Hello !
Its a Kindle PaperWhite WiFi (sorry about the heading) serial no given below last.
I read a similar post from member cazurrito. it does not answer my situation

I followed the Jailbreak instructions exactly. for my Kindle PaperWhite WiFi which originally showed version 5.3.8. I downloaded v5.3.5 (downgraded) as per the Jailbreak instructions on
https://www.mobileread.com/forums/sho...d.php?t=198446.
i was careful to charge it first and put it into airplane mode after reading the instructions fully at first. then installed the update 5.3.5 successfully.
after updating the kindle, it showed 5.3.5 in the settings page. all OK so far.
then i installed the files extracted from kpw_jb.zip into the folders described.
(jailbreak.sh, MOBI8_DEBUG, and jailbreak.mobi) and ran the jailbreak by touching the screen after opening the jailbreak.mobi file. the jailbreak ran fine and i could also see the log file was saying OK in all its lines or steps.
but i did not see any /var/local/java/keystore/ , in fact not even a /var directory was seen when i connected to my PC in USB disk drive mode.
but other folders (python, /extensions, and /sslinks etc) could be seen !
so i created the /var/local/java/keystore myself and copied the key file into it. (the log file says it was created but i dont see it).
then i checked in /linkss/screensavers/ there was a .png file in it.
i also created another .png file with same resolution as prescribed and used the one given to me which was (758x1024x8BPP about 183KB).
and restarted after creating empty file "cover" ( later i tried with other keywords too like "last") but i never found any "autoreboot" file in this directory like i was supposed to !
further on restart option from menu, the original amazon screensavers keep appearing

i checked by connecting to my PC again the kindle. the file "last" is not there ! kindle is deleting it ?
i repeated many times, same deletion is happening.
now i am wondering if my kindle version has something to do with this and if amazon had locked in this device.
the kindle PaperWhite WiFi, i have is sr no. B024 XXXX XXXX XXXX
original firmware was 5.3.8 now it shows 53.5 (1879290013) when i downgraded in order to install the jailbreak.
i can enclose the log file too. it says OK in all lines.
I have never Jailbroken a kindle before although i have done rooting with android phones before without problems. Im using a windowsXP PC for this work.
Please help ! any suggestions ?
Raj