system.html

一本完整的描述Unix Shell 编程的工具书的所有范例

   6 # ...
   7&nbsp;# Jul  7 20:48:58 localhost ./test.sh[1712]: Logging at line 3.</PRE
></TD
></TR
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>
            </P
></DD
><DT
><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
><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
> 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 11-12</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
><B
CLASS="COMMAND"
>pgrep</B
>, <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
></DD
><DT
><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
><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
><B
CLASS="COMMAND"
>nice</B
></DT
><DD
><P
>Run a background job with an altered
	      priority. Priorities run from 19 (lowest) to -20
	      (highest). Only <I
CLASS="EMPHASIS"
>root</I
> may set the
	      negative (higher) priorities. Related commands are
	      <B
CLASS="COMMAND"
>renice</B
>, <B
CLASS="COMMAND"
>snice</B
>,
	      and <B
CLASS="COMMAND"
>skill</B
>.</P
></DD
><DT
><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 orphan
	      or zombie process.</P
></DD
><DT
><A
NAME="PIDOFREF"
></A
><B
CLASS="COMMAND"
>pidof</B
></DT
><DD
><P
>Identifies <I
CLASS="EMPHASIS"
>process ID (PID)</I
> of a
	    running job. Since job control commands, such as <A
HREF="internal.html#KILLREF"
>kill</A
> and <B
CLASS="COMMAND"
>renice</B
>
	    act on the <I
CLASS="EMPHASIS"
>PID</I
> of a process (not
	    its name), it is sometimes necessary to identify that
	    <I
CLASS="EMPHASIS"
>PID</I
>.  The <B
CLASS="COMMAND"
>pidof</B
>
	    command is the approximate counterpart to the <A
HREF="variables2.html#PPIDREF"
>$PPID</A
> internal variable.</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>pidof xclock</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>880</TT
>
 	      </PRE
></TD
></TR
></TABLE
>
	    </P
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="KILLPROCESS"
></A
><P
><B
>Example 13-6. <B
CLASS="COMMAND"
>pidof</B
> helps kill a process</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;# kill-process.sh
   3&nbsp;
   4&nbsp;NOPROCESS=2
   5&nbsp;
   6&nbsp;process=xxxyyyzzz  # Use nonexistent process.
   7&nbsp;# For demo purposes only...
   8&nbsp;# ... don't want to actually kill any actual process with this script.
   9&nbsp;#
  10&nbsp;# If, for example, you wanted to use this script to logoff the Internet,
  11&nbsp;#     process=pppd
  12&nbsp;
  13&nbsp;t=`pidof $process`       # Find pid (process id) of $process.
  14&nbsp;# The pid is needed by 'kill' (can't 'kill' by program name).
  15&nbsp;
  16&nbsp;if [ -z "$t" ]           # If process not present, 'pidof' returns null.
  17&nbsp;then
  18&nbsp;  echo "Process $process was not running."
  19&nbsp;  echo "Nothing killed."
  20&nbsp;  exit $NOPROCESS
  21&nbsp;fi  
  22&nbsp;
  23&nbsp;kill $t                  # May need 'kill -9' for stubborn process.
  24&nbsp;
  25&nbsp;# Need a check here to see if process allowed itself to be killed.
  26&nbsp;# Perhaps another " t=`pidof $process` " or ...
  27&nbsp;
  28&nbsp;
  29&nbsp;# This entire script could be replaced by
  30&nbsp;#    kill $(pidof -x process_name)
  31&nbsp;# but it would not be as instructive.
  32&nbsp;
  33&nbsp;exit 0</PRE
></TD
></TR
></TABLE
><HR></DIV
></DD
><DT
><B
CLASS="COMMAND"
>fuser</B
></DT
><DD
><P
>Identifies the processes (by PID) that are accessing
	      a given file, set of files, or directory. May also be
	      invoked with the <TT
CLASS="OPTION"
>-k</TT
> option, which kills
	      those processes. This has interesting implications for
	      system security, especially in scripts preventing
	      unauthorized users from accessing system services.</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>fuser -u /usr/bin/vim</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>/usr/bin/vim:         3207e(bozo)</TT
>
 
 
 
 <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>fuser -u /dev/null</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>/dev/null:            3009(bozo)  3010(bozo)  3197(bozo)  3199(bozo)</TT
>
 	      </PRE
></TD
></TR
></TABLE
>
	    </P
><P
>One important application for <B
CLASS="COMMAND"
>fuser</B
> is
	     when physically inserting or removing storage media, such
	     as CD ROM disks or USB flash drives. Sometimes trying
	     a <A
HREF="system.html#UMOUNTREF"
>umount</A
> fails with a
	     <SPAN
CLASS="ERRORNAME"
>device is busy</SPAN
> error message. This
	     means that some user(s) and/or process(es) are accessing
	     the device. An <B
CLASS="COMMAND"
>fuser -um /dev/device_name</B
>
	     will clear up the mystery, so you can kill any relevant
	     processes.</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>umount /mnt/usbdrive</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>umount: /mnt/usbdrive: device is busy</TT
>
 
 
 
 <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>fuser -um /dev/usbdrive</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>/mnt/usbdrive:        1772c(bozo)</TT
>
 
 <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>kill -9 1772</B
></TT
>
 <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>umount /mnt/usbdrive</B
></TT
>
 	      </PRE
></TD
></TR
></TABLE
>
	    </P
><P
> The <B
CLASS="COMMAND"
>fuser</B
> command, invoked with the
	      <TT
CLASS="OPTION"
>-n</TT
> option identifies the processes
	      accessing a <I
CLASS="EMPHASIS"
>port</I
>. This
	      is especially useful in combination with <A
HREF="system.html#NMAPREF"
>nmap</A
>.</P
><P
>	      <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>root# </TT
><TT
CLASS="USERINPUT"
><B
>nmap localhost.localdomain</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>PORT     STATE SERVICE
 25/tcp   open  smtp</TT
>
 
 
 
 <TT
CLASS="PROMPT"
>root# </TT
><TT
CLASS="USERINPUT"
><B
>fuser -un tcp 25</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>25/tcp:               2095(root)</TT
>
 
 <TT
CLASS="PROMPT"
>root# </TT
><TT
CLASS="USERINPUT"
><B
>ps ax | grep 2095 | grep -v grep</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>2095 ?        Ss     0:00 sendmail: accepting connections</TT
>
 	      </PRE
></TD
></TR
></TABLE
>
            </P
></DD
><DT
><A
NAME="CRONREF"
></A
><B
CLASS="COMMAND"
>cron</B
></DT
><DD
><P
>Administrative program scheduler, performing such
	      duties as cleaning up and deleting system log
	      files and updating the <SPAN
CLASS="DATABASE"
>slocate</SPAN
>
	      database. This is the superuser version of <A
HREF="timedate.html#ATREF"
>at</A
> (although each user may have their
	      own <TT
CLASS="FILENAME"
>crontab</TT
> file which can be changed
	      with the <B
CLASS="COMMAND"
>crontab</B
> command).  It runs
	      as a <A
HREF="communications.html#DAEMONREF"
>daemon</A
> and executes
	      scheduled entries from <TT
CLASS="FILENAME"
>/etc/crontab</TT
>.</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
>Some flavors of Linux run
	      <B
CLASS="COMMAND"
>crond</B
>, Matthew Dillon's version of
	      <B
CLASS="COMMAND"
>cron</B
>.</P
></TD
></TR
></TABLE
></DIV
></DD
></DL
></DIV
><DIV
CLASS="VARIABLELIST"
><P
><B
><A
NAME="RUNCONTROLSYS1"
></A
>Process Control and Booting</B
></P
><DL
><DT
><B
CLASS="COMMAND"
>init</B
></DT
><DD
><P
><A
NAME="INITTABREF"
></A
></P
><P
>The <B
CLASS="COMMAND"
>init</B
> command is the <A
HREF="internal.html#FORKREF"
>parent</A
> of all processes. Called
	      in the final step of a bootup, <B
CLASS="COMMAND"
>init</B
>
	      determines the runlevel of the system from
	      <TT
CLASS="FILENAME"
>/etc/inittab</TT
>. Invoked by its alias
	      <B
CLASS="COMMAND"
>telinit</B
>, and by root only.</P
></DD
><DT
><B
CLASS="COMMAND"
>telinit</B
></DT
><DD
><P
>Symlinked to <B
CLASS="COMMAND"
>init</B
>, this is a means of changing the system runlevel,
	      usually done for system maintenance or emergency filesystem
	      rep