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>Advanced Bash-Scripting Guide: An in-depth exploration of the art of shell scripting</TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="bottom"
><A
HREF="devproc.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="80%"
ALIGN="center"
VALIGN="bottom"
>Chapter 29. <TT
CLASS="FILENAME"
>/dev</TT
> and <TT
CLASS="FILENAME"
>/proc</TT
></TD
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><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="PROCREF1"
></A
>29.2. <TT
CLASS="FILENAME"
>/proc</TT
></H1
><P
><A
NAME="PROCREF2"
></A
></P
><P
>The <TT
CLASS="FILENAME"
>/proc</TT
> directory
	is actually a pseudo-filesystem.  The files in <TT
CLASS="FILENAME"
>/proc</TT
> mirror currently running
	system and kernel <A
HREF="special-chars.html#PROCESSREF"
>processes</A
>
	and contain information and statistics about them.</P
><P
>         <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="SCREEN"
> <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>cat /proc/devices</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>Character devices:
   1 mem
   2 pty
   3 ttyp
   4 ttyS
   5 cua
   7 vcs
  10 misc
  14 sound
  29 fb
  36 netlink
 128 ptm
 136 pts
 162 raw
 254 pcmcia

 Block devices:
   1 ramdisk
   2 fd
   3 ide0
   9 md</TT
>
 
 
 
 <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>cat /proc/interrupts</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>           CPU0       
   0:      84505          XT-PIC  timer
   1:       3375          XT-PIC  keyboard
   2:          0          XT-PIC  cascade
   5:          1          XT-PIC  soundblaster
   8:          1          XT-PIC  rtc
  12:       4231          XT-PIC  PS/2 Mouse
  14:     109373          XT-PIC  ide0
 NMI:          0 
 ERR:          0</TT
>
 
 
 <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>cat /proc/partitions</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>major minor  #blocks  name     rio rmerge rsect ruse wio wmerge wsect wuse running use aveq

    3     0    3007872 hda 4472 22260 114520 94240 3551 18703 50384 549710 0 111550 644030
    3     1      52416 hda1 27 395 844 960 4 2 14 180 0 800 1140
    3     2          1 hda2 0 0 0 0 0 0 0 0 0 0 0
    3     4     165280 hda4 10 0 20 210 0 0 0 0 0 210 210
    ...</TT
>
 
 
 
 <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>cat /proc/loadavg</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>0.13 0.42 0.27 2/44 1119</TT
>
 
 
 
 <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>cat /proc/apm</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>1.16 1.2 0x03 0x01 0xff 0x80 -1% -1 ?</TT
>
 
 
 
 <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>cat /proc/acpi/battery/BAT0/info</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>present:                 yes
 design capacity:         43200 mWh
 last full capacity:      36640 mWh
 battery technology:      rechargeable
 design voltage:          10800 mV
 design capacity warning: 1832 mWh
 design capacity low:     200 mWh
 capacity granularity 1:  1 mWh
 capacity granularity 2:  1 mWh
 model number:            IBM-02K6897
 serial number:            1133
 battery type:            LION
 OEM info:                Panasonic</TT
>
  
  
  
 <TT
CLASS="PROMPT"
>bash$ </TT
><TT
CLASS="USERINPUT"
><B
>fgrep Mem /proc/meminfo</B
></TT
>
 <TT
CLASS="COMPUTEROUTPUT"
>MemTotal:       515216 kB
 MemFree:        266248 kB</TT
>
          </PRE
></TD
></TR
></TABLE
>
      </P
><P
>Shell scripts may extract data from certain of the files in
         <TT
CLASS="FILENAME"
>/proc</TT
>.

	   <A
NAME="AEN19180"
HREF="#FTN.AEN19180"
>[1]</A
></P
><P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;FS=iso                       # ISO filesystem support in kernel?
   2&nbsp;
   3&nbsp;grep $FS /proc/filesystems   # iso9660</PRE
></TD
></TR
></TABLE
></P
><P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;kernel_version=$( awk '{ print $3 }' /proc/version )</PRE
></TD
></TR
></TABLE
></P
><P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;CPU=$( awk '/model name/ {print $5}' &#60; /proc/cpuinfo )
   2&nbsp;
   3&nbsp;if [ "$CPU" = "Pentium(R)" ]
   4&nbsp;then
   5&nbsp;  run_some_commands
   6&nbsp;  ...
   7&nbsp;else
   8&nbsp;  run_other_commands
   9&nbsp;  ...
  10&nbsp;fi
  11&nbsp;
  12&nbsp;
  13&nbsp;
  14&nbsp;cpu_speed=$( fgrep "cpu MHz" /proc/cpuinfo | awk '{print $4}' )
  15&nbsp;#  Current operating speed (in MHz) of the cpu on your machine.
  16&nbsp;#  On a laptop this may vary, depending on use of battery
  17&nbsp;#+ or AC power.</PRE
></TD
></TR
></TABLE
></P
><P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;# get-commandline.sh
   3&nbsp;# Get the command-line parameters of a process.
   4&nbsp;
   5&nbsp;OPTION=cmdline
   6&nbsp;
   7&nbsp;# Identify PID.
   8&nbsp;pid=$( echo $(pidof "$1") | awk '{ print $1 }' )
   9&nbsp;# Get only first            ^^^^^^^^^^^^^^^^^^ of multiple instances.
  10&nbsp;
  11&nbsp;echo
  12&nbsp;echo "Process ID of (first instance of) "$1" = $pid"
  13&nbsp;echo -n "Command-line arguments: "
  14&nbsp;cat /proc/"$pid"/"$OPTION" | xargs -0 echo
  15&nbsp;#   Formats output:        ^^^^^^^^^^^^^^^
  16&nbsp;#   (Thanks, Han Holl, for the fixup!)
  17&nbsp;
  18&nbsp;echo; echo
  19&nbsp;
  20&nbsp;
  21&nbsp;# For example:
  22&nbsp;# sh get-commandline.sh xterm</PRE
></TD
></TR
></TABLE
></P
><P
>+</P
><P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;devfile="/proc/bus/usb/devices"
   2&nbsp;text="Spd"
   3&nbsp;USB1="Spd=12"
   4&nbsp;USB2="Spd=480"
   5&nbsp;
   6&nbsp;
   7&nbsp;bus_speed=$(fgrep -m 1 "$text" $devfile | awk '{print $9}')
   8&nbsp;#                 ^^^^ Stop after first match.
   9&nbsp;
  10&nbsp;if [ "$bus_speed" = "$USB1" ]
  11&nbsp;then
  12&nbsp;  echo "USB 1.1 port found."
  13&nbsp;  # Do something appropriate for USB 1.1.
  14&nbsp;fi</PRE
></TD
></TR
></TABLE
></P
><DIV
CLASS="NOTE"
><TABLE
CLASS="NOTE"
WIDTH="100%"
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
>It is even possible to control certain peripherals with commands
	  sent to the <TT
CLASS="FILENAME"
>/proc</TT
> directory.

          <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="SCREEN"
> 	  <TT
CLASS="PROMPT"
>root# </TT
><B
CLASS="COMMAND"
>echo on &#62; /proc/acpi/ibm/light</B
>
           </PRE
></TD
></TR
></TABLE
>

	  This turns on the <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>Thinklight</I
></SPAN
> in certain models
	  of IBM/Lenovo Thinkpads. (May not work on all Linux distros.)</P
><P
>Of course, caution is advised when writing to <TT
CLASS="FILENAME"
>/proc</TT
>.</P
></TD
></TR
></TABLE
></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 29-3. Finding the process associated with a PID</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><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 $1 -d txt | sed -ne 's/^n//p'
  82&nbsp;
  83&nbsp;# Additional commentary by Stephane Chazelas.
  84&nbsp;
  85&nbsp;exit 0</PRE
></TD
></TR
></TABLE
><HR></DIV
><DIV
CLASS="EXAMPLE"
><HR><A
NAME="CONSTAT"
></A
><P
><B
>Example 29-4. On-line connect status</B
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>   1&nbsp;#!/bin/bash
   2&nbsp;# connect-stat.sh
   3&nbsp;#  Note that this script may need modification
   4&nbsp;#+ to work with a wireless connection.
   5&nbsp;
   6&nbsp;PROCNAME=pppd        # ppp daemon
   7&nbsp;PROCFILENAME=status  # Where to look.
   8&nbsp;NOTCONNECTED=85
   9&nbsp;INTERVAL=2           # Update every 2 seconds.
  10&nbsp;
  11&nbsp;pidno=$( ps ax | grep -v "ps ax" | grep -v grep | grep $PROCNAME |
  12&nbsp;awk '{ print $1 }' )
  13&nbsp;
  14&nbsp;# Finding the process number of 'pppd', the 'ppp daemon'.
  15&nbsp;# Have to filter out the process lines generated by the search itself.
  16&nbsp;#
  17&nbsp;#  However, as Oleg Philon points out,
  18&nbsp;#+ this could have been considerably simplified by using "pidof".
  19&nbsp;#  pidno=$( pidof $PROCNAME )
  20&nbsp;#
  21&nbsp;#  Moral of the story:
  22&nbsp;#+ When a command sequence gets too complex, look for a shortcut.
  23&nbsp;
  24&nbsp;
  25&nbsp;if [ -z "$pidno" ]   # If no pid, then process is not running.
  26&nbsp;then
  27&nbsp;  echo "Not connected."
  28&nbsp;# exit $NOTCONNECTED
  29&nbsp;else
  30&nbsp;  echo "Connected."; echo
  31&nbsp;fi
  32&nbsp;
  33&nbsp;while [ true ]       # Endless loop, script can be improved here.
  34&nbsp;do
  35&nbsp;
  36&nbsp;  if [ ! -e "/proc/$pidno/$PROCFILENAME" ]
  37&nbsp;  # While process running, then "status" file exists.
  38&nbsp;  then
  39&nbsp;    echo "Disconnected."
  40&nbsp;#   exit $NOTCONNECTED
  41&nbsp;  fi
  42&nbsp;
  43&nbsp;netstat -s | grep "packets received"  # Get some connect statistics.
  44&nbsp;netstat -s | grep "packets delivered"
  45&nbsp;
  46&nbsp;
  47&nbsp;  sleep $INTERVAL
  48&nbsp;  echo; echo
  49&nbsp;
  50&nbsp;done
  51&nbsp;
  52&nbsp;exit 0
  53&nbsp;
  54&nbsp;# As it stands, this script must be terminated with a Control-C.
  55&nbsp;
  56&nbsp;#    Exercises:
  57&nbsp;#    ---------
  58&nbsp;#    Improve the script so it exits on a "q" keystroke.
  59&nbsp;#    Make the script more user-friendly in other ways.
  60&nbsp;#    Fix the script to work with wireless/DSL connections.</PRE
></TD
></TR
></TABLE
><HR></DIV
><P
><A
NAME="PROCWARNING"
></A
></P
><DIV
CLASS="WARNING"
><TABLE
CLASS="WARNING"
WIDTH="100%"
BORDER="0"
><TR
><TD
WIDTH="25"
ALIGN="CENTER"
VALIGN="TOP"
><IMG
SRC="common/warning.png"
HSPACE="5"
ALT="Warning"></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><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
></TR
></TABLE
></DIV
></DIV
><H3
CLASS="FOOTNOTES"
>Notes</H3
><TABLE
BORDER="0"
CLASS="FOOTNOTES"
WIDTH="100%"
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="5%"
><A
NAME="FTN.AEN19180"
HREF="procref1.html#AEN19180"
>[1]</A
></TD
><TD
ALIGN="LEFT"
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
></TD
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