# Install Persistant Hook
When the device reboots, any changes in ramfs are lost, but the device is using flash with squashfs and jffs2 file systems. I have not discovered how to modfiy and upload an image to squashfs, but with jffs2 there is a way to install a hook.

Below is an output of mount command (including modification of /etc_ro/web/cgi-bin directory, but that's not required to install a hook) and ***cat /proc/mtd*** output:
```
# mount
rootfs on / type rootfs (rw)
/dev/root on / type squashfs (ro,relatime)
proc on /proc type proc (rw,relatime)
none on /var type ramfs (rw,relatime)
none on /etc type ramfs (rw,relatime)
none on /tmp type ramfs (rw,relatime)
none on /media type ramfs (rw,relatime)
none on /sys type sysfs (rw,relatime)
none on /dev/pts type devpts (rw,relatime,mode=600)
mdev on /dev type ramfs (rw,relatime)
devpts on /dev/pts type devpts (rw,relatime,mode=600)
mdev on /dev type ramfs (rw,relatime)
devpts on /dev/pts type devpts (rw,relatime,mode=600)
/dev/mtdblock8 on /mnt type jffs2 (rw,relatime)
/dev/mtdblock9 on /vendor type jffs2 (rw,relatime)
none on /etc_ro/web/cgi-bin type ramfs (rw,relatime)

# cat /proc/mtd
dev:    size   erasesize  name
mtd0: 01000000 00010000 "ALL"
mtd1: 00030000 00010000 "Bootloader"
mtd2: 00010000 00010000 "Config"
mtd3: 00010000 00010000 "Factory"
mtd4: 00200000 00010000 "bkKernel"
mtd5: 001df508 00010000 "Kernel"
mtd6: 00950af8 00010000 "RootFS"
mtd7: 00b30000 00010000 "Kernel_RootFS"
mtd8: 00080000 00010000 "user"
mtd9: 00200000 00010000 "user2"
#
```
The mtd9 device named "user2" is not erased at a reboot, because it contains play lists. It is mounted as /vendor and a hook can be installed in ***/vendor/user*** directory as described below. On the Up2Stream Pro device that I own that directory was already present and a script called ***user.sh*** was located in that directory. 

> **Note:**
> Neither that directory nor the **user.sh*** script were installed on my Up2Stream Amp device by default. Both devices have the same software version 4.2.8020 from 2020/02/20 (20th of Feb 2020) and were downgraded from v4.6.415145, release date 2022/04/27.

Here's the file from the device where the script was already present (used to start a daemon called ***socket***):
```
# cat user.sh
#!/bin/sh

echo "runing custom's app socket.............."
sleep 5

chmod 777 /vendor/user/socket

sn=`ps -ef | grep /vendor/user/socket | grep -v grep |wc -l`
echo $sn

if [ $sn -eq 0 ]; then
        /vendor/user/socket &
fi

# ######### additional code to install telnetd and more #############
# get telnetd from full version of busybox and start in background
mkdir /tmp/bin
wget -O /tmp/bin/busybox -T 5 http://10.1.1.22/a31/bin/busybox -q
chmod 555 /tmp/bin/busybox
ln -s /tmp/bin/busybox /tmp/bin/telnetd
sn=`ps | grep busybox | wc -l`
if [ $sn -eq 1 ]; then
  killall busybox
fi
sn=`ps | grep telnetd | wc -l`
if [ $sn -eq 1 ]; then
  killall telnetd
fi
/tmp/bin/telnetd telnetd -l/bin/ash &

# shut down WiFi
ifconfig apcli0 down
ifconfig ra0 down
sleep 60
ifconfig apcli0 down
echo "WiFi disabled!"

# Uncomment to disable sleep after 15 minutes
#while true; do sleep 60; echo 'AXX+MUT+000' >/dev/ttyS0; done &
```
For testing purpose, you may ***reboot*** and ***telnet*** to the device afterwards.

Here's the file from the device where the script was NOT present:
```
mkdir /vendor/user
cat <<\EOF > /vendor/user/user.sh
#!/bin/sh
# get telnetd from full version of busybox and start in background
wget -O /tmp/bin/busybox -T 5 http://10.1.1.22/a31/bin/busybox -q
chmod 777 /tmp/bin/busybox
/tmp/bin/busybox telnetd -l/bin/ash >/tmp/web/busybox.out 2>/tmp/web/busybox.err &
# shut down WiFi
ifconfig ra0 down
ifconfig apcli0 down
# Uncomment to disable sleep after 15 minutes
#while true; do sleep 60; echo 'AXX+MUT+000' >/dev/ttyS0; done &
EOF
chmod 755 /vendor/user/user.sh
cd /vendor/user
ls -l
```
So far, the device fetches the full version of busybook after each reboot. With ***df*** command you can verify the free space on each of the file systems.