procref1.html

Shall高级编程

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><P
>It is even possible to control certain peripherals with commands
	  sent to the <TT
CLASS="FILENAME"
>/proc</TT
> directory.

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><PRE
CLASS="SCREEN"
> 	  <TT
CLASS="PROMPT"
>root# </TT
><B
CLASS="COMMAND"
>echo on &#62; /proc/acpi/ibm/light</B
>
           </PRE
></TD
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>

	  This turns on the <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>Thinklight</I
></SPAN
> in certain models
	  of IBM/Lenovo Thinkpads.</P
><P
>Of course, caution is advised when writing to <TT
CLASS="FILENAME"
>/proc</TT
>.</P
></TD
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></DIV
><P
><A
NAME="PROCRUNNING"
></A
></P
><P
>The <TT
CLASS="FILENAME"
>/proc</TT
> directory
	   contains subdirectories with unusual numerical
	   names.  Every one of these names maps to the <A
HREF="variables2.html#PPIDREF"
>process ID</A
> of a currently running
	   process.  Within each of these subdirectories, there are
	   a number of files that hold useful information about the
	   corresponding process.  The <TT
CLASS="FILENAME"
>stat</TT
> and
	   <TT
CLASS="FILENAME"
>status</TT
> files keep running statistics
	   on the process, the <TT
CLASS="FILENAME"
>cmdline</TT
> file holds
	   the command-line arguments the process was invoked with, and
	   the <TT
CLASS="FILENAME"
>exe</TT
> file is a symbolic link to the
	   complete path name of the invoking process. There are a few
	   more such files, but these seem to be the most interesting
	   from a scripting standpoint.</P
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="PIDID"
></A
><P
><B
>Example 27-2. Finding the process associated with a PID</B
></P
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><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;# pid-identifier.sh:
   3&nbsp;# Gives complete path name to process associated with pid.
   4&nbsp;
   5&nbsp;ARGNO=1  # Number of arguments the script expects.
   6&nbsp;E_WRONGARGS=65
   7&nbsp;E_BADPID=66
   8&nbsp;E_NOSUCHPROCESS=67
   9&nbsp;E_NOPERMISSION=68
  10&nbsp;PROCFILE=exe
  11&nbsp;
  12&nbsp;if [ $# -ne $ARGNO ]
  13&nbsp;then
  14&nbsp;  echo "Usage: `basename $0` PID-number" &#62;&#38;2  # Error message &#62;stderr.
  15&nbsp;  exit $E_WRONGARGS
  16&nbsp;fi  
  17&nbsp;
  18&nbsp;pidno=$( ps ax | grep $1 | awk '{ print $1 }' | grep $1 )
  19&nbsp;# Checks for pid in "ps" listing, field #1.
  20&nbsp;# Then makes sure it is the actual process, not the process invoked by this script.
  21&nbsp;# The last "grep $1" filters out this possibility.
  22&nbsp;#
  23&nbsp;#    pidno=$( ps ax | awk '{ print $1 }' | grep $1 )
  24&nbsp;#    also works, as Teemu Huovila, points out.
  25&nbsp;
  26&nbsp;if [ -z "$pidno" ]  #  If, after all the filtering, the result is a zero-length string,
  27&nbsp;then                #+ no running process corresponds to the pid given.
  28&nbsp;  echo "No such process running."
  29&nbsp;  exit $E_NOSUCHPROCESS
  30&nbsp;fi  
  31&nbsp;
  32&nbsp;# Alternatively:
  33&nbsp;#   if ! ps $1 &#62; /dev/null 2&#62;&#38;1
  34&nbsp;#   then                # no running process corresponds to the pid given.
  35&nbsp;#     echo "No such process running."
  36&nbsp;#     exit $E_NOSUCHPROCESS
  37&nbsp;#    fi
  38&nbsp;
  39&nbsp;# To simplify the entire process, use "pidof".
  40&nbsp;
  41&nbsp;
  42&nbsp;if [ ! -r "/proc/$1/$PROCFILE" ]  # Check for read permission.
  43&nbsp;then
  44&nbsp;  echo "Process $1 running, but..."
  45&nbsp;  echo "Can't get read permission on /proc/$1/$PROCFILE."
  46&nbsp;  exit $E_NOPERMISSION  # Ordinary user can't access some files in /proc.
  47&nbsp;fi  
  48&nbsp;
  49&nbsp;# The last two tests may be replaced by:
  50&nbsp;#    if ! kill -0 $1 &#62; /dev/null 2&#62;&#38;1 # '0' is not a signal, but
  51&nbsp;                                      # this will test whether it is possible
  52&nbsp;                                      # to send a signal to the process.
  53&nbsp;#    then echo "PID doesn't exist or you're not its owner" &#62;&#38;2
  54&nbsp;#    exit $E_BADPID
  55&nbsp;#    fi
  56&nbsp;
  57&nbsp;
  58&nbsp;
  59&nbsp;exe_file=$( ls -l /proc/$1 | grep "exe" | awk '{ print $11 }' )
  60&nbsp;# Or       exe_file=$( ls -l /proc/$1/exe | awk '{print $11}' )
  61&nbsp;#
  62&nbsp;#  /proc/pid-number/exe is a symbolic link
  63&nbsp;#+ to the complete path name of the invoking process.
  64&nbsp;
  65&nbsp;if [ -e "$exe_file" ]  #  If /proc/pid-number/exe exists,
  66&nbsp;then                   #+ then the corresponding process exists.
  67&nbsp;  echo "Process #$1 invoked by $exe_file."
  68&nbsp;else
  69&nbsp;  echo "No such process running."
  70&nbsp;fi  
  71&nbsp;
  72&nbsp;
  73&nbsp;#  This elaborate script can *almost* be replaced by
  74&nbsp;#       ps ax | grep $1 | awk '{ print $5 }'
  75&nbsp;#  However, this will not work...
  76&nbsp;#+ because the fifth field of 'ps' is argv[0] of the process,
  77&nbsp;#+ not the executable file path.
  78&nbsp;#
  79&nbsp;# However, either of the following would work.
  80&nbsp;#       find /proc/$1/exe -printf '%l\n'
  81&nbsp;#       lsof -aFn -p $1 -d txt | sed -ne 's/^n//p'
  82&nbsp;
  83&nbsp;# Additional commentary by Stephane Chazelas.
  84&nbsp;
  85&nbsp;exit 0</PRE
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><HR></DIV
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="CONSTAT"
></A
><P
><B
>Example 27-3. On-line connect status</B
></P
><TABLE
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><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;
   3&nbsp;PROCNAME=pppd        # ppp daemon
   4&nbsp;PROCFILENAME=status  # Where to look.
   5&nbsp;NOTCONNECTED=65
   6&nbsp;INTERVAL=2           # Update every 2 seconds.
   7&nbsp;
   8&nbsp;pidno=$( ps ax | grep -v "ps ax" | grep -v grep | grep $PROCNAME | awk '{ print $1 }' )
   9&nbsp;# Finding the process number of 'pppd', the 'ppp daemon'.
  10&nbsp;# Have to filter out the process lines generated by the search itself.
  11&nbsp;#
  12&nbsp;#  However, as Oleg Philon points out,
  13&nbsp;#+ this could have been considerably simplified by using "pidof".
  14&nbsp;#  pidno=$( pidof $PROCNAME )
  15&nbsp;#
  16&nbsp;#  Moral of the story:
  17&nbsp;#+ When a command sequence gets too complex, look for a shortcut.
  18&nbsp;
  19&nbsp;
  20&nbsp;if [ -z "$pidno" ]   # If no pid, then process is not running.
  21&nbsp;then
  22&nbsp;  echo "Not connected."
  23&nbsp;  exit $NOTCONNECTED
  24&nbsp;else
  25&nbsp;  echo "Connected."; echo
  26&nbsp;fi
  27&nbsp;
  28&nbsp;while [ true ]       # Endless loop, script can be improved here.
  29&nbsp;do
  30&nbsp;
  31&nbsp;  if [ ! -e "/proc/$pidno/$PROCFILENAME" ]
  32&nbsp;  # While process running, then "status" file exists.
  33&nbsp;  then
  34&nbsp;    echo "Disconnected."
  35&nbsp;    exit $NOTCONNECTED
  36&nbsp;  fi
  37&nbsp;
  38&nbsp;netstat -s | grep "packets received"  # Get some connect statistics.
  39&nbsp;netstat -s | grep "packets delivered"
  40&nbsp;
  41&nbsp;
  42&nbsp;  sleep $INTERVAL
  43&nbsp;  echo; echo
  44&nbsp;
  45&nbsp;done
  46&nbsp;
  47&nbsp;exit 0
  48&nbsp;
  49&nbsp;# As it stands, this script must be terminated with a Control-C.
  50&nbsp;
  51&nbsp;#    Exercises:
  52&nbsp;#    ---------
  53&nbsp;#    Improve the script so it exits on a "q" keystroke.
  54&nbsp;#    Make the script more user-friendly in other ways.</PRE
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><P
><A
NAME="PROCWARNING"
></A
></P
><DIV
CLASS="WARNING"
><TABLE
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><IMG
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ALT="Warning"></TD
><TD
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><P
>In general, it is dangerous to
	 <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>write</I
></SPAN
> to the files in <TT
CLASS="FILENAME"
>/proc</TT
>, as this can corrupt the
	 filesystem or crash the machine.</P
></TD
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></DIV
><H3
CLASS="FOOTNOTES"
>Notes</H3
><TABLE
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><TD
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><A
NAME="FTN.AEN17612"
HREF="procref1.html#AEN17612"
>[1]</A
></TD
><TD
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VALIGN="TOP"
WIDTH="95%"
><P
>Certain system commands, such as
	     <A
HREF="system.html#PROCINFOREF"
>procinfo</A
>,
	     <A
HREF="system.html#FREEREF"
>free</A
>,
	     <A
HREF="system.html#VMSTATREF"
>vmstat</A
>,
	     <A
HREF="system.html#LSDEVREF"
>lsdev</A
>,
	     and <A
HREF="system.html#UPTIMEREF"
>uptime</A
>
	     do this as well.</P
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