How can i set fee permanently via paytxfee command
You can do one thing when running bitcoin-cli paytxfee 0.1 command, you can run command to update value of paytxfee inside bitcoind.conf file.

like this:

bitcoin-cli paytxfee NEW_AMOUNT &amp;&amp; sed -i 's/paytxfee=OLD_AMOUNT/paytxfee=NEW_AMOUNT/g' ~/.bitcoin/bitcoin.conf 


This will set fee for current session also when you restart bitcoin core price will not alter.