Frequently Asked Questions Frequently Asked QuestionsHTTPd stands for HyperText Transfer Protocol (HTTP) Daemon. HTTP is a protocol with the lightness and speed necessary for a distributed collaborative hypermedia information system.
1.2) How do I install NCSA HTTPd?
Read the documentation on
NCSA HTTPd Installation.
1.3) What is CGI?
CGI stands for Common Gateway Interface. You can read an introduction and an overview.
1.4) Where can I find HTTPd for Microsoft Windows/NT
TM?
For information on Microsoft WindowsTM HTTPd, please read
this page.
For information on Microsoft Windows NT TMHTTPd , please read this page
.
Note: Since these server packages were NOT developed by NCSA, we
are not responsible for them. Our Technical Support Personnel don't
know anything about them, and will not answer any questions about them.
2.1) How do I create and process forms?
First, read
a tutorial on creating forms. Then, in order to handle the output from
your forms, read how CGI supports forms.
Note: Not all sites allow all users to run CGI scripts on their
servers. In order to run, a CGI script must be in a ScriptAlias
directory or the server must allow CGI scripts anywhere by the CGI Magic
Type convention. See the CGI Configuration
Tutorial for more information.
2.2) How do I setup a clickable imagemap?
Read the
documentation on the imagemap script and a
tutorial on graphical information maps.
2.3) How do I manage users for authentication?
Read the documentation on
managing users and a
tutorial on user authentication.
2.4) How can I perform keyword searches?
You can use WAIS as a back-end search engine. Herein, a
tutorial on WAIS and HTTP integration.
2.5) How do I set up server-side includes?
You can use server-side includes, to provide data to clients on-the-fly.
For example, the current date or the size or last modification date for a
file. Check out a
tutorial on server-side includes.
2.6) How to add environment variables?
You can add environment variables when you use POST method.
For more infomation, please read CGI
Environment Variables
2.7) What else can I do?
Read the complete documentation on
server administration and some provided step-by-step
tutorials.
This means that the server did not recognize the referenced URL (the URL
defined as the ACTION in a HTML Form) as a
CGI script. For the server to recognize the URL as a CGI script, it
must either reside in a ScriptAlias
directory or your site must allow CGI scripts anywhere. For more information,
see the CGI Configuration Tutorial.
Note: Some versions of the NCSA HTTPd server request that you mail
NCSA if you would like this feature supported in new versions of NCSA HTTPd.
Nine times out of Ten we receive requests to support this feature, when in
fact it was a misconfiguration which caused the error message. Please
verify with the owner of the script/form before asking us to fix it.
Note: Versions of NCSA HTTPd prior to 1.5 have a bug where you can't
POST to a CGI script that is using CGI anwhere using the CGI magic MIME type
that is defined in an .htaccess file.
NCSA HTTPd uses a standard BSD4 and SYSV feature known
as file descriptor passing. NCSA HTTPd supports both
the BSD and SYSV style of file descriptor passing. Linux
chose not to implement either. NCSA HTTPd 1.4.x was released
such that the standard compile was to use the NO_PASS feature,
which causes NCSA HTTPd to operate similar to the way it
did in 1.3 (albeit, it is still faster). Someone devised
a hack to use the /proc filesystem under Linux to pass the
file descriptors. By request, I included the code for
this in NCSA HTTPd. Around kernel version 1.3.17, it was
discovered that there were several possible security holes
in the /proc filesystem, so the kernel was changed to
disallow this hack. Supposedly, Linux kernels in the late
1.3.x series will support one of the standard file descriptor
passing mechanisms. I do not have access to any Linux system
past 1.2.13 (the last stable release). All such systems
I have tried work flawlessly using the /proc hack.
If (and when) Linux supports a standard file descriptor passing mechanism,
I will attempt to add support to it to the distribution.
It was also determined that at some point the standard
User of nobody in httpd.conf will cause core dumps under
more recent versions of the Linux kernel. There have been
two suggested fixes to this. 1) Change the UID for user nobody
in /etc/passwd to something other than -1 2) Create a special
user (such as www) with a UID other than -1 and change the
USER configuration of NCSA HTTPd to this user.
If you use the -d or -f command line options and attempt to restart, the
restart may fail if the paths you used were not full paths. There is an
attempt at a work around in 1.5.x. Some people have complained about
the lack of information when a restart fails. Because of the nature
of the daemon, it is generally not possible to provide the information
to the terminal from which the HUP was sent (and is not always wanted,
either). Instead, we log the restart information to the error_log.
3.2) When I submit a form, it gave me 501 error...
The error message says:
We are sorry to be unable to perform the method POST to non-script
at this time.
3.3) Can't start server with "gid error"/"setgroups"
This may be caused by the values in
User directive
and Group directive.
The default values for these two directives are all set to -1.
These values are not valid on some systems. In particular, HP-UX does not
support -1 or -2 as valid groups. By default, HP-UX defines nogroup as -2,
but the server cannot use this. Also, newer versions of Linux don't like
user/group nobody, so you have to make your own (such as www) to run under.
This is also a common problem under Solaris 2.x, and is known under AIX3.1.2.
Please consult with your system administrator to find the valid values.
NOTE: This is also one of the most common causes of core dumps and
segmentation faults. If you have such problems, changing HTTPd's User and
Group directives in httpd.conf may be the solution.
3.4) My entire system grinds to a halt after I start HTTPd.
When you run HTTPd, your system may grind to a halt, as defunct and zombie
processes take up more and more system resources. If you see this, you
have the wrong setting of BSD. You should recompile with the correct BSD
setting. For compiling information, see Compiling NCSA HTTPd.3.5) Why doesn't NCSA HTTPd work on my Linux system?
NCSA HTTPd is not crippled. Linux may be crippled.
3.6) Why does NCSA HTTPd core dump when I try to restart it?
NCSA HTTPd 1.4.x did some things in its restart code which are generally
considered a bad thing to do. Most platforms allow it anyways, but under
certain systems (most notably SunOS 4.1.3 and Solaris 2.x) using gcc with
-O2 optimization, the restart code causes a SIGBUS. NCSA HTTPd 1.4.2
worked "around" this problem by changing the default compile to -O
optimization. NCSA HTTPd 1.5.x had a complete change in the way in
which restarts were handled to work in a fashion which didn't bend the
rules, and there should be no more problems with the restart.
4.1) Does NCSA HTTPd support server push?
The short answer is yes. NCSA HTTPd 1.4.x required server push CGI scripts
to be nph- scripts (see nph documentation).
This should not be necessary in NCSA HTTPd 1.5.
4.2) My images seem to come in chunks under server push.
In order to make server push work, you have to use non-buffered I/O.
In Perl, this can be done by adding $|=1; somewhere before
you start sending data. Under C, just use write instead of printf.
4.3) I can't get my ErrorDocument for 401
Errors to work.
In order for 401 Error messages to be correctly handled, an extra
header giving information about what is required for authentication
is required, the WWW-Authenticate header. Currently, the server
does not automatically add this header to user specified ErrorDocuments,
so a CGI script must be used, and it must add the WWW-Authenticate header
on its own. See the nph-error.pl example.
4.4) What does that "501 -- Not Implemented" error mean?
NCSA HTTPd fully supports the POST, GET, and PUT methods. Under most
circumstances, the problem is not that the HTML uses an unimplemented
method, but that it uses the proper method on a file that cannot accept it.
If you see this error on a a page which is NOT your own, then you have
two major courses of action:
If this is your own page, then you can do the following:
For more information on setting up CGI scripts, check the following URLs:
4.5) Why isn't REMOTE_USER set for protected directories?
This is usually asked for CGI scripts which use the POST method. As shown
in the User Authentication Tutorial, you need
to use the Limit directive to limit the
directory. The Limit directive takes as arguments which methods need to be
limited. So, to make sure you are protecting against a POST to a directory,
you need the following:
<Limit GET HEAD POST>
require valid-user
</Limit>
5.1) Can I have hidden variables in forms?
Actually this is handled by the browser (e.g. NCSA Mosaic). In any
case, there is an
example with hidden variables in the documentation.
5.2) Can I have multiple submit buttons?
This is also handled by your browser. NCSA Mosaic for X as of v2.5 has
support for multiple submit buttons. See an
example to learn how to use them.
5.3) What is PGP/PEM encryption?
PGP and PEM are programs to allow you and a second party to communicate in a
way which does not allow third parties to read your messages. For more
information, there is a PGP/PEM FAQ.
5.4) Can I have my server use multiple names?
Yes, you can -- one of the new features of HTTPd 1.5 is a VirtualHost
directive which implements just this. Be aware, though, that any names
you use must be valid Domain Name Server entries. For more information,
see the
VirtualHost tutorial.
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