Manual:UpdateSearchIndex.php

updateSearchIndex.php is a used for periodic off-peak updating of the search index for the recently changed pages. If you need to rebuild the search index entirely, run instead.

Invocation
php maintenance/updateSearchIndex.php [-s start-timestamp] [-e end-timestamp] [-p posfile] [-l locktime] [-q]

Write permissions
The script will write the end timestamp on the file specified by the parameter, that will default to. The script will fail if the user executing the command doesn't have permissions to write to that file. To prevent the error, specify a file with write permissions, or create the file yourself and give it the appropriate permissions.