Editing Modifying the root image

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This article describes two methods for extending and modifying an existing tablet JFFS2 root image. Note that this article does not work with the "root.jffs2" file for the [[Nokia N900|N900]], as despite the filename, the N900 does not use jffs2. See http://talk.maemo.org/showpost.php?p=403015&postcount=3 for a solution for N900.
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This article describes two methods for extending and modifying an existing tablet JFFS2 root image. Note that this article does not work with the "root.jffs2" file for the N900, as despite the filename, the N900 does not use jffs2. See http://talk.maemo.org/showpost.php?p=403015&postcount=3 for a solution for N900.
== Background ==
== Background ==
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:<pre> sudo mkfs.jffs2 -r myRootImage -o myRootImage.jffs2 -e 128 -l -n </pre>
:<pre> sudo mkfs.jffs2 -r myRootImage -o myRootImage.jffs2 -e 128 -l -n </pre>
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Where ''myRootImage'' is the root of your new filesystem and ''myRootImage.jffs2'' is the name of the output file. -e 128 specifies a erase size of 128 KiB. 128 KiB is the correct erase size for the initfs. It is correct for an rootfs too.
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Where ''myRootImage'' is the root of your new filesystem and ''myRootImage.jffs2'' is the name of the output file. -e 128 specifies a erase size of 128KiB. 128KiB is the correct erase size for the initfs. It is correct for an rootfs too.
== Making the jffs2 image mount faster ==
== Making the jffs2 image mount faster ==
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== Shell script to mount/unmount JFFS2 using block device emulating MTD ==
== Shell script to mount/unmount JFFS2 using block device emulating MTD ==
Create a shell script (mount_jffs2.sh) from the following:
Create a shell script (mount_jffs2.sh) from the following:
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<source lang="bash">
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<pre>
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#!/bin/sh
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#!/bin/sh
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JFFSIMG=$1 # jffs image
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JFFSIMG=$1 # jffs image
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LOOP="/dev/loop1" # loop device
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LOOP="/dev/loop1" # loop device
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MP="/media/jffs2" # mount point
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MP="/media/jffs2" # mount point
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MTDBLOCK="/tmp/mtdblock0" # MTD device file
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MTDBLOCK="/tmp/mtdblock0" # MTD device file
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KVER="2.6"
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KVER="2.6"
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BLKMTD="block2mtd"
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BLKMTD="block2mtd"
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UMNT=""
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UMNT=""
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echo "$0" | grep unmount_ >/dev/null 2>&1
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echo "$0" | grep unmount_ >/dev/null 2>&1
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[ $? -eq 0 ] && UMNT=1
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[ $? -eq 0 ] && UMNT=1
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if [ $# -gt 1 -a x"$2"x = x"unmount"x ]; then
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if [ $# -gt 1 -a x"$2"x = x"unmount"x ]; then
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  UMNT=1
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  UMNT=1
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fi
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fi
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uname -r | egrep '^2\.6' >/dev/null 2>&1
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uname -r | egrep '^2\.6' >/dev/null 2>&1
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if [ $? -ne 0 ]; then
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if [ $? -ne 0 ]; then
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  KVER="2.4"
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  KVER="2.4"
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  BLKMTD=blkmtd
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  BLKMTD=blkmtd
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fi  
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fi  
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if [ x"${UMNT}"x = x""x ]; then
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if [ x"${UMNT}"x = x""x ]; then
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  if [ ! -b ${MTDBLOCK} ] ; then
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  if [ ! -b ${MTDBLOCK} ] ; then
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    mknod ${MTDBLOCK} b 31 0 || exit 1
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    mknod ${MTDBLOCK} b 31 0 || exit 1
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  fi
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  fi
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  lsmod | grep loop >/dev/null 2>&1
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  lsmod | grep loop >/dev/null 2>&1
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  if [ $? -ne 0 ]; then
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  if [ $? -ne 0 ]; then
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    modprobe loop
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    modprobe loop
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    [ $? -ne 0 ] && echo "loopback loading failed" && exit 1
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    [ $? -ne 0 ] && echo "loopback loading failed" && exit 1
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    sleep 1
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    sleep 1
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  fi
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  fi
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  losetup ${LOOP} ${JFFSIMG} || exit 1
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  losetup ${LOOP} ${JFFSIMG} || exit 1
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  sleep 1
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  sleep 1
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  modprobe mtdblock
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  modprobe mtdblock
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  if [ x"${KVER}"x = x"2.4"x ]; then
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  if [ x"${KVER}"x = x"2.4"x ]; then
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    modprobe ${BLKMTD} device=${LOOP} || exit 1
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    modprobe ${BLKMTD} device=${LOOP} || exit 1
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  else
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  else
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    modprobe ${BLKMTD} || exit 1
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    modprobe ${BLKMTD} || exit 1
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    echo "${LOOP}" > /sys/module/block2mtd/parameters/block2mtd
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    echo "${LOOP}" > /sys/module/block2mtd/parameters/block2mtd
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  fi
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  fi
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  sleep 1
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  sleep 1
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  modprobe jffs2
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  modprobe jffs2
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  [ ! -d ${MP} ] && mkdir -p ${MP}
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  [ ! -d ${MP} ] && mkdir -p ${MP}
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  mount -t jffs2 ${MTDBLOCK} ${MP} || exit 1
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  mount -t jffs2 ${MTDBLOCK} ${MP} || exit 1
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else
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else
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  umount ${MP}
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  umount ${MP}
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  if [ $? -ne 0 ]; then
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  if [ $? -ne 0 ]; then
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    echo "Cannot unmount JFFS2 at $MP" && exit 1
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    echo "Cannot unmount JFFS2 at $MP" && exit 1
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  fi
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  fi
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  modprobe -r jffs2
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  modprobe -r jffs2
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  modprobe -r ${BLKMTD}
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  modprobe -r ${BLKMTD}
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  modprobe -r mtdblock
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  modprobe -r mtdblock
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  sleep 1
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  sleep 1
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  losetup -d ${LOOP}
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  losetup -d ${LOOP}
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fi  
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fi  
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</source>
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</pre>
Make sure you chmod a+x mount_jffs2.sh to make the shell script executable.
Make sure you chmod a+x mount_jffs2.sh to make the shell script executable.
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== Shell script to mount/unmount JFFS2 using kernel memory emulating MTD ==
== Shell script to mount/unmount JFFS2 using kernel memory emulating MTD ==
Create a shell script (mount_jffs2.sh) from the following:
Create a shell script (mount_jffs2.sh) from the following:
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<source lang="bash">
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<pre>
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#!/bin/sh
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#!/bin/sh
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JFFSIMG=$1 # jffs image
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JFFSIMG=$1 # jffs image
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MP="/media/jffs2" # mount point
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MP="/media/jffs2" # mount point
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MTDBLOCK="/tmp/mtdblock0" # MTD device file
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MTDBLOCK="/tmp/mtdblock0" # MTD device file
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UMNT=""
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UMNT=""
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echo "$0" | grep unmount_ >/dev/null 2>&1
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echo "$0" | grep unmount_ >/dev/null 2>&1
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[ $? -eq 0 ] && UMNT=1
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[ $? -eq 0 ] && UMNT=1
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if [ $# -gt 1 -a x"$2"x = x"unmount"x ]; then
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if [ $# -gt 1 -a x"$2"x = x"unmount"x ]; then
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  UMNT=1
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  UMNT=1
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fi
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fi
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if [ x"${UMNT}"x = x""x ]; then
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if [ x"${UMNT}"x = x""x ]; then
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  if [ ! -b ${MTDBLOCK} ] ; then
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  if [ ! -b ${MTDBLOCK} ] ; then
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    mknod ${MTDBLOCK} b 31 0 || exit 1
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    mknod ${MTDBLOCK} b 31 0 || exit 1
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  fi
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  fi
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  modprobe mtdblock
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  modprobe mtdblock
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  modprobe mtdram total_size=65536 erase_size=256
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  modprobe mtdram total_size=65536 erase_size=256
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  modprobe jffs2
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  modprobe jffs2
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  dd if=${JFFSIMG} of=${MTDBLOCK}
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  dd if=${JFFSIMG} of=${MTDBLOCK}
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  [ ! -d ${MP} ] && mkdir -p ${MP}
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  [ ! -d ${MP} ] && mkdir -p ${MP}
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  mount -t jffs2 ${MTDBLOCK} ${MP}
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  mount -t jffs2 ${MTDBLOCK} ${MP}
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else
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else
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  umount ${MP}
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  umount ${MP}
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  if [ $? -ne 0 ]; then
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  if [ $? -ne 0 ]; then
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    echo "Cannot unmount JFFS2 at $MP" && exit 1
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    echo "Cannot unmount JFFS2 at $MP" && exit 1
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  fi
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  fi
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  modprobe -r jffs2
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  modprobe -r jffs2
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  modprobe -r mtdram
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  modprobe -r mtdram
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  modprobe -r mtdblock
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  modprobe -r mtdblock
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fi  
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fi  
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</source>
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</pre>
Make sure you chmod a+x mount_jffs2.sh to make the shell script executable.
Make sure you chmod a+x mount_jffs2.sh to make the shell script executable.
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You can also use this script to unmount and unload the non-utilized kernel modules:
You can also use this script to unmount and unload the non-utilized kernel modules:
  ./mount_jffs2.sh rootfs.jffs2 unmount
  ./mount_jffs2.sh rootfs.jffs2 unmount
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[[Category:HowTo]]
[[Category:HowTo]]
[[Category:Wiki page of the day]]
[[Category:Wiki page of the day]]

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