Enable post cache

[gullbird]

i have not option Rebuild Post Cache in admin cp
i read note
Note: This option will not be displayed if you have not enabled post caching.
however unable to locate this option to enable post caching
where is this located

[ozzy47]

ACP --> Settings --> Options --> Server Settings and Optimization Options

Then look for the setting, Cached Posts Lifespan

[gullbird]

Rebuild Post Cache still not appear in Maintenance
Cached Posts Lifespan = 1
Disable Content Caching is set to NO
Cache Node Data is set to YES

any advice