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.
== Background ==
== Background ==
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Or use the [[#Shell_script_to_mount/unmount_JFFS2_using_block_device_emulating_MTD|automated shell script]].
Or use the [[#Shell_script_to_mount/unmount_JFFS2_using_block_device_emulating_MTD|automated shell script]].
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Edit in 2019 - Hi. I (i336_) thought I'd leave the eraseblock size off since I'm on kernel 5.1.4.
 
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My HDD promptly began seeking a lot for a few seconds (!), and I discovered this was because it was scrambling to keep up with the just-over-30,000 errors jffs had just dumped into syslog.
 
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You definitely still need the ",128KiB". :)
 
=== Kernel memory emulating an MTD device ===
=== Kernel memory emulating an MTD device ===
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== Repacking the image ==
== Repacking the image ==
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[http://maemo.org/development/documentation/manuals/2-x/howto_use_flasher_rootfs/ Using the flasher utility and creating the reference root file system]
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[http://maemo.org/development/documentation/how-tos/2-x/howto_use_flasher_rootfs.html Using the flasher utility and creating the reference root file system]
== Modifying the copy of the image ==
== Modifying the copy of the image ==
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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 should be correct for a rootfs too, because:
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== Making the jffs2 image mount faster ==
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''Dump of /proc/mtd from N800 running diablo''
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<pre>
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dev:    size  erasesize  name
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...
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mtd3: 00400000 00020000 "initfs"
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mtd4: 0f980000 00020000 "rootfs"
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</pre>
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The jffs2 image that was just created is a plain jffs2 image. That's nice and if you were to flash it, it would work fine but what you can do is use sumtool which makes an summarized JFFS2 image. An summarized JFFS2 image mounts faster than a non-summarized one.  
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As you can see, the erase size number for the rootfs and initfs is the same. Don't get put off by the 00020000 number either, 128 is the '''correct''' number for the -e mkfs.jffs2 argument.
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This can be done simply with:
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sumtool -i <input jffs2 image> -o <output jffs2 image> -e 128KiB -l -n
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== Installing on the tablet ==
== Installing on the tablet ==
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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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  ./mount_jffs2.sh rootfs.jffs2 unmount
  ./mount_jffs2.sh rootfs.jffs2 unmount
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[[Category:HowTo]]
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[[Category:HowTos]]
[[Category:Wiki page of the day]]
[[Category:Wiki page of the day]]

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