Apache HTTP Server: Notes about Compatibility with NCSA's Server

### Apache HTTP Server Version 1.3

# Compatibility Notes with NCSA's Server

While Apache is for the most part a drop-in replacement for NCSA's httpd, there are a couple gotcha's to watch out for. These are mostly due to the fact that the parser for config and access control files was rewritten from scratch, so certain liberties the earlier servers took may not be available here. These are all easily fixable. If you know of other problems that belong here, let us know.

Please also check the known client problems page.

1. As of Apache 1.3.1, methods named in a `<Limit>` section must be listed in upper-case. Lower- or mixed-case method names will result in a configuration error.
2. The basic mod_auth `AuthGroupFile`-specified group file format allows commas between user names - Apache does not.
3. If you follow the NCSA guidelines for setting up access restrictions based on client domain, you may well have added entries for `AuthType, AuthName, AuthUserFile` or `AuthGroupFile`. None of these are needed (or appropriate) for restricting access based on client domain. When Apache sees `AuthType` it (reasonably) assumes you are using some authorization type based on username and password. Please remove `AuthType`, it's unnecessary even for NCSA.
4. `OldScriptAlias` is no longer supported.
5. `exec cgi=""` produces reasonable malformed header responses when used to invoke non-CGI scripts.
   The NCSA code ignores the missing header (bad idea).
   Solution: write CGI to the CGI spec and use `include virtual`, or use `exec cmd=""` instead.
6. Icons for FancyIndexing broken - well, no, they're not broken, we've just upgraded the icons from flat .xbm files to pretty and much smaller .gif files, courtesy of Kevin Hughes at EIT. If you are using the same srm.conf from an old distribution, make sure you add the new AddIcon, AddIconByType, and DefaultIcon directives.
7. Apache versions before 1.2b1 will ignore the last line of configuration files if the last line does not have a trailing newline. This affects configuration files (httpd.conf, access.conf and srm.conf), and htpasswd and htgroup files.
8. Apache does not permit commas delimiting the methods in <Limit>.
9. Apache's `<VirtualHost>` treats all addresses as "optional" (i.e., the server should continue booting if it can't resolve the address). Whereas in NCSA the default is to fail booting unless an added `optional` keyword is included.
10. Apache does not implement `OnDeny`; use `ErrorDocument` instead.
11. Apache (as of 1.3) always performs the equivalent of `HostnameLookups minimal`. `minimal` is not an option to `HostnameLookups`.
12. To embed spaces in directive arguments NCSA used a backslash before the space. Apache treats backslashes as normal characters. To embed spaces surround the argument with double-quotes instead.
13. Apache does not implement the NCSA `referer` directive. See PR#968 for a few brief suggestions on alternative ways to implement the same thing under Apache.
14. Apache does not allow ServerRoot settings inside a VirtualHost container. There is only one global ServerRoot in Apache; any desired changes in paths for virtual hosts need to be made with the explicit directives, e.g., DocumentRoot, TransferLog, etc.
15. The `AddType` directive cannot be used to set the type of particular files. Instead, you can scope you directives using <Files> blocks.

More to come when we notice them....

### Apache HTTP Server Version 1.3