system.html

Shall高级编程

	      <B
CLASS="COMMAND"
>domainname</B
>,
	      <B
CLASS="COMMAND"
>dnsdomainname</B
>,
	      <B
CLASS="COMMAND"
>nisdomainname</B
>, and
	      <B
CLASS="COMMAND"
>ypdomainname</B
> commands. Use these to
	      display or set the system DNS or NIS/YP domain name. Various
	      options to <B
CLASS="COMMAND"
>hostname</B
> also perform these
	      functions.</P
></DD
><DT
><A
NAME="HOSTIDREF"
></A
><B
CLASS="COMMAND"
>hostid</B
></DT
><DD
><P
>Echo a 32-bit hexadecimal numerical identifier for the
	      host machine.</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>hostid</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>7f0100</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
>This command allegedly fetches a <SPAN
CLASS="QUOTE"
>"unique"</SPAN
>
	      serial number for a particular system. Certain
	      product registration procedures use this number
	      to brand a particular user license. Unfortunately,
	      <B
CLASS="COMMAND"
>hostid</B
> only returns the machine
	      network address in hexadecimal, with pairs of bytes
	      transposed.</P
><P
>The network address of a typical non-networked Linux
	      machine, is found in <TT
CLASS="FILENAME"
>/etc/hosts</TT
>.</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>cat /etc/hosts</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>127.0.0.1               localhost.localdomain localhost</TT
></PRE
></TD
></TR
></TABLE
>
	    </P
><P
>As it happens, transposing the bytes of
	      <TT
CLASS="USERINPUT"
><B
>127.0.0.1</B
></TT
>, we get
	      <TT
CLASS="USERINPUT"
><B
>0.127.1.0</B
></TT
>, which translates in
	      hex to <TT
CLASS="USERINPUT"
><B
>007f0100</B
></TT
>, the exact equivalent
	      of what <B
CLASS="COMMAND"
>hostid</B
> returns, above. There
	      exist only a few million other Linux machines with this
	      identical <I
CLASS="FIRSTTERM"
>hostid</I
>.</P
></TD
></TR
></TABLE
></DIV
></DD
><DT
><A
NAME="SARREF"
></A
><B
CLASS="COMMAND"
>sar</B
></DT
><DD
><P
>Invoking <B
CLASS="COMMAND"
>sar</B
> (System Activity Reporter)
	      gives a very detailed rundown on system statistics. The
	      Santa Cruz Operation (<SPAN
CLASS="QUOTE"
>"Old"</SPAN
> SCO) released
	      <B
CLASS="COMMAND"
>sar</B
> as Open Source in June, 1999.</P
><P
>This command is not part of the base Linux distribution,
	      but may be obtained as part of the<A
HREF="http://perso.wanadoo.fr/sebastien.godard/"
TARGET="_top"
>	      sysstat utilities</A
> package, written by <A
HREF="mailto:[e-mail]"
TARGET="_top"
>Sebastien
	      Godard</A
>.</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>sar</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>Linux 2.4.9 (brooks.seringas.fr) 	09/26/03

10:30:00          CPU     %user     %nice   %system   %iowait     %idle
10:40:00          all      2.21     10.90     65.48      0.00     21.41
10:50:00          all      3.36      0.00     72.36      0.00     24.28
11:00:00          all      1.12      0.00     80.77      0.00     18.11
Average:          all      2.23      3.63     72.87      0.00     21.27

14:32:30          LINUX RESTART

15:00:00          CPU     %user     %nice   %system   %iowait     %idle
15:10:00          all      8.59      2.40     17.47      0.00     71.54
15:20:00          all      4.07      1.00     11.95      0.00     82.98
15:30:00          all      0.79      2.94      7.56      0.00     88.71
Average:          all      6.33      1.70     14.71      0.00     77.26</TT
>
            </PRE
></TD
></TR
></TABLE
></DD
><DT
><A
NAME="READELFREF"
></A
><B
CLASS="COMMAND"
>readelf</B
></DT
><DD
><P
>Show information and statistics about a designated
	      <I
CLASS="FIRSTTERM"
>elf</I
> binary. This is part of the
	      <I
CLASS="FIRSTTERM"
>binutils</I
> package.</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>readelf -h /bin/bash</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>ELF Header:
   Magic:   7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00 
   Class:                             ELF32
   Data:                              2's complement, little endian
   Version:                           1 (current)
   OS/ABI:                            UNIX - System V
   ABI Version:                       0
   Type:                              EXEC (Executable file)
   . . .</TT
></PRE
></TD
></TR
></TABLE
></DD
><DT
><A
NAME="SIZEREF"
></A
><B
CLASS="COMMAND"
>size</B
></DT
><DD
><P
>The <B
CLASS="COMMAND"
>size [/path/to/binary]</B
> command
	      gives the segment sizes of a binary executable or archive file.
	      This is mainly of use to programmers.</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>size /bin/bash</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>   text    data     bss     dec     hex filename
  495971   22496   17392  535859   82d33 /bin/bash</TT
>
 	      </PRE
></TD
></TR
></TABLE
>
	    </P
></DD
></DL
></DIV
><DIV
CLASS="VARIABLELIST"
><P
><B
><A
NAME="SYSLOG1"
></A
>System Logs</B
></P
><DL
><DT
><A
NAME="LOGGERREF"
></A
><B
CLASS="COMMAND"
>logger</B
></DT
><DD
><P
>Appends a user-generated message to the system log
	      (<TT
CLASS="FILENAME"
>/var/log/messages</TT
>). You do not have
	      to be <I
CLASS="FIRSTTERM"
>root</I
> to invoke
	      <B
CLASS="COMMAND"
>logger</B
>.</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;logger Experiencing instability in network connection at 23:10, 05/21.
   2&nbsp;# Now, do a 'tail /var/log/messages'.</PRE
></TD
></TR
></TABLE
></P
><P
>By embedding a <B
CLASS="COMMAND"
>logger</B
> command in a script,
	      it is possible to write debugging information to
	      <TT
CLASS="FILENAME"
>/var/log/messages</TT
>.</P
><P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;logger -t $0 -i Logging at line "$LINENO".
   2&nbsp;# The "-t" option specifies the tag for the logger entry.
   3&nbsp;# The "-i" option records the process ID.
   4&nbsp;
   5&nbsp;# tail /var/log/message
   6&nbsp;# ...
   7&nbsp;# Jul  7 20:48:58 localhost ./test.sh[1712]: Logging at line 3.</PRE
></TD
></TR
></TABLE
>
            </P
></DD
><DT
><A
NAME="LOGROTATEREF"
></A
><B
CLASS="COMMAND"
>logrotate</B
></DT
><DD
><P
>This utility manages the system log files, rotating,
	      compressing, deleting, and/or e-mailing them, as appropriate.
	      This keeps the <TT
CLASS="FILENAME"
>/var/log</TT
>
	      from getting cluttered with old log files.
	      Usually <A
HREF="system.html#CRONREF"
>cron</A
> runs
	      <B
CLASS="COMMAND"
>logrotate</B
> on a daily basis.</P
><P
>Adding an appropriate entry to
	       <TT
CLASS="FILENAME"
>/etc/logrotate.conf</TT
> makes it possible
	       to manage personal log files, as well as system-wide
	       ones.</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
>Stefano Falsetto has created <A
HREF="http://www.gnu.org/software/rottlog/"
TARGET="_top"
>rottlog</A
>,
	     which he considers to be an improved version of
	     <B
CLASS="COMMAND"
>logrotate</B
>.</P
></TD
></TR
></TABLE
></DIV
></DD
></DL
></DIV
><DIV
CLASS="VARIABLELIST"
><P
><B
><A
NAME="JOBCONTROLSYS1"
></A
>Job Control</B
></P
><DL
><DT
><A
NAME="PPSSREF"
></A
><B
CLASS="COMMAND"
>ps</B
></DT
><DD
><P
><TT
CLASS="REPLACEABLE"
><I
>P</I
></TT
>rocess
	      <TT
CLASS="REPLACEABLE"
><I
>S</I
></TT
>tatistics: lists currently
	      executing processes by owner and PID (process ID). This
	      is usually invoked with <TT
CLASS="OPTION"
>ax</TT
> or
	      <TT
CLASS="OPTION"
>aux</TT
> options,
	      and may be piped to <A
HREF="textproc.html#GREPREF"
>grep</A
>
	      or <A
HREF="sedawk.html#SEDREF"
>sed</A
> to search for a
	      specific process (see <A
HREF="internal.html#EX44"
>Example 14-13</A
> and <A
HREF="procref1.html#PIDID"
>Example 27-2</A
>).</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
> ps ax | grep sendmail</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>295 ?	   S	  0:00 sendmail: accepting connections on port 25</TT
></PRE
></TD
></TR
></TABLE
><P
>To display system processes in graphical <SPAN
CLASS="QUOTE"
>"tree"</SPAN
>
	      format: <B
CLASS="COMMAND"
>ps afjx</B
> or
	      <B
CLASS="COMMAND"
>ps ax --forest</B
>.</P
></DD
><DT
><A
NAME="PGREPREF"
></A
><B
CLASS="COMMAND"
>pgrep</B
>, <A
NAME="PKILLREF"
></A
><B
CLASS="COMMAND"
>pkill</B
></DT
><DD
><P
>Combining the <B
CLASS="COMMAND"
>ps</B
> command
	      with <A
HREF="textproc.html#GREPREF"
>grep</A
> or
	      <A
HREF="internal.html#KILLREF"
>kill</A
>.</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>ps a | grep mingetty</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>2212 tty2     Ss+    0:00 /sbin/mingetty tty2
 2213 tty3     Ss+    0:00 /sbin/mingetty tty3
 2214 tty4     Ss+    0:00 /sbin/mingetty tty4
 2215 tty5     Ss+    0:00 /sbin/mingetty tty5
 2216 tty6     Ss+    0:00 /sbin/mingetty tty6
 4849 pts/2    S+     0:00 grep mingetty</TT
>
 
 
 <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>pgrep mingetty</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>2212 mingetty
 2213 mingetty
 2214 mingetty
 2215 mingetty
 2216 mingetty</TT
>
 	      </PRE
></TD
></TR
></TABLE
>
	    </P
><P
>Compare the action of <B
CLASS="COMMAND"
>pkill</B
> with <A
HREF="internal.html#KILLALLREF"
>killall</A
>.</P
></DD
><DT
><A
NAME="PSTREEREF"
></A
><B
CLASS="COMMAND"
>pstree</B
></DT
><DD
><P
>Lists currently executing processes in
	      <SPAN
CLASS="QUOTE"
>"tree"</SPAN
> format. The <TT
CLASS="OPTION"
>-p</TT
> option
	      shows the PIDs, as well as the process names.</P
></DD
><DT
><A
NAME="TOPREF"
></A
><B
CLASS="COMMAND"
>top</B
></DT
><DD
><P
>Continuously updated display of most cpu-intensive
	      processes. The <TT
CLASS="OPTION"
>-b</TT
> option displays in text
	      mode, so that the output may be parsed or accessed from
	      a script.</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>top -b</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>  8:30pm  up 3 min,  3 users,  load average: 0.49, 0.32, 0.13
 45 processes: 44 sleeping, 1 running, 0 zombie, 0 stopped
 CPU states: 13.6% user,  7.3% system,  0.0% nice, 78.9% idle
 Mem:    78396K av,   65468K used,   12928K free,       0K shrd,    2352K buff
 Swap:  157208K av,       0K used,  157208K free                   37244K cached

   PID USER     PRI  NI  SIZE  RSS SHARE STAT %CPU %MEM   TIME COMMAND
   848 bozo      17   0   996  996   800 R     5.6  1.2   0:00 top
     1 root       8   0   512  512   444 S     0.0  0.6   0:04 init
     2 root       9   0     0    0     0 SW    0.0  0.0   0:00 keventd
   ...</TT
>  
 	      </PRE
></TD
></TR
></TABLE
>
	    </P
></DD
><DT
><A
NAME="NICEREF"
></A
><B
CLASS="COMMAND"
>nice</B
></DT
><DD
><P
><A
NAME="NICE2REF"
></A
></P
><P
>Run a background job with an altered
	      priority. Priorities run from 19 (lowest) to -20
	      (highest). Only <I
CLASS="FIRSTTERM"
>root</I
> may set the
	      negative (higher) priorities. Related commands are
	      <B
CLASS="COMMAND"
>renice</B
> and <B
CLASS="COMMAND"
>snice</B
>,
	      which change the priority of a running process or
	      processes, and <B
CLASS="COMMAND"
>skill</B
>, which sends a
	      <A
HREF="internal.html#KILLREF"
>kill</A
> signal to a process
	      or processes.</P
></DD
><DT
><A
NAME="NOHUPREF"
></A
><B
CLASS="COMMAND"
>nohup</B
></DT
><DD
><P
>Keeps a command running even after user logs off.
	      The command will run as a foreground process unless followed
	      by <SPAN
CLASS="TOKEN"
>&#38;</SPAN
>.  If you use <B
CLASS="COMMAND"
>nohup</B
>
	      within a script, consider coupling it with a <A
HREF="internal.html#WAITREF"
>wait</A
> to avoid creating an
	      <I
CLASS="FIRSTTERM"
>orphan</I
> or
	      <A
HREF="internal.html#ZOMBIEREF"
>zombie</A
> process.</P
></DD
><DT
><A
NAME="PIDOFREF"
></A
><B
CLASS="COMMAND"
>pidof</B
></DT
><DD
><P
>Identifies <I