Merge pull request #1841 from mtmail/faq-entry-about-rebuilding-nominatim-so

FAQ addition when to rebuild nominatim.so

diff --combined docs/admin/Faq.md
index 2bf0e6bee793fda6703bf1b45fd6c22fd8879b17,d2dbdda24b2643bdb2d1059cd69a20a9a4d04d34..bca6b49ddd6c6fae26da3df26ce6611c7e179c62
--- 1/docs/admin/Faq.md
--- 2/docs/admin/Faq.md
+++ b/docs/admin/Faq.md
@@@ -22,21 -22,6 +22,21 @@@ then you can resume with the following 
  If the reported rank is 26 or higher, you can also safely add `--index-noanalyse`.
  
  
 +### PostgreSQL crashed "invalid page in block"
 +
 +Usually serious problem, can be a hardware issue, not all data written to disc
 +for example. Check PostgreSQL log file and search PostgreSQL issues/mailing
 +list for hints.
 +
 +If it happened during index creation you can try rerunning the step with
 +
 +```sh
 +./utils/setup.php --create-search-indices --ignore-errors
 +```
 +
 +Otherwise it's best to start the full setup from the beginning.
 +
 +
  ### PHP "open_basedir restriction in effect" warnings
  
      PHP Warning:  file_get_contents(): open_basedir restriction in effect.
@@@ -53,7 -38,7 +53,7 @@@ by adding ";" at the beginning of the l
  again once you are done with the PHP command line operations.
  
  
- ### PHP timzeone warnings
+ ### PHP timezeone warnings
  
  The Apache log may contain lots of PHP warnings like this:
      `PHP Warning:  date_default_timezone_set() function.`
@@@ -171,7 -156,8 +171,8 @@@ Example error messag
  
  The PostgreSQL database, i.e. user `postgres`, needs to have access to that file.
  
- The permission need to be read & executable by everybody, e.g.
+ The permission need to be read & executable by everybody, but not writeable
+ by everybody, e.g.
  
  ```
     -rwxr-xr-x 1 nominatim nominatim 297984 build/module/nominatim.so
@@@ -182,6 -168,16 +183,16 @@@ Try `chmod a+r nominatim.so; chmod a+x 
  When running SELinux, make sure that the
  [context is set up correctly](../appendix/Install-on-Centos-7/#adding-selinux-security-settings).
  
+ When you recently updated your operating system, updated PostgreSQL to
+ a new version or moved files (e.g. the build directory) you should
+ recreate `nominatim.so`. Try
+ 
+ ```
+    cd build
+    rm -r module/
+    cmake $main_Nominatim_path && make
+ ```
+ 
  ### Setup.php fails with "DB Error: extension not found"
  
  Make sure you have the PostgreSQL extensions "hstore" and "postgis" installed.