1 Updated: December 21, 2004 (http://curl.haxx.se/docs/faq.html)
6 \___|\___/|_| \_\_____|
14 1.4 When will you make curl do XXXX ?
16 1.6 What do you get for making curl?
17 1.7 What about CURL from curl.com?
18 1.8 I have a problem who do I mail?
20 2. Install Related Problems
21 2.1 configure doesn't find OpenSSL even when it is installed
22 2.1.1 native linker doesn't find OpenSSL
23 2.1.2 only the libssl lib is missing
24 2.2 Does curl work/build with other SSL libraries?
25 2.3 Where can I find a copy of LIBEAY32.DLL?
26 2.4 Does curl support Socks (RFC 1928) ?
29 3.1 curl: (1) SSL is disabled, https: not supported
30 3.2 How do I tell curl to resume a transfer?
31 3.3 Why doesn't my posting using -F work?
32 3.4 How do I tell curl to run custom FTP commands?
33 3.5 How can I disable the Pragma: nocache header?
34 3.6 Does curl support ASP, XML, XHTML or HTML version Y?
35 3.7 Can I use curl to delete/rename a file through FTP?
36 3.8 How do I tell curl to follow HTTP redirects?
37 3.9 How do I use curl in my favorite programming language?
38 3.10 What about SOAP, WebDAV, XML-RPC or similar protocols over HTTP?
39 3.11 How do I POST with a different Content-Type?
40 3.12 Why do FTP specific features over HTTP proxy fail?
41 3.13 Why does my single/double quotes fail?
42 3.14 Does curl support javascript or pac (automated proxy config)?
43 3.15 Can I do recursive fetches with curl?
44 3.16 What certificates do I need when I use SSL?
45 3.17 How do I list the root dir of an FTP server?
48 4.1 Problems connecting to SSL servers.
49 4.2 Why do I get problems when I use & or % in the URL?
50 4.3 How can I use {, }, [ or ] to specify multiple URLs?
51 4.4 Why do I get downloaded data even though the web page doesn't exist?
52 4.5 Why do I get return code XXX from a HTTP server?
53 4.5.1 "400 Bad Request"
54 4.5.2 "401 Unauthorized"
57 4.5.5 "405 Method Not Allowed"
58 4.5.6 "301 Moved Permanently"
59 4.6 Can you tell me what error code 142 means?
60 4.7 How do I keep user names and passwords secret in Curl command lines?
62 4.9 Curl can't authenticate to the server that requires NTLM?
63 4.10 My HTTP request using HEAD, PUT or DELETE doesn't work!
64 4.11 Why does my HTTP range requests return the full document?
65 4.12 Why do I get "certificate verify failed" ?
68 5.1 Is libcurl thread-safe?
69 5.2 How can I receive all data into a large memory chunk?
70 5.3 How do I fetch multiple files with libcurl?
71 5.4 Does libcurl do Winsock initing on win32 systems?
72 5.5 Does CURLOPT_WRITEDATA and CURLOPT_READDATA work on win32 ?
73 5.6 What about Keep-Alive or persistent connections?
74 5.7 Link errors when building libcurl on Windows!
75 5.8 libcurl.so.3: open failed: No such file or directory
76 5.9 How does libcurl resolve host names?
79 6.1 I have a GPL program, can I use the libcurl library?
80 6.2 I have a closed-source program, can I use the libcurl library?
81 6.3 I have a BSD licensed program, can I use the libcurl library?
82 6.4 I have a program that uses LGPL libraries, can I use libcurl?
83 6.5 Can I modify curl/libcurl for my program and keep the changes secret?
84 6.6 Can you please change the curl/libcurl license to XXXX?
88 7.2 Who write PHP/CURL?
89 7.3 Can I perform multiple requests using the same handle?
91 ==============================================================================
97 cURL is the name of the project. The name is a play on 'Client for URLs',
98 originally with URL spelled in uppercase to make it obvious it deals with
99 URLs. The fact it can also be pronounced 'see URL' also helped, it works as
100 an abbrivation for "Client URL Request Library" or why not the recursive
101 version: "Curl URL Request Library".
103 The cURL project produces two products:
107 A free and easy-to-use client-side URL transfer library, supporting FTP,
108 FTPS, HTTP, HTTPS, GOPHER, TELNET, DICT, FILE and LDAP. libcurl supports
109 HTTPS certificates, HTTP POST, HTTP PUT, FTP uploading, kerberos, HTTP
110 form based upload, proxies, cookies, user+password authentication, file
111 transfer resume, http proxy tunneling and more!
113 libcurl is highly portable, it builds and works identically on numerous
114 platforms, including Solaris, NetBSD, FreeBSD, OpenBSD, Darwin, HPUX,
115 IRIX, AIX, Tru64, Linux, UnixWare, HURD, Windows, Amiga, OS/2, BeOs, Mac
116 OS X, Ultrix, QNX, OpenVMS, RISC OS, Novell NetWare, DOS and more...
118 libcurl is free, thread-safe, IPv6 compatible, feature rich, well
123 A command line tool for getting or sending files using URL syntax.
125 Since curl uses libcurl, it supports a range of common Internet protocols,
126 currently including HTTP, HTTPS, FTP, FTPS, GOPHER, LDAP, DICT, TELNET and
129 We pronounce curl and cURL with an initial k sound: [kurl].
131 NOTE: there are numerous sub-projects and related projects that also use the
132 word curl in the project names in various combinations, but you should take
133 notice that this FAQ is directed at the command-line tool named curl (and
134 libcurl the library), and may therefore not be valid for other curl-related
139 libcurl is a reliable and portable library which provides you with an easy
140 interface to a range of common Internet protocols.
142 You can use libcurl for free in your application, be it open source,
143 commercial or closed-source.
145 1.3 What is curl not?
147 Curl is *not* a wget clone. That is a common misconception. Never, during
148 curl's development, have we intended curl to replace wget or compete on its
149 market. Curl is targeted at single-shot file transfers.
151 Curl is not a web site mirroring program. If you want to use curl to mirror
152 something: fine, go ahead and write a script that wraps around curl to make
153 it reality (like curlmirror.pl does).
155 Curl is not an FTP site mirroring program. Sure, get and send FTP with curl
156 but if you want systematic and sequential behavior you should write a
157 script (or write a new program that interfaces libcurl) and do it.
159 Curl is not a PHP tool, even though it works perfectly well when used from
160 or with PHP (when using the PHP/CURL module).
162 Curl is not a single-OS program. Curl exists, compiles, builds and runs
163 under a wide range of operating systems, including all modern Unixes (and a
164 bunch of older ones too), Windows, Amiga, BeOS, OS/2, OS X, QNX etc.
166 1.4 When will you make curl do XXXX ?
168 We love suggestions of what to change in order to make curl and libcurl
169 better. We do however believe in a few rules when it comes to the future of
172 * Curl -- the command line tool -- is to remain a non-graphical command line
173 tool. If you want GUIs or fancy scripting capabilities, you should look
174 for another tool that uses libcurl.
176 * We do not add things to curl that other small and available tools already
177 do very fine at the side. Curl's output is fine to pipe into another
178 program or redirect to another file for the next program to interpret.
180 * We focus on protocol related issues and improvements. If you wanna do more
181 magic with the supported protocols than curl currently does, chances are
182 big we will agree. If you wanna add more protocols, we may very well
185 * If you want someone else to make all the work while you wait for us to
186 implement it for you, that is not a very friendly attitude. We spend a
187 considerable time already on maintaining and developing curl. In order to
188 get more out of us, you should consider trading in some of your time and
191 * If you write the code, chances are bigger that it will get into curl
196 curl and libcurl are not made by any single individual. Sure, Daniel
197 Stenberg writes the major parts, but other persons' submissions are
198 important and crucial. Anyone can contribute and post their changes and
199 improvements and have them inserted in the main sources (of course on the
200 condition that developers agree on that the fixes are good).
202 The list of contributors in the docs/THANKS file is only a small part of all
203 the people that every day provide us with bug reports, suggestions, ideas
206 curl is developed by a community, with Daniel at the wheel.
208 1.6 What do you get for making curl?
210 Project cURL is entirely free and open. No person gets paid for developing
211 (lib)curl. We do this voluntarily on our spare time.
213 We get some help from companies. Contactor Data hosts the curl web site,
214 Haxx owns the curl web site's domain and sourceforge.net hosts project
215 services we take advantage from, like the bug tracker. Also, some companies
216 have sponsored certain parts of the development in the past and I hope some
217 will continue to do so in the future.
219 If you want to support our project with a donation or similar, one way of
220 doing that would be to buy "gift certificates" at useful online shopping
221 sites, such as amazon.com or thinkgeek.com. Another way would be to sponsor
222 us through a banner-program or even better: by helping us coding,
223 documenting, testing etc. You're welcome to send us a buck using paypal, as
224 described here: http://curl.haxx.se/donation.html
226 1.7 What about CURL from curl.com?
228 During the summer 2001, curl.com was busy advertising their client-side
229 programming language for the web, named CURL.
231 We are in no way associated with curl.com or their CURL programming
234 Our project name curl has been in effective use since 1998. We were not the
235 first computer related project to use the name "curl" and do not claim any
236 first-hand rights to the name.
238 We recognize that we will be living in parallel with curl.com and wish them
241 1.8 I have a problem who do I mail?
243 Please do not mail any single individual unless you really need to. Keep
244 curl-related questions on a suitable mailing list. All available mailing
245 lists are listed in the MANUAL document and online at
246 http://curl.haxx.se/mail/
248 Keeping curl-related questions and discussions on mailing lists allows
249 others to join in and help, to share their ideas, contribute their
250 suggestions and spread their wisdom. Keeping discussions on public mailing
251 lists also allows for others to learn from this (both current and future
252 users thanks to the web based archives of the mailing lists), thus saving us
253 from having to repeat ourselves even more. Thanks for respecting this.
256 2. Install Related Problems
258 2.1 configure doesn't find OpenSSL even when it is installed
260 This may be because of several reasons.
262 2.1.1 native linker doesn't find openssl
265 Solaris (native cc compiler)
266 HPUX (native cc compiler)
267 SGI IRIX (native cc compiler)
268 SCO UNIX (native cc compiler)
270 When configuring curl, I specify --with-ssl. OpenSSL is installed in
271 /usr/local/ssl Configure reports SSL in /usr/local/ssl, but fails to find
272 CRYPTO_lock in -lcrypto
274 Cause: The cc for this test places the -L/usr/local/ssl/lib AFTER
275 -lcrypto, so ld can't find the library. This is due to a bug in the GNU
278 Workaround: Specifying "LDFLAGS=-L/usr/local/ssl/lib" in front of
279 ./configure places the -L/usr/local/ssl/lib early enough in the command
280 line to make things work
282 Solution submitted by: Bob Allison <allisonb@users.sourceforge.net>
284 2.1.2 only the libssl lib is missing
286 If all include files and the libcrypto lib is present, with only the
287 libssl being missing according to configure, this is mostly likely because
288 a few functions are left out from the libssl.
290 If the function names missing include RSA or RSAREF you can be certain
291 that this is because libssl requires the RSA and RSAREF libs to build.
293 See the INSTALL file section that explains how to add those libs to
294 configure. Make sure that you remove the config.cache file before you
295 rerun configure with the new flags.
297 2.2 Does curl work/build with other SSL libraries?
299 Curl has been written to use OpenSSL, although there should not be much
300 problems using a different library. If anyone does "port" curl to use a
301 different SSL library, we are of course very interested in getting the
304 2.3 Where can I find a copy of LIBEAY32.DLL?
306 That is an OpenSSL binary built for Windows.
308 Curl uses OpenSSL to do the SSL stuff. The LIBEAY32.DLL is what curl needs
309 on a windows machine to do https://. Check out the curl web site to find
310 accurate and up-to-date pointers to recent OpenSSL DLLs and other binary
313 2.4 Does curl support Socks (RFC 1928) ?
315 Yes, SOCKS5 is supported.
320 3.1 curl: (1) SSL is disabled, https: not supported
322 If you get this output when trying to get anything from a https:// server,
323 it means that the configure script couldn't find all libs and include files
324 it requires for SSL to work. If the configure script fails to find them,
325 curl is simply built without SSL support.
327 To get the https:// support into a curl that was previously built but that
328 reports that https:// is not supported, you should dig through the document
329 and logs and check out why the configure script doesn't find the SSL libs
330 and/or include files.
332 Also, check out the other paragraph in this FAQ labeled "configure doesn't
333 find OpenSSL even when it is installed".
335 3.2 How do I tell curl to resume a transfer?
337 Curl supports resumed transfers both ways on both FTP and HTTP.
341 3.3 Why doesn't my posting using -F work?
343 You can't simply use -F or -d at your choice. The web server that will
344 receive your post assumes one of the formats. If the form you're trying to
345 "fake" sets the type to 'multipart/form-data', then and only then you must
346 use the -F type. In all the most common cases, you should use -d which then
347 causes a posting with the type 'application/x-www-form-urlencoded'.
349 This is described in some detail in the MANUAL and TheArtOfHttpScripting
350 documents, and if you don't understand it the first time, read it again
351 before you post questions about this to the mailing list. Also, try reading
352 through the mailing list archives for old postings and questions regarding
355 3.4 How do I tell curl to run custom FTP commands?
357 You can tell curl to perform optional commands both before and/or after a
358 file transfer. Study the -Q/--quote option.
360 Since curl is used for file transfers, you don't use curl to just perform
361 FTP commands without transferring anything. Therefore you must always specify
362 a URL to transfer to/from even when doing custom FTP commands.
364 3.5 How can I disable the Pragma: nocache header?
366 You can change all internally generated headers by adding a replacement with
367 the -H/--header option. By adding a header with empty contents you safely
368 disable that one. Use -H "Pragma:" to disable that specific header.
370 3.6 Does curl support ASP, XML, XHTML or HTML version Y?
372 To curl, all contents are alike. It doesn't matter how the page was
373 generated. It may be ASP, PHP, Perl, shell-script, SSI or plain
374 HTML-files. There's no difference to curl and it doesn't even know what kind
375 of language that generated the page.
377 See also item 3.14 regarding javascript.
379 3.7 Can I use curl to delete/rename a file through FTP?
381 Yes. You specify custom FTP commands with -Q/--quote.
383 One example would be to delete a file after you have downloaded it:
385 curl -O ftp://download.com/coolfile -Q '-DELE coolfile'
387 3.8 How do I tell curl to follow HTTP redirects?
389 Curl does not follow so-called redirects by default. The Location: header
390 that informs the client about this is only interpreted if you're using the
391 -L/--location option. As in:
393 curl -L http://redirector.com
395 3.9 How do I use curl in my favorite programming language?
397 There exist many language interfaces/bindings for curl that integrates it
398 better with various languages. If you are fluid in a script language, you
399 may very well opt to use such an interface instead of using the command line
402 Find out more about which languages that support curl directly, and how to
403 install and use them, in the libcurl section of the curl web site:
404 http://curl.haxx.se/libcurl/
406 In February 2003, there are interfaces available for the following
407 languages: Basic, C, C++, Cocoa, Dylan, Euphoria, Java, Lua, Object-Pascal,
408 Pascal, Perl, PHP, PostgreSQL, Python, Rexx, Ruby, Scheme and Tcl. By the
409 time you read this, additional ones may have appeared!
411 3.10 What about SOAP, WebDAV, XML-RPC or similar protocols over HTTP?
413 Curl adheres to the HTTP spec, which basically means you can play with *any*
414 protocol that is built on top of HTTP. Protocols such as SOAP, WEBDAV and
415 XML-RPC are all such ones. You can use -X to set custom requests and -H to
416 set custom headers (or replace internally generated ones).
418 Using libcurl is of course just as fine and you'd just use the proper
419 library options to do the same.
421 3.11 How do I POST with a different Content-Type?
423 You can always replace the internally generated headers with -H/--header.
424 To make a simple HTTP POST with text/xml as content-type, do something like:
426 curl -d "datatopost" -H "Content-Type: text/xml" [URL]
428 3.12 Why do FTP specific features over HTTP proxy fail?
430 Because when you use a HTTP proxy, the protocol spoken on the network will
431 be HTTP, even if you specify a FTP URL. This effectively means that you
432 normally can't use FTP specific features such as FTP upload and FTP quote
435 There is one exception to this rule, and that is if you can "tunnel through"
436 the given HTTP proxy. Proxy tunneling is enabled with a special option (-p)
437 and is generally not available as proxy admins usually disable tunneling to
438 other ports than 443 (which is used for HTTPS access through proxies).
440 3.13 Why does my single/double quotes fail?
442 To specify a command line option that includes spaces, you might need to
443 put the entire option within quotes. Like in:
445 curl -d " with spaces " url.com
449 curl -d ' with spaces ' url.com
451 Exactly what kind of quotes and how to do this is entirely up to the shell
452 or command line interpreter that you are using. For most unix shells, you
453 can more or less pick either single (') or double (") quotes. For
454 Windows/DOS prompts I believe you're forced to use double (") quotes.
456 Please study the documentation for your particular environment. Examples in
457 the curl docs will use a mix of both these ones as shown above. You must
458 adjust them to work in your environment.
460 Remember that curl works and runs on more operating systems than most single
461 individuals have ever tried.
463 3.14 Does curl support javascript or pac (automated proxy config)?
465 Many web pages do magic stuff using embedded javascript. Curl and libcurl
466 have no built-in support for that, so it will be treated just like any other
469 .pac files are a netscape invention and are sometimes used by organizations
470 to allow them to differentiate which proxies to use. The .pac contents is
471 just a javascript program that gets invoked by the browser and that returns
472 the name of the proxy to connect to. Since curl doesn't support javascript,
473 it can't support .pac proxy configuration either.
475 Some work-arounds usually suggested to overcome this javascript dependency:
477 - Depending on the javascript complexity, write up a script that
478 translates it to another language and execute that.
480 - Read the javascript code and rewrite the same logic in another language.
482 - Implement a javascript interpreter, people have successfully used the
483 Mozilla javascript engine in the past.
485 - Ask your admins to stop this, for a static proxy setup or similar.
487 3.15 Can I do recursive fetches with curl?
489 No. curl itself has no code that performs recursive operations, such as
490 those performed by wget and similar tools.
492 There exist wrapper scripts with that functionality (for example the
493 curlmirror perl script), and you can write programs based on libcurl to do
494 it, but the command line tool curl itself cannot.
496 3.16 What certificates do I need when I use SSL?
498 There are three different kinds of "certificates" to keep track of when we
499 talk about using SSL-based protocols (HTTPS or FTPS) using curl or libcurl.
501 - Client certificate. The server you communicate may require that you can
502 provide this in order to prove that you actually are who you claim to be.
503 If the server doesn't require this, you don't need a client certificate.
505 - Server certificate. The server you communicate with has a server
506 certificate. You can and should verify this certficate to make sure that
507 you are truly talking to the real server and not a server impersonating
508 it. The server certificate verifaction process is made by using a
509 Certificate Authority certificate ("CA cert") that was used to sign the
510 server certificate. Server certificate verification is enabled by default
511 in curl and libcurl and is often the reason for problems as explained in
512 FAQ entry 4.12 and the SSLCERTS document
513 (http://curl.haxx.se/docs/sslcerts.html). Server certificates that are
514 "self-signed" or otherwise signed by a CA that you do not have a CA cert
515 for, cannot be verified. If the verification during a connect fails, you
516 are refused access. You then need to explicitly disable the verification
517 to connect to the server.
519 - Certificate Authority certificate ("CA cert"). You often have several CA
520 certs in a CA cert bundle that can be used to verify a server certificate
521 that was signed by one of the authorities in the bundle. curl comes with a
522 default CA cert bundle. You can override the default.
524 3.17 How do I list the root dir of an FTP server?
526 There are two ways. The way defined in the RFC is to use an encoded slash
527 in the first path part. List the "/tmp" dir like this:
529 curl ftp://ftp.sunet.se/%2ftmp/
531 or the not-quite-kosher-but-more-readable way, by simply starting the path
532 section of the URL with a slash:
534 curl ftp://ftp.sunet.se//tmp/
539 4.1 Problems connecting to SSL servers.
541 It took a very long time before we could sort out why curl had problems to
542 connect to certain SSL servers when using SSLeay or OpenSSL v0.9+. The
543 error sometimes showed up similar to:
545 16570:error:1407D071:SSL routines:SSL2_READ:bad mac decode:s2_pkt.c:233:
547 It turned out to be because many older SSL servers don't deal with SSLv3
548 requests properly. To correct this problem, tell curl to select SSLv2 from
549 the command line (-2/--sslv2).
551 There have also been examples where the remote server didn't like the SSLv2
552 request and instead you had to force curl to use SSLv3 with -3/--sslv3.
554 4.2 Why do I get problems when I use & or % in the URL?
556 In general unix shells, the & letter is treated special and when used, it
557 runs the specified command in the background. To safely send the & as a part
558 of a URL, you should quote the entire URL by using single (') or double (")
561 An example that would invoke a remote CGI that uses &-letters could be:
563 curl 'http://www.altavista.com/cgi-bin/query?text=yes&q=curl'
565 In Windows, the standard DOS shell treats the %-letter specially and you
566 need to use TWO %-letters for each single one you want to use in the URL.
568 Also note that if you want the literal %-letter to be part of the data you
569 pass in a POST using -d/--data you must encode it as '%25' (which then also
570 needs the %-letter doubled on Windows machines).
572 4.3 How can I use {, }, [ or ] to specify multiple URLs?
574 Because those letters have a special meaning to the shell, and to be used in
575 a URL specified to curl you must quote them.
577 An example that downloads two URLs (sequentially) would do:
579 curl '{curl,www}.haxx.se'
581 To be able to use those letters as actual parts of the URL (without using
582 them for the curl URL "globbing" system), use the -g/--globoff option:
584 curl -g 'www.site.com/weirdname[].html'
586 4.4 Why do I get downloaded data even though the web page doesn't exist?
588 Curl asks remote servers for the page you specify. If the page doesn't exist
589 at the server, the HTTP protocol defines how the server should respond and
590 that means that headers and a "page" will be returned. That's simply how
593 By using the --fail option you can tell curl explicitly to not get any data
594 if the HTTP return code doesn't say success.
596 4.5 Why do I get return code XXX from a HTTP server?
598 RFC2616 clearly explains the return codes. This is a short transcript. Go
599 read the RFC for exact details:
601 4.5.1 "400 Bad Request"
603 The request could not be understood by the server due to malformed
604 syntax. The client SHOULD NOT repeat the request without modifications.
606 4.5.2 "401 Unauthorized"
608 The request requires user authentication.
610 4.5.3 "403 Forbidden"
612 The server understood the request, but is refusing to fulfill it.
613 Authorization will not help and the request SHOULD NOT be repeated.
615 4.5.4 "404 Not Found"
617 The server has not found anything matching the Request-URI. No indication
618 is given of whether the condition is temporary or permanent.
620 4.5.5 "405 Method Not Allowed"
622 The method specified in the Request-Line is not allowed for the resource
623 identified by the Request-URI. The response MUST include an Allow header
624 containing a list of valid methods for the requested resource.
626 4.5.6 "301 Moved Permanently"
628 If you get this return code and an HTML output similar to this:
630 <H1>Moved Permanently</H1> The document has moved <A
631 HREF="http://same_url_now_with_a_trailing_slash/">here</A>.
633 it might be because you request a directory URL but without the trailing
634 slash. Try the same operation again _with_ the trailing URL, or use the
635 -L/--location option to follow the redirection.
637 4.6 Can you tell me what error code 142 means?
639 All curl error codes are described at the end of the man page, in the
640 section called "EXIT CODES".
642 Error codes that are larger than the highest documented error code means
643 that curl has exited due to a crash. This is a serious error, and we
644 appreciate a detailed bug report from you that describes how we could go
645 ahead and repeat this!
647 4.7 How do I keep user names and passwords secret in Curl command lines?
649 This problem has two sides:
651 The first part is to avoid having clear-text passwords in the command line
652 so that they don't appear in 'ps' outputs and similar. That is easily
653 avoided by using the "-K" option to tell curl to read parameters from a file
654 or stdin to which you can pass the secret info. curl itself will also
655 attempt to "hide" the given password by blanking out the option - this
656 doesn't work on all platforms.
658 To keep the passwords in your account secret from the rest of the world is
659 not a task that curl addresses. You could of course encrypt them somehow to
660 at least hide them from being read by human eyes, but that is not what
661 anyone would call security.
663 Also note that regular HTTP (using Basic authentication) and FTP passwords
664 are sent in clear across the network. All it takes for anyone to fetch them
665 is to listen on the network. Eavesdropping is very easy. Use more secure
666 authentication methods (like Digest, Negotiate or even NTLM) or consider the
667 SSL-based alternatives HTTPS and FTPS.
671 It is not a bug if the behavior is documented. Read the docs first.
672 Especially check out the KNOWN_BUGS file, it may be a documented bug!
674 If it is a problem with a binary you've downloaded or a package for your
675 particular platform, try contacting the person who built the package/archive
678 If there is a bug, read the BUGS document first. Then report it as described
681 4.9 Curl can't authenticate to the server that requires NTLM?
683 This is supported in curl 7.10.6 or later. No earlier curl version knows
686 NTLM is a Microsoft proprietary protocol. Proprietary formats are evil. You
687 should not use such ones.
689 4.10 My HTTP request using HEAD, PUT or DELETE doesn't work!
691 Many web servers allow or demand that the administrator configures the
692 server properly for these requests to work on the web server.
694 Some servers seem to support HEAD only on certain kinds of URLs.
696 To fully grasp this, try the documentation for the particular server
697 software you're trying to interact with. This is not anything curl can do
700 4.11 Why does my HTTP range requests return the full document?
702 Because the range may not be supported by the server, or the server may
703 choose to ignore it and return the full document anyway.
705 4.12 Why do I get "certificate verify failed" ?
707 You invoke curl 7.10 or later to communicate on a https:// URL and get an
708 error back looking something similar to this:
710 curl: (35) SSL: error:14090086:SSL routines:
711 SSL3_GET_SERVER_CERTIFICATE:certificate verify failed
713 Then it means that curl couldn't verify that the server's certificate was
714 good. Curl verifies the certificate using the CA cert bundle that comes with
715 the curl installation.
717 To disable the verification (which makes it act like curl did before 7.10),
718 use -k. This does however enable man-in-the-middle attacks.
720 If you get this failure but are having a CA cert bundle installed and used,
721 the server's certificate is not signed by one of the CA's in the bundle. It
722 might for example be self-signed. You then correct this problem by obtaining
723 a valid CA cert for the server. Or again, decrease the security by disabling
726 Details are also in the SSLCERTS file in the release archives, found online
727 here: http://curl.haxx.se/docs/sslcerts.html
732 5.1 Is libcurl thread-safe?
736 We have written the libcurl code specificly adjusted for multi-threaded
737 programs. libcurl will use thread-safe functions instead of non-safe ones if
738 your system has such.
740 We would appreciate some kind of report or README file from those who have
741 used libcurl in a threaded environment.
743 5.2 How can I receive all data into a large memory chunk?
745 [ See also the examples/getinmemory.c source ]
747 You are in full control of the callback function that gets called every time
748 there is data received from the remote server. You can make that callback do
749 whatever you want. You do not have to write the received data to a file.
751 One solution to this problem could be to have a pointer to a struct that you
752 pass to the callback function. You set the pointer using the
753 curl_easy_setopt(CURLOPT_FILE) function. Then that pointer will be passed to
754 the callback instead of a FILE * to a file:
756 /* imaginary struct */
757 struct MemoryStruct {
762 /* imaginary callback function */
764 WriteMemoryCallback(void *ptr, size_t size, size_t nmemb, void *data)
766 size_t realsize = size * nmemb;
767 struct MemoryStruct *mem = (struct MemoryStruct *)data;
769 mem->memory = (char *)realloc(mem->memory, mem->size + realsize + 1);
771 memcpy(&(mem->memory[mem->size]), ptr, realsize);
772 mem->size += realsize;
773 mem->memory[mem->size] = 0;
778 5.3 How do I fetch multiple files with libcurl?
780 libcurl has excellent support for transferring multiple files. You should
781 just repeatedly set new URLs with curl_easy_setopt() and then transfer it
782 with curl_easy_perform(). The handle you get from curl_easy_init() is not
783 only reusable, but you're even encouraged to reuse it if you can, as that
784 will enable libcurl to use persistent connections.
786 5.4 Does libcurl do Winsock initialization on win32 systems?
788 Yes, if told to in the curl_global_init() call.
790 5.5 Does CURLOPT_WRITEDATA and CURLOPT_READDATA work on win32 ?
792 Yes, but you cannot open a FILE * and pass the pointer to a DLL and have
793 that DLL use the FILE * (as the DLL and the client application cannot access
794 each others' variable memory areas). If you set CURLOPT_WRITEDATA you must
795 also use CURLOPT_WRITEFUNCTION as well to set a function that writes the
796 file, even if that simply writes the data to the specified FILE *.
797 Similarly, if you use CURLOPT_READDATA you must also specify
798 CURLOPT_READFUNCTION.
800 (Provided by Joel DeYoung and Bob Schader)
802 5.6 What about Keep-Alive or persistent connections?
804 curl and libcurl have excellent support for persistent connections when
805 transferring several files from the same server. Curl will attempt to reuse
806 connections for all URLs specified on the same command line/config file, and
807 libcurl will reuse connections for all transfers that are made using the
810 5.7 Link errors when building libcurl on Windows!
812 You need to make sure that your project, and all the libraries (both static
813 and dynamic) that it links against, are compiled/linked against the same run
816 This is determined by the /MD, /ML, /MT (and their corresponding /M?d)
817 options to the command line compiler. /MD (linking against MSVCRT dll) seems
818 to be the most commonly used option.
820 (Provided by Andrew Francis)
822 When building an application that uses the static libcurl library, you must
823 add -DCURL_STATICLIB to your CFLAGS. Otherwise the linker will look for
824 dynamic import symbols. If you get linker error like "unknown symbol
825 __imp__curl_easy_init ..." you have linked against the wrong (static)
826 library. If you want to use the libcurl.dll and import lib, you don't need
827 any extra CFLAGS, but use one of the import libraries below. These are the
828 libraries produced by the various lib/Makefile.* files:
830 Target: static lib. import lib for libcurl*.dll.
831 -----------------------------------------------------------
832 MingW: libcurl.a libcurldll.a
833 MSVC (release): libcurl.lib libcurl_imp.lib
834 MSVC (debug): libcurld.lib libcurld_imp.lib
835 Borland: libcurl.lib libcurl_imp.lib
838 5.8 libcurl.so.3: open failed: No such file or directory
840 This is an error message you might get when you try to run a program linked
841 with a shared version of libcurl and your run-time linker (ld.so) couldn't
842 find the shared library named libcurl.so.3.
844 You need to make sure that ld.so finds libcurl.so.3. You can do that
845 multiple ways, and it differs somewhat between different operating systems,
846 but they are usually:
848 * Add an option to the linker command line that specify the hard-coded path
849 the run-time linker should check for the lib (usually -R)
851 * Set an environment variable (LD_LIBRARY_PATH for example) where ld.so
852 should check for libs
854 * Adjust the system's config to check for libs in the directory where you've
855 put the dir (like Linux's /etc/ld.so.conf)
857 'man ld.so' and 'man ld' will tell you more details
859 5.9 How does libcurl resolve host names?
861 libcurl includes a number of different name resolve functions:
863 - The non-ipv6 resolver that can use one out of four host name resolve calls
864 (depending on what your system supports):
867 B - gethostbyname_r() with 3 arguments
868 C - gethostbyname_r() with 5 arguments
869 D - gethostbyname_r() with 6 arguments
871 - The ipv6-resolver that uses getaddrinfo()
873 - The c-ares based name resolver that uses the c-ares library for resolves.
875 - The Windows threaded resolver. It use:
877 A - gethostbyname() on plain ipv4 windows hosts
878 B - getaddrinfo() on ipv6-enabled windows hosts
882 Curl and libcurl are released under a MIT/X derivate license. The license is
883 very liberal and should not impose a problem for your project. This section
884 is just a brief summary for the cases we get the most questions. (Parts of
885 this section was much enhanced by Bjorn Reese.)
887 6.1 I have a GPL program, can I use the libcurl library?
891 Since libcurl may be distributed under the MIT/X derivate license, it can be
892 used together with GPL in any software.
894 6.2 I have a closed-source program, can I use the libcurl library?
898 libcurl does not put any restrictions on the program that uses the library.
900 6.3 I have a BSD licensed program, can I use the libcurl library?
904 libcurl does not put any restrictions on the program that uses the library.
906 6.4 I have a program that uses LGPL libraries, can I use libcurl?
910 The LGPL license doesn't clash with other licenses.
912 6.5 Can I modify curl/libcurl for my program and keep the changes secret?
916 The MIT/X derivate license practically allows you to do almost anything with
917 the sources, on the condition that the copyright texts in the sources are
920 6.6 Can you please change the curl/libcurl license to XXXX?
924 We have carefully picked this license after years of development and
925 discussions and a large amount of people have contributed with source code
926 knowing that this is the license we use. This license puts the restrictions
927 we want on curl/libcurl and it does not spread to other programs or
928 libraries that use it. It should be possible for everyone to use libcurl or
929 curl in their projects, no matter what license they already have in use.
933 7.1 What is PHP/CURL?
935 The module for PHP that makes it possible for PHP programs to access curl-
936 functions from within PHP. We often call it PHP/CURL to differentiate from
937 curl the command line tool and libcurl the library.
939 7.2 Who write PHP/CURL?
941 PHP/CURL is a module that comes with the regular PHP package. It depends and
942 uses libcurl, so you need to have libcurl installed properly first before
943 PHP/CURL can be used. PHP/CURL is written by Sterling Hughes.
945 7.3 Can I perform multiple requests using the same handle?
947 Yes - at least in PHP version 4.3.8 and later (this has been known to not
948 work in earlier versions, but the exact version when it started to work is
951 After a transfer, you just set new options in the handle and make another
952 transfer. This will make libcurl to re-use the same connection if it can.