B
CLASS="COMMAND"
>nmap</B
></DT
><DD
><P
><B
CLASS="COMMAND"
>N</B
>etwork <B
CLASS="COMMAND"
>map</B
>per
	      and port scanner. This command scans a server to
	      locate open ports and the services associated with those
	      ports. It can also report information about packet filters and
	      firewalls. This 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
><A
NAME="NCREF"
></A
><B
CLASS="COMMAND"
>nc</B
></DT
><DD
><P
>The <B
CLASS="COMMAND"
>nc</B
> (<I
CLASS="FIRSTTERM"
>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 16-5. Checking a remote server for
              <I
CLASS="FIRSTTERM"
>identd</I
></B
></P
><TABLE
BORDER="0"