automount usb drive and execute a script in embedded linux using udev

Today let us see how to use udev for automounting of a usb pendrive and execute some scripts to copy files..


For reference use the link given here.


Lets get started

• Ensure that udev feature was enabled during kernel configuration. Alternatively you can use mdev from busybox for same purpose. But here we see examples for udev.
• For udev we must write rules for what udev must do when a particular device is mounted. For finer understanding of udev please read the man pages.
• Make a entry in /etc/udev/rules.d/  with a file name like "10-local.rules". This is because each rules are applied in lexical order and we have to ensure our rules load before the default the default rules.
• PS. See the default rule to have an idea on how to write a rule
• i wrote my rule like this:-
• SUBSYSTEMS=="usb",DRIVERS=="usb",SYMLINK+="test_usb",RUN+="/home/usb_mount.sh"
• the values for writing this can be got from executing the command                                              udevinfo -a -p /sys/block/sda for all sda device

• A new device file /dev/test_usb is created. the script usb_mount.sh will contain the script  to execute like  mounting and copying file. 

  NOTE:Please do not use the command like 'cat' to test the script as it may not print on         console (given in refference). Instead use echo >>(redirection) text file to debug and test

  this is the script i wrote

  
  #!/bin/sh
  logfile=/home/usb_txt
  if [ "${ACTION}" = "add" ]; then 
          #mount as vfat partion
   mount -t vfat -o umask=777 /dev/cdac_usb /home/disk
        #to copy all contents of the file to an array and each can be accessed as ${variable[i]} 
   file1=($(cat /home/igate/pass.txt))
   file2=($(cat /home/disk/test.txt))
   echo password in file 1:${file1[0]}>>$logfile
   echo password in file 2:${file2[0]}>>$logfile
   if [ ${file1[0]} = ${file2[0]} ]; then
       echo 'password authenticated'>>$logfile
   for i in 1 2
   do
    ls /home/disk/${file2[$i]}
         if [ $? == 0 ]; then
            echo "file found" >>$logfile
  #this  portion ensures that the program is killed before copying 
      if (ps -A | grep ${file2[$i]} 1>/dev/null 2>/dev/null)
      then
             killall -KILL ${file2[$i]} 1>/dev/null 2>/dev/null
      echo "Stopping " ${file2[$i]}>>$logfile
      else
      echo "Failed to kill" ${file2[$i]}>>$logfile
      fi
      sleep 2
      cp -f /home/disk/${file2[$i]} /home/igate/${file2[$i]}
      if [ $? == 0 ]; then
             echo "file found" >>$logfile
      fi
     else
            echo "file not found">>$logfile
        fi
   done
   else
       echo 'password failed'>>$logfile
   fi
  umount /home/disk
  fi

  Script working:-

  It first stores all the values in the text files in arrays file1 and file2. Then it checks whether program it plans to update is not running before copying the file. All this is recorded in th ffile usb_log.txt