thttpd is a simple, small, fast, and secure HTTP server. It doesn't have a lot of special features, but it suffices for most uses of the web, it's about as fast as the best full-featured servers (Apache, NCSA, Netscape), and it has one extremely useful feature (URL-traffic-based throttling) that no other server currently has.
All the command-line options can also be set in a config file. One advantage of using a config file is that the file can be changed, and thttpd will pick up the changes with a restart.
The syntax of the config file is simple, a series of "option" or "option=value" separated by whitespace. The option names are listed above with their corresponding command-line flags.
chroot() is a system call that restricts the program's view of the filesystem to the current directory and directories below it. It becomes impossible for remote users to access any file outside of the initial directory. The restriction is inherited by child processes, so CGI programs get it too. This is a very strong security measure, and is recommended. The only downside is that only root can call chroot(), so this means the program must be started as root. However, the last thing it does during initialization is to give up root access by becoming another user, so this is safe.
The program can also be compile-time configured to always do a chroot(), without needing the -r flag.
Note that with some other web servers, such as NCSA httpd, setting up a directory tree for use with chroot() is complicated, involving creating a bunch of special directories and copying in various files. With thttpd it's a lot easier, all you have to do is make sure any shells, utilities, and config files used by your CGI programs and scripts are available. If you have CGI disabled, or if you make a policy that all CGI programs must be written in a compiled language such as C and statically linked, then you probably don't have to do any setup at all.
However, one thing you should do is tell syslogd about the chroot tree, so that thttpd can still generate syslog messages. Check your system's syslodg man page for how to do this. In FreeBSD you would put something like this in /etc/rc.conf:
syslogd_flags="-l /usr/local/www/data/dev/log"Substitute in your own chroot tree's pathname, of course. Don't worry about creating the log socket, syslogd wants to do that itself. (You may need to create the dev directory.) In Linux the flag is -a instead of -l, and there may be other differences.
Relevant config.h option: ALWAYS_CHROOT.
thttpd supports the CGI 1.1 spec.
In order for a CGI program to be run, its name must match the pattern specified either at compile time or on the command line with the -c flag. This is a simple shell-style filename pattern. You can use * to match any string not including a slash, or ** to match any string including slashes, or ? to match any single character. You can also use multiple such patterns separated by |. The patterns get checked against the filename part of the incoming URL. Don't forget to quote any wildcard characters so that the shell doesn't mess with them.
Restricting CGI programs to a single directory lets the site administrator review them for security holes, and is strongly recommended. If there are individual users that you trust, you can enable their directories too.
If no CGI pattern is specified, neither here nor at compile time, then CGI programs cannot be run at all. If you want to disable CGI as a security measure, that's how you do it, just comment out the patterns in the config file and don't run with the -c flag.
Note: the current working directory when a CGI program gets run is the directory that the CGI program lives in. This isn't in the CGI 1.1 spec, but it's what most other HTTP servers do.
Relevant config.h options: CGI_PATTERN, CGI_TIMELIMIT, CGI_NICE, CGI_PATH, CGI_LD_LIBRARY_PATH, CGIBINDIR.
Basic Authentication is available as an option at compile time. If enabled, it uses a password file in the directory to be protected, called .htpasswd by default. This file is formatted as the familiar colon-separated username/encrypted-password pair, records delimited by newlines. The protection does not carry over to subdirectories. The utility program thtpasswd(1) is included to help create and modify .htpasswd files.
Relevant config.h option: AUTH_FILE
The throttle file lets you set maximum byte rates on URLs or URL groups. You can optionally set a minimum rate too. The format of the throttle file is very simple. A # starts a comment, and the rest of the line is ignored. Blank lines are ignored. The rest of the lines should consist of a pattern, whitespace, and a number. The pattern is a simple shell-style filename pattern, using ?/**/*, or multiple such patterns separated by |.
The numbers in the file are byte rates, specified in units of bytes per second. For comparison, a v.90 modem gives about 5000 B/s depending on compression, a double-B-channel ISDN line about 12800 B/s, and a T1 line is about 150000 B/s. If you want to set a minimum rate as well, use number-number.
# throttle file for www.acme.com ** 2000-100000 # limit total web usage to 2/3 of our T1, # but never go below 2000 B/s **.jpg|**.gif 50000 # limit images to 1/3 of our T1 **.mpg 20000 # and movies to even less jef/** 20000 # jef's pages are too popular
Throttling is implemented by checking each incoming URL filename against all of the patterns in the throttle file. The server accumulates statistics on how much bandwidth each pattern has accounted for recently (via a rolling average). If a URL matches a pattern that has been exceeding its specified limit, then the data returned is actually slowed down, with pauses between each block. If that's not possible (e.g. for CGI programs) or if the bandwidth has gotten way larger than the limit, then the server returns a special code saying 'try again later'.
The minimum rates are implemented similarly. If too many people are trying to fetch something at the same time, throttling may slow down each connection so much that it's not really useable. Furthermore, all those slow connections clog up the server, using up file handles and connection slots. Setting a minimum rate says that past a certain point you should not even bother - the server returns the 'try again later" code and the connection isn't even started.
There is no provision for setting a maximum connections/second throttle, because throttling a request uses as much cpu as handling it, so there would be no point. There is also no provision for throttling the number of simultaneous connections on a per-URL basis. However you can control the overall number of connections for the whole server very simply, by setting the operating system's per-process file descriptor limit before starting thttpd. Be sure to set the hard limit, not the soft limit.
Multihoming means using one machine to serve multiple hostnames. For instance, if you're an internet provider and you want to let all of your customers have customized web addresses, you might have www.joe.acme.com, www.jane.acme.com, and your own www.acme.com, all running on the same physical hardware. This feature is also known as "virtual hosts". There are three steps to setting this up.
One, make DNS entries for all of the hostnames. The current way to do this, allowed by HTTP/1.1, is to use CNAME aliases, like so:
www.acme.com IN A 188.8.131.52 www.joe.acme.com IN CNAME www.acme.com www.jane.acme.com IN CNAME www.acme.comHowever, this is incompatible with older HTTP/1.0 browsers. If you want to stay compatible, there's a different way - use A records instead, each with a different IP address, like so:
www.acme.com IN A 184.108.40.206 www.joe.acme.com IN A 220.127.116.11 www.jane.acme.com IN A 18.104.22.168This is bad because it uses extra IP addresses, a somewhat scarce resource. But if you want people with older browsers to be able to visit your sites, you still have to do it this way.
Step two. If you're using the modern CNAME method of multihoming, then you can skip this step. Otherwise, using the older multiple-IP-address method you must set up IP aliases or multiple interfaces for the extra addresses. You can use ifconfig(8)'s alias command to tell the machine to answer to all of the different IP addresses. Example:
ifconfig le0 www.acme.com ifconfig le0 www.joe.acme.com alias ifconfig le0 www.jane.acme.com aliasIf your OS's version of ifconfig doesn't have an alias command, you're probably out of luck (but see http://www.acme.com/software/thttpd/notes.html).
Third and last, you must set up thttpd to handle the multiple hosts. The easiest way is with the -v flag, or the ALWAYS_VHOST config.h option. This works with either CNAME multihosting or multiple-IP multihosting. What it does is send each incoming request to a subdirectory based on the hostname it's intended for. All you have to do in order to set things up is to create those subdirectories in the directory where thttpd will run. With the example above, you'd do like so:
mkdir www.acme.com www.joe.acme.com www.jane.acme.comIf you're using old-style multiple-IP multihosting, you should also create symbolic links from the numeric addresses to the names, like so:
ln -s www.acme.com 22.214.171.124 ln -s www.joe.acme.com 126.96.36.199 ln -s www.jane.acme.com 188.8.131.52This lets the older HTTP/1.0 browsers find the right subdirectory.
There's an optional alternate step three if you're using multiple-IP multihosting: run a separate thttpd process for each hostname, using the -h flag to specify which one is which. This gives you more flexibility, since you can run each of these processes in separate directories, with different throttle files, etc. Example:
thttpd -r -d /usr/www -h www.acme.com thttpd -r -d /usr/www/joe -u joe -h www.joe.acme.com thttpd -r -d /usr/www/jane -u jane -h www.jane.acme.comBut remember, this multiple-process method does not work with CNAME multihosting - for that, you must use a single thttpd process with the -v flag.
thttpd lets you define your own custom error pages for the various HTTP errors. There's a separate file for each error number, all stored in one special directory. The directory name is "errors", at the top of the web directory tree. The error files should be named "errNNN.html", where NNN is the error number. So for example, to make a custom error page for the authentication failure error, which is number 401, you would put your HTML into the file "errors/err401.html". If no custom error file is found for a given error number, then the usual built-in error page is generated.
If you're using the virtual hosts option, you can also have different custom error pages for each different virtual host. In this case you put another "errors" directory in the top of that virtual host's web tree. thttpd will look first in the virtual host errors directory, and then in the server-wide errors directory, and if neither of those has an appropriate error file then it will generate the built-in error.
Sometimes another site on the net will embed your image files in their HTML files, which basically means they're stealing your bandwidth. You can prevent them from doing this by using non-local referer filtering. With this option, certain files can only be fetched via a local referer. The files have to be referenced by a local web page. If a web page on some other site references the files, that fetch will be blocked. There are three config-file variables for this feature:
urlpat=**.jpg|**.gif|**.au|**.wavFor most sites, that one setting is all you need to enable referer filtering.
thttpd can be configured to expand base paths of the form /~user/ into proper references to the user's web directory.
If thttpd is compiled with the option TILDE_MAP_1 (this is the out-of-the-box default when you build from source), ~user is mapped to prefix/user where the prefix might be something like /users.
If thttpd is compiled with the option TILDE_MAP_2, ~user is mapped to a subdirectory in the user's home directory; the subdirectory's name is also configurable, but the default is public_html. This arrangement is incompatible with the chroot option, and generally considered a security risk.
See also the next section about symbolic links for additional discussion.
thttpd is very picky about symbolic links. Before delivering any file, it first checks each element in the path to see if it's a symbolic link, and expands them all out to get the final actual filename. Along the way it checks for things like links with ".." that go above the server's directory, and absolute symlinks (ones that start with a /). These are prohibited as security holes, so the server returns an error page for them. This means you can't set up your web directory with a bunch of symlinks pointing to individual users' home web directories. Instead you do it the other way around - the user web directories are real subdirs of the main web directory, and in each user's home dir there's a symlink pointing to their actual web dir.
The CGI pattern is also affected - it gets matched against the fully-expanded filename. So, if you have a single CGI directory but then put a symbolic link in it pointing somewhere else, that won't work. The CGI program will be treated as a regular file and returned to the client, instead of getting run. This could be confusing.
thttpd is also picky about file permissions. It wants data files (HTML, images) to be world readable. Readable by the group that the thttpd process runs as is not enough - thttpd checks explicitly for the world-readable bit. This is so that no one ever gets surprised by a file that's not set world-readable and yet somehow is readable by the HTTP server and therefore the *whole* world.
The same logic applies to directories. As with the standard Unix "ls" program, thttpd will only let you look at the contents of a directory if its read bit is on; but as with data files, this must be the world-read bit, not just the group-read bit.
thttpd also wants the execute bit to be *off* for data files. A file that is marked executable but doesn't match the CGI pattern might be a script or program that got accidentally left in the wrong directory. Allowing people to fetch the contents of the file might be a security breach, so this is prohibited. Of course if an executable file *does* match the CGI pattern, then it just gets run as a CGI.
In summary, data files should be mode 644 (rw-r--r--), directories should be 755 (rwxr-xr-x) if you want to allow indexing and 711 (rwx--x--x) to disallow it, and CGI programs should be mode 755 (rwxr-xr-x) or 711 (rwx--x--x).
thttpd does all of its logging via syslog(3). The facility it uses is configurable. Aside from error messages, there are only a few log entry types of interest, all fairly similar to CERN Common Log Format:
Aug 6 15:40:34 acme thttpd: 184.108.40.206 - - "GET /file" 200 357 Aug 6 15:40:43 acme thttpd: 220.127.116.11 - - "HEAD /file" 200 0 Aug 6 15:41:16 acme thttpd: referer http://www.acme.com/ -> /dir Aug 6 15:41:16 acme thttpd: user-agent Mozilla/1.1NThe package includes a script for translating these log entries info CERN-compatible files. Note that thttpd does not translate numeric IP addresses into domain names. This is both to save time and as a minor security measure (the numeric address is harder to spoof).
Relevant config.h option: LOG_FACILITY.
If you'd rather log directly to a file, you can use the -l command-line flag. But note that error messages still go to syslog.
thttpd handles a couple of signals, which you can send via the standard Unix kill(1) command:
Many thanks to contributors, reviewers, testers: John LoVerso, Jordan Hayes, Chris Torek, Jim Thompson, Barton Schaffer, Geoff Adams, Dan Kegel, John Hascall, Bennett Todd, KIKUCHI Takahiro, Catalin Ionescu. Special thanks to Craig Leres for substantial debugging and development, and for not complaining about my coding style very much.