Magento 2.2.3 configuration settings don't save

[rockecom]

example: stores>configuration>sales>shipping methods 

change any fields, save config, system returns "you saved the configuration!"

but reverts back, nothing is saved.

Have tried clear cache, delete var/cache, increased memory limit to 756M

I have another magento 2 install same version, on the same server that is working ok. 

[Rahul Gupta]

@rockecom i faced the same issue and the solution is

sudo chmod 777 var/ generated/
sudo rm -rf var/cache/*

Thanks