_ _ ____ _

___| | | | _ \| |

/ __| | | | |_) | |

| (__| |_| | _ <| |___

\___|\___/|_| \_\_____|

FAQ

1. Philosophy

1.1 What is cURL?

1.2 What is libcurl?

1.3 What is curl not?

1.4 When will you make curl do XXXX ?

1.5 Who makes curl?

1.6 What do you get for making curl?

1.7 What about CURL from curl.com?

1.8 I have a problem, who do I mail?

1.9 Where do I buy commercial support for curl?

1.10 How many are using curl?

1.11 Why do you not update ca-bundle.crt

1.12 I have a problem, who can I chat with?

1.13 curl's ECCN number?

1.14 How do I submit my patch?

1.15 How do I port libcurl to my OS?

2. Install Related Problems

2.1 configure fails when using static libraries

2.2 Does curl work/build with other SSL libraries?

2.3 How do I upgrade curl.exe in Windows?

2.4 Does curl support SOCKS (RFC 1928) ?

3. Usage Problems

3.1 curl: (1) SSL is disabled, https: not supported

3.2 How do I tell curl to resume a transfer?

3.3 Why does my posting using -F not work?

3.4 How do I tell curl to run custom FTP commands?

3.5 How can I disable the Accept: */* header?

3.6 Does curl support ASP, XML, XHTML or HTML version Y?

3.7 Can I use curl to delete/rename a file through FTP?

3.8 How do I tell curl to follow HTTP redirects?

3.9 How do I use curl in my favorite programming language?

3.10 What about SOAP, WebDAV, XML-RPC or similar protocols over HTTP?

3.11 How do I POST with a different Content-Type?

3.12 Why do FTP-specific features over HTTP proxy fail?

3.13 Why do my single/double quotes fail?

3.14 Does curl support JavaScript or PAC (automated proxy config)?

3.15 Can I do recursive fetches with curl?

3.16 What certificates do I need when I use SSL?

3.17 How do I list the root directory of an FTP server?

3.18 Can I use curl to send a POST/PUT and not wait for a response?

3.19 How do I get HTTP from a host using a specific IP address?

3.20 How to SFTP from my user's home directory?

3.21 Protocol xxx not supported or disabled in libcurl

3.22 curl -X gives me HTTP problems

4. Running Problems

4.2 Why do I get problems when I use & or % in the URL?

4.3 How can I use {, }, [ or ] to specify multiple URLs?

4.4 Why do I get downloaded data even though the webpage does not exist?

4.5 Why do I get return code XXX from an HTTP server?

4.5.1 "400 Bad Request"

4.5.2 "401 Unauthorized"

4.5.3 "403 Forbidden"

4.5.4 "404 Not Found"

4.5.5 "405 Method Not Allowed"

4.5.6 "301 Moved Permanently"

4.6 Can you tell me what error code 142 means?

4.7 How do I keep usernames and passwords secret in curl command lines?

4.8 I found a bug

4.9 curl cannot authenticate to a server that requires NTLM?

4.10 My HTTP request using HEAD, PUT or DELETE does not work

4.11 Why do my HTTP range requests return the full document?

4.12 Why do I get "certificate verify failed" ?

4.13 Why is curl -R on Windows one hour off?

4.14 Redirects work in browser but not with curl

4.15 FTPS does not work

4.16 My HTTP POST or PUT requests are slow

4.17 Non-functional connect timeouts on Windows

4.18 file:// URLs containing drive letters (Windows, NetWare)

4.19 Why does not curl return an error when the network cable is unplugged?

4.20 curl does not return error for HTTP non-200 responses

5. libcurl Issues

5.1 Is libcurl thread-safe?

5.2 How can I receive all data into a large memory chunk?

5.3 How do I fetch multiple files with libcurl?

5.4 Does libcurl do Winsock initialization on Win32 systems?

5.5 Does CURLOPT_WRITEDATA and CURLOPT_READDATA work on Win32 ?

5.6 What about Keep-Alive or persistent connections?

5.7 Link errors when building libcurl on Windows

5.8 libcurl.so.X: open failed: No such file or directory

5.9 How does libcurl resolve hostnames?

5.10 How do I prevent libcurl from writing the response to stdout?

5.11 How do I make libcurl not receive the whole HTTP response?

5.12 Can I make libcurl fake or hide my real IP address?

5.13 How do I stop an ongoing transfer?

5.14 Using C++ non-static functions for callbacks?

5.15 How do I get an FTP directory listing?

5.16 I want a different time-out

5.17 Can I write a server with libcurl?

5.18 Does libcurl use threads?

6. License Issues

6.1 I have a GPL program, can I use the libcurl library?

6.2 I have a closed-source program, can I use the libcurl library?

6.3 I have a BSD licensed program, can I use the libcurl library?

6.4 I have a program that uses LGPL libraries, can I use libcurl?

6.5 Can I modify curl/libcurl for my program and keep the changes secret?

6.6 Can you please change the curl/libcurl license to XXXX?

6.7 What are my obligations when using libcurl in my commercial apps?

7. PHP/CURL Issues

7.1 What is PHP/CURL?

7.2 Who wrote PHP/CURL?

7.3 Can I perform multiple requests using the same handle?

7.4 Does PHP/CURL have dependencies?

8. Development

8.1 Why does curl use C89?

8.2 Will curl be rewritten?

==============================================================================

1. Philosophy

1.1 What is cURL?

cURL is the name of the project. The name is a play on 'Client for URLs',

originally with URL spelled in uppercase to make it obvious it deals with

URLs. The fact it can also be read as 'see URL' also helped, it works as

an abbreviation for "Client URL Request Library" or why not the recursive

version: "curl URL Request Library".

The cURL project produces two products:

libcurl

A client-side URL transfer library, supporting DICT, FILE, FTP, FTPS,

GOPHER, GOPHERS, HTTP, HTTPS, IMAP, IMAPS, LDAP, LDAPS, MQTT, POP3, POP3S,

RTMP, RTMPS, RTSP, SCP, SFTP, SMB, SMBS, SMTP, SMTPS, TELNET, TFTP, WS

and WSS.

libcurl supports HTTPS certificates, HTTP POST, HTTP PUT, FTP uploading,

Kerberos, SPNEGO, HTTP form based upload, proxies, cookies, user+password

authentication, file transfer resume, http proxy tunneling and more.

libcurl is highly portable, it builds and works identically on numerous

platforms, including Solaris, NetBSD, FreeBSD, OpenBSD, Darwin, HP-UX,

IRIX, AIX, Tru64, Linux, UnixWare, HURD, Windows, Amiga, OS/2, macOS,

Ultrix, QNX, OpenVMS, RISC OS, Novell NetWare, DOS, Symbian, OSF, Android,

Minix, IBM TPF and more...

libcurl is free, thread-safe, IPv6 compatible, feature rich, well

supported and fast.

curl

A command line tool for getting or sending data using URL syntax.

Since curl uses libcurl, curl supports the same wide range of common

Internet protocols that libcurl does.

We pronounce curl with an initial k sound. It rhymes with words like girl

and earl. This is a short WAV file to help you:

https://media.merriam-webster.com/soundc11/c/curl0001.wav

There are numerous sub-projects and related projects that also use the word

curl in the project names in various combinations, but you should take

notice that this FAQ is directed at the command-line tool named curl (and

libcurl the library), and may therefore not be valid for other curl-related

projects. (There is however a small section for the PHP/CURL in this FAQ.)

1.2 What is libcurl?

libcurl is a reliable and portable library for doing Internet data transfers

using one or more of its supported Internet protocols.

You can use libcurl freely in your application, be it open source,

commercial or closed-source.

libcurl is most probably the most portable, most powerful and most often

used C-based multi-platform file transfer library on this planet - be it

open source or commercial.

1.3 What is curl not?

curl is not a wget clone. That is a common misconception. Never, during

curl's development, have we intended curl to replace wget or compete on its

market. curl is targeted at single-shot file transfers.

curl is not a website mirroring program. If you want to use curl to mirror

something: fine, go ahead and write a script that wraps around curl or use

libcurl to make it reality.

curl is not an FTP site mirroring program. Sure, get and send FTP with curl

but if you want systematic and sequential behavior you should write a

script (or write a new program that interfaces libcurl) and do it.

curl is not a PHP tool, even though it works perfectly well when used from

or with PHP (when using the PHP/CURL module).

curl is not a program for a single operating system. curl exists, compiles,

builds and runs under a wide range of operating systems, including all

modern Unixes (and a bunch of older ones too), Windows, Amiga, OS/2, macOS,

QNX etc.

1.4 When will you make curl do XXXX ?

We love suggestions of what to change in order to make curl and libcurl

better. We do however believe in a few rules when it comes to the future of

curl:

curl -- the command line tool -- is to remain a non-graphical command line

tool. If you want GUIs or fancy scripting capabilities, you should look for

another tool that uses libcurl.

We do not add things to curl that other small and available tools already do

well at the side. curl's output can be piped into another program or

redirected to another file for the next program to interpret.

We focus on protocol related issues and improvements. If you want to do more

magic with the supported protocols than curl currently does, chances are

good we will agree. If you want to add more protocols, we may agree.

If you want someone else to do all the work while you wait for us to

implement it for you, that is not a friendly attitude. We spend a

considerable time already on maintaining and developing curl. In order to

get more out of us, you should consider trading in some of your time and

effort in return. Simply go to the GitHub repository which resides at

https://github.com/curl/curl, fork the project, and create pull requests

with your proposed changes.

If you write the code, chances are better that it will get into curl faster.

1.5 Who makes curl?

curl and libcurl are not made by any single individual. Daniel Stenberg is

project leader and main developer, but other persons' submissions are

important and crucial. Anyone can contribute and post their changes and

improvements and have them inserted in the main sources (of course on the

condition that developers agree that the fixes are good).

The full list of all contributors is found in the docs/THANKS file.

curl is developed by a community, with Daniel at the wheel.

1.6 What do you get for making curl?

Project cURL is entirely free and open. We do this voluntarily, mostly in

our spare time. Companies may pay individual developers to work on curl.

This is not controlled by nor supervised in any way by the curl project.

We get help from companies. Haxx provides website, bandwidth, mailing lists

etc, GitHub hosts the primary git repository and other services like the bug

tracker at https://github.com/curl/curl. Also again, some companies have

sponsored certain parts of the development in the past and I hope some will

continue to do so in the future.

If you want to support our project, consider a donation or a banner-program

or even better: by helping us with coding, documenting or testing etc.

See also: https://curl.se/sponsors.html

1.7 What about CURL from curl.com?

During the summer of 2001, curl.com was busy advertising their client-side

programming language for the web, named CURL.

We are in no way associated with curl.com or their CURL programming

language.

Our project name curl has been in effective use since 1998. We were not the

first computer related project to use the name "curl" and do not claim any

rights to the name.

We recognize that we will be living in parallel with curl.com and wish them

every success.

1.8 I have a problem, who do I mail?

Please do not mail any single individual unless you really need to. Keep

curl-related questions on a suitable mailing list. All available mailing

lists are listed in the MANUAL document and online at

https://curl.se/mail/

Keeping curl-related questions and discussions on mailing lists allows

others to join in and help, to share their ideas, to contribute their

suggestions and to spread their wisdom. Keeping discussions on public mailing

lists also allows for others to learn from this (both current and future

users thanks to the web based archives of the mailing lists), thus saving us

from having to repeat ourselves even more. Thanks for respecting this.

If you have found or simply suspect a security problem in curl or libcurl,

submit all the details at https://hackerone.one/curl. On there we keep the

issue private while we investigate, confirm it, work and validate a fix and

agree on a time schedule for publication etc. That way we produce a fix in a

timely manner before the flaw is announced to the world, reducing the impact

the problem risks having on existing users.

Security issues can also be taking to the curl security team by emailing

security at curl.se (closed list of receivers, mails are not disclosed).

1.9 Where do I buy commercial support for curl?

curl is fully open source. It means you can hire any skilled engineer to fix

your curl-related problems.

We list available alternatives on the curl website:

https://curl.se/support.html

1.10 How many are using curl?

It is impossible to tell.

We do not know how many users that knowingly have installed and use curl.

We do not know how many users that use curl without knowing that they are in

fact using it.

We do not know how many users that downloaded or installed curl and then

never use it.

In 2020, we estimate that curl runs in roughly ten billion installations

world wide.

1.11 Why do you not update ca-bundle.crt

In the cURL project we have decided not to attempt to keep this file updated

(or even present) since deciding what to add to a ca cert bundle is an

undertaking we have not been ready to accept, and the one we can get from

Mozilla is perfectly fine so there is no need to duplicate that work.

Today, with many services performed over HTTPS, every operating system

should come with a default ca cert bundle that can be deemed somewhat

trustworthy and that collection (if reasonably updated) should be deemed to

be a lot better than a private curl version.

If you want the most recent collection of ca certs that Mozilla Firefox

uses, we recommend that you extract the collection yourself from Mozilla

Firefox (by running 'make ca-bundle), or by using our online service setup

for this purpose: https://curl.se/docs/caextract.html

1.12 I have a problem who, can I chat with?

There is a bunch of friendly people hanging out in the #curl channel on the

IRC network libera.chat. If you are polite and nice, chances are good that

you can get -- or provide -- help instantly.

1.13 curl's ECCN number?

The US government restricts exports of software that contains or uses

cryptography. When doing so, the Export Control Classification Number (ECCN)

is used to identify the level of export control etc.

Apache Software Foundation gives a good explanation of ECCNs at

https://www.apache.org/dev/crypto.html

We believe curl's number might be ECCN 5D002, another possibility is

5D992. It seems necessary to write them (the authority that administers ECCN

numbers), asking to confirm.

Comprehensible explanations of the meaning of such numbers and how to obtain

them (resp.) are here

https://www.bis.doc.gov/licensing/exportingbasics.htm

https://www.bis.doc.gov/licensing/do_i_needaneccn.html

An incomprehensible description of the two numbers above is here

https://www.bis.doc.gov/index.php/documents/new-encryption/1653-ccl5-pt2-3

1.14 How do I submit my patch?

We strongly encourage you to submit changes and improvements directly as

"pull requests" on GitHub: https://github.com/curl/curl/pulls

If you for any reason cannot or will not deal with GitHub, send your patch to

the curl-library mailing list. We are many subscribers there and there are

lots of people who can review patches, comment on them and "receive" them

properly.

Lots of more details are found in the CONTRIBUTE.md and INTERNALS.md

documents.

1.15 How do I port libcurl to my OS?

Here's a rough step-by-step:

1. copy a suitable lib/config-*.h file as a start to lib/config-[youros].h

2. edit lib/config-[youros].h to match your OS and setup

3. edit lib/curl_setup.h to include config-[youros].h when your OS is

detected by the preprocessor, in the style others already exist

4. compile lib/*.c and make them into a library

2. Install Related Problems

2.1 configure fails when using static libraries

You may find that configure fails to properly detect the entire dependency

chain of libraries when you provide static versions of the libraries that

configure checks for.

The reason why static libraries is much harder to deal with is that for them

we do not get any help but the script itself must know or check what more

libraries that are needed (with shared libraries, that dependency "chain" is

handled automatically). This is an error-prone process and one that also

tends to vary over time depending on the release versions of the involved

components and may also differ between operating systems.

For that reason, configure does few attempts to actually figure this out and

you are instead encouraged to set LIBS and LDFLAGS accordingly when you

invoke configure, and point out the needed libraries and set the necessary

flags yourself.

2.2 Does curl work with other SSL libraries?

curl has been written to use a generic SSL function layer internally, and

that SSL functionality can then be provided by one out of many different SSL

backends.

curl can be built to use one of the following SSL alternatives: OpenSSL,

LibreSSL, BoringSSL, AWS-LC, GnuTLS, wolfSSL, mbedTLS, Secure Transport

(native iOS/macOS), Schannel (native Windows), BearSSL or Rustls. They all

have their pros and cons, and we try to maintain a comparison of them here:

https://curl.se/docs/ssl-compared.html

2.3 How do I upgrade curl.exe in Windows?

The curl tool that is shipped as an integrated component of Windows 10 and

Windows 11 is managed by Microsoft. If you were to delete the file or

replace it with a newer version downloaded from https://curl.se/windows,

then Windows Update will cease to work on your system.

There is no way to independently force an upgrade of the curl.exe that is

part of Windows other than through the regular Windows update process. There

is also nothing the curl project itself can do about this, since this is

managed and controlled entirely by Microsoft as owners of the operating

system.

You can always download and install the latest version of curl for Windows

from https://curl.se/windows into a separate location.

2.4 Does curl support SOCKS (RFC 1928) ?

Yes, SOCKS 4 and 5 are supported.

3. Usage problems

3.1 curl: (1) SSL is disabled, https: not supported

If you get this output when trying to get anything from an HTTPS server, it

means that the instance of curl/libcurl that you are using was built without

support for this protocol.

This could have happened if the configure script that was run at build time

could not find all libs and include files curl requires for SSL to work. If

the configure script fails to find them, curl is simply built without SSL

support.

To get HTTPS support into a curl that was previously built but that reports

that HTTPS is not supported, you should dig through the document and logs

and check out why the configure script does not find the SSL libs and/or

include files.

Also, check out the other paragraph in this FAQ labeled "configure does not

find OpenSSL even when it is installed".

3.2 How do I tell curl to resume a transfer?

curl supports resumed transfers both ways on both FTP and HTTP.

Try the -C option.

3.3 Why does my posting using -F not work?

You cannot arbitrarily use -F or -d, the choice between -F or -d depends on

the HTTP operation you need curl to do and what the web server that will

receive your post expects.

If the form you are trying to submit uses the type 'multipart/form-data',

then and only then you must use the -F type. In all the most common cases,

you should use -d which then causes a posting with the type

'application/x-www-form-urlencoded'.

This is described in some detail in the MANUAL and TheArtOfHttpScripting

documents, and if you do not understand it the first time, read it again

before you post questions about this to the mailing list. Also, try reading

through the mailing list archives for old postings and questions regarding

this.

3.4 How do I tell curl to run custom FTP commands?

You can tell curl to perform optional commands both before and/or after a

file transfer. Study the -Q/--quote option.

Since curl is used for file transfers, you do not normally use curl to

perform FTP commands without transferring anything. Therefore you must

always specify a URL to transfer to/from even when doing custom FTP

commands, or use -I which implies the "no body" option sent to libcurl.

3.5 How can I disable the Accept: */* header?

You can change all internally generated headers by adding a replacement with

the -H/--header option. By adding a header with empty contents you safely

disable that one. Use -H "Accept:" to disable that specific header.

3.6 Does curl support ASP, XML, XHTML or HTML version Y?

To curl, all contents are alike. It does not matter how the page was

generated. It may be ASP, PHP, Perl, shell-script, SSI or plain HTML

files. There is no difference to curl and it does not even know what kind of

language that generated the page.

See also item 3.14 regarding JavaScript.

3.7 Can I use curl to delete/rename a file through FTP?

Yes. You specify custom FTP commands with -Q/--quote.

One example would be to delete a file after you have downloaded it:

curl -O ftp://example.com/coolfile -Q '-DELE coolfile'

or rename a file after upload:

curl -T infile ftp://example.com/dir/ -Q "-RNFR infile" -Q "-RNTO newname"

3.8 How do I tell curl to follow HTTP redirects?

curl does not follow so-called redirects by default. The Location: header

that informs the client about this is only interpreted if you are using the

-L/--location option. As in:

curl -L http://example.com

Not all redirects are HTTP ones, see 4.14

3.9 How do I use curl in my favorite programming language?

Many programming languages have interfaces/bindings that allow you to use

curl without having to use the command line tool. If you are fluent in such

a language, you may prefer to use one of these interfaces instead.

Find out more about which languages that support curl directly, and how to

install and use them, in the libcurl section of the curl website:

https://curl.se/libcurl/

All the various bindings to libcurl are made by other projects and people,

outside of the cURL project. The cURL project itself only produces libcurl

with its plain C API. If you do not find anywhere else to ask you can ask

about bindings on the curl-library list too, but be prepared that people on

that list may not know anything about bindings.

In December 2021, there were interfaces available for the following

languages: Ada95, Basic, C, C++, Ch, Cocoa, D, Delphi, Dylan, Eiffel,

Euphoria, Falcon, Ferite, Gambas, glib/GTK+, Go, Guile, Harbour, Haskell,

Java, Julia, Lisp, Lua, Mono, .NET, node.js, Object-Pascal, OCaml, Pascal,

Perl, PHP, PostgreSQL, Python, R, Rexx, Ring, RPG, Ruby, Rust, Scheme,

Scilab, S-Lang, Smalltalk, SP-Forth, SPL, Tcl, Visual Basic, Visual FoxPro,

Q, wxwidgets, XBLite and Xoho. By the time you read this, additional ones

may have appeared.

3.10 What about SOAP, WebDAV, XML-RPC or similar protocols over HTTP?

curl adheres to the HTTP spec, which basically means you can play with *any*

protocol that is built on top of HTTP. Protocols such as SOAP, WebDAV and

XML-RPC are all such ones. You can use -X to set custom requests and -H to

set custom headers (or replace internally generated ones).

Using libcurl is of course just as good and you would just use the proper

library options to do the same.

3.11 How do I POST with a different Content-Type?

You can always replace the internally generated headers with -H/--header.

To make a simple HTTP POST with text/xml as content-type, do something like:

curl -d "datatopost" -H "Content-Type: text/xml" [URL]

3.12 Why do FTP-specific features over HTTP proxy fail?

Because when you use an HTTP proxy, the protocol spoken on the network will

be HTTP, even if you specify an FTP URL. This effectively means that you

normally cannot use FTP-specific features such as FTP upload and FTP quote

etc.

There is one exception to this rule, and that is if you can "tunnel through"

the given HTTP proxy. Proxy tunneling is enabled with a special option (-p)

and is generally not available as proxy admins usually disable tunneling to

ports other than 443 (which is used for HTTPS access through proxies).

3.13 Why do my single/double quotes fail?

To specify a command line option that includes spaces, you might need to

put the entire option within quotes. Like in:

curl -d " with spaces " example.com

or perhaps

curl -d ' with spaces ' example.com

Exactly what kind of quotes and how to do this is entirely up to the shell

or command line interpreter that you are using. For most Unix shells, you

can more or less pick either single (') or double (") quotes. For

Windows/DOS command prompts you must use double (") quotes, and if the

option string contains inner double quotes you can escape them with a

backslash.

For Windows powershell the arguments are not always passed on as expected

because curl is not a powershell script. You may or may not be able to use

single quotes. To escape inner double quotes seems to require a

backslash-backtick escape sequence and the outer quotes as double quotes.

Please study the documentation for your particular environment. Examples in

the curl docs will use a mix of both of these as shown above. You must

adjust them to work in your environment.

Remember that curl works and runs on more operating systems than most single

individuals have ever tried.

3.14 Does curl support JavaScript or PAC (automated proxy config)?

Many webpages do magic stuff using embedded JavaScript. curl and libcurl

have no built-in support for that, so it will be treated just like any other

contents.

.pac files are a Netscape invention and are sometimes used by organizations

to allow them to differentiate which proxies to use. The .pac contents is

just a JavaScript program that gets invoked by the browser and that returns

the name of the proxy to connect to. Since curl does not support JavaScript,

it cannot support .pac proxy configuration either.

Some workarounds usually suggested to overcome this JavaScript dependency:

Depending on the JavaScript complexity, write up a script that translates it

to another language and execute that.

Read the JavaScript code and rewrite the same logic in another language.

Implement a JavaScript interpreter, people have successfully used the

Mozilla JavaScript engine in the past.

Ask your admins to stop this, for a static proxy setup or similar.

3.15 Can I do recursive fetches with curl?

No. curl itself has no code that performs recursive operations, such as

those performed by wget and similar tools.

There exists wrapper scripts with that functionality (for example the

curlmirror perl script), and you can write programs based on libcurl to do

it, but the command line tool curl itself cannot.

3.16 What certificates do I need when I use SSL?

There are three different kinds of "certificates" to keep track of when we

talk about using SSL-based protocols (HTTPS or FTPS) using curl or libcurl.

CLIENT CERTIFICATE

The server you communicate with may require that you can provide this in

order to prove that you actually are who you claim to be. If the server

does not require this, you do not need a client certificate.

A client certificate is always used together with a private key, and the

private key has a pass phrase that protects it.

SERVER CERTIFICATE

The server you communicate with has a server certificate. You can and should

verify this certificate to make sure that you are truly talking to the real

server and not a server impersonating it.

CERTIFICATE AUTHORITY CERTIFICATE ("CA cert")

You often have several CA certs in a CA cert bundle that can be used to

verify a server certificate that was signed by one of the authorities in the

bundle. curl does not come with a CA cert bundle but most curl installs

provide one. You can also override the default.

The server certificate verification process is made by using a Certificate

Authority certificate ("CA cert") that was used to sign the server

certificate. Server certificate verification is enabled by default in curl

and libcurl and is often the reason for problems as explained in FAQ entry

4.12 and the SSLCERTS document

(https://curl.se/docs/sslcerts.html). Server certificates that are

"self-signed" or otherwise signed by a CA that you do not have a CA cert

for, cannot be verified. If the verification during a connect fails, you are

refused access. You then need to explicitly disable the verification to

connect to the server.

3.17 How do I list the root directory of an FTP server?

There are two ways. The way defined in the RFC is to use an encoded slash

in the first path part. List the "/tmp" directory like this:

curl ftp://ftp.example.com/%2ftmp/

or the not-quite-kosher-but-more-readable way, by simply starting the path

section of the URL with a slash:

curl ftp://ftp.example.com//tmp/

3.18 Can I use curl to send a POST/PUT and not wait for a response?

No.

You can easily write your own program using libcurl to do such stunts.

3.19 How do I get HTTP from a host using a specific IP address?

For example, you may be trying out a website installation that is not yet in

the DNS. Or you have a site using multiple IP addresses for a given host

name and you want to address a specific one out of the set.

Set a custom Host: header that identifies the server name you want to reach

but use the target IP address in the URL:

curl --header "Host: www.example.com" http://127.0.0.1/

You can also opt to add faked hostname entries to curl with the --resolve

option. That has the added benefit that things like redirects will also work

properly. The above operation would instead be done as:

curl --resolve www.example.com:80:127.0.0.1 http://www.example.com/

3.20 How to SFTP from my user's home directory?

Contrary to how FTP works, SFTP and SCP URLs specify the exact directory to

work with. It means that if you do not specify that you want the user's home

directory, you get the actual root directory.

To specify a file in your user's home directory, you need to use the correct

URL syntax which for SFTP might look similar to:

curl -O -u user:password sftp://example.com/~/file.txt

and for SCP it is just a different protocol prefix:

curl -O -u user:password scp://example.com/~/file.txt

3.21 Protocol xxx not supported or disabled in libcurl

When passing on a URL to curl to use, it may respond that the particular

protocol is not supported or disabled. The particular way this error message

is phrased is because curl does not make a distinction internally of whether

a particular protocol is not supported (i.e. never got any code added that

knows how to speak that protocol) or if it was explicitly disabled. curl can

be built to only support a given set of protocols, and the rest would then

be disabled or not supported.

Note that this error will also occur if you pass a wrongly spelled protocol

part as in "htpt://example.com" or as in the less evident case if you prefix

the protocol part with a space as in " http://example.com/".

3.22 curl -X gives me HTTP problems

In normal circumstances, -X should hardly ever be used.

By default you use curl without explicitly saying which request method to

use when the URL identifies an HTTP transfer. If you just pass in a URL like

"curl http://example.com" it will use GET. If you use -d or -F curl will use

POST, -I will cause a HEAD and -T will make it a PUT.

If for whatever reason you are not happy with these default choices that curl

does for you, you can override those request methods by specifying -X

[WHATEVER]. This way you can for example send a DELETE by doing "curl -X

DELETE [URL]".

It is thus pointless to do "curl -XGET [URL]" as GET would be used anyway.

In the same vein it is pointless to do "curl -X POST -d data [URL]". You can

make a fun and somewhat rare request that sends a request-body in a GET

request with something like "curl -X GET -d data [URL]"

Note that -X does not actually change curl's behavior as it only modifies the

actual string sent in the request, but that may of course trigger a

different set of events.

Accordingly, by using -XPOST on a command line that for example would follow

a 303 redirect, you will effectively prevent curl from behaving

correctly. Be aware.

4. Running Problems

4.2 Why do I get problems when I use & or % in the URL?

In general Unix shells, the & symbol is treated specially and when used, it

runs the specified command in the background. To safely send the & as a part

of a URL, you should quote the entire URL by using single (') or double (")

quotes around it. Similar problems can also occur on some shells with other

characters, including ?*!$~(){}<>\|;`. When in doubt, quote the URL.

An example that would invoke a remote CGI that uses &-symbols could be:

curl 'http://www.example.com/cgi-bin/query?text=yes&q=curl'

In Windows, the standard DOS shell treats the percent sign specially and you

need to use TWO percent signs for each single one you want to use in the

URL.

If you want a literal percent sign to be part of the data you pass in a POST

using -d/--data you must encode it as '%25' (which then also needs the

percent sign doubled on Windows machines).

4.3 How can I use {, }, [ or ] to specify multiple URLs?

Because those letters have a special meaning to the shell, to be used in

a URL specified to curl you must quote them.

An example that downloads two URLs (sequentially) would be:

curl '{curl,www}.haxx.se'

To be able to use those characters as actual parts of the URL (without using

them for the curl URL "globbing" system), use the -g/--globoff option:

curl -g 'www.example.com/weirdname[].html'

4.4 Why do I get downloaded data even though the webpage does not exist?

curl asks remote servers for the page you specify. If the page does not exist

at the server, the HTTP protocol defines how the server should respond and

that means that headers and a "page" will be returned. That is simply how

HTTP works.

By using the --fail option you can tell curl explicitly to not get any data

if the HTTP return code does not say success.

4.5 Why do I get return code XXX from an HTTP server?

RFC 2616 clearly explains the return codes. This is a short transcript. Go

read the RFC for exact details:

4.5.1 "400 Bad Request"

The request could not be understood by the server due to malformed

syntax. The client SHOULD NOT repeat the request without modifications.

4.5.2 "401 Unauthorized"

The request requires user authentication.

4.5.3 "403 Forbidden"

The server understood the request, but is refusing to fulfill it.

Authorization will not help and the request SHOULD NOT be repeated.

4.5.4 "404 Not Found"

The server has not found anything matching the Request-URI. No indication

is given as to whether the condition is temporary or permanent.

4.5.5 "405 Method Not Allowed"

The method specified in the Request-Line is not allowed for the resource

identified by the Request-URI. The response MUST include an Allow header

containing a list of valid methods for the requested resource.

4.5.6 "301 Moved Permanently"

If you get this return code and an HTML output similar to this:

<H1>Moved Permanently</H1> The document has moved <A

HREF="http://same_url_now_with_a_trailing_slash/">here</A>.

it might be because you requested a directory URL but without the trailing

slash. Try the same operation again _with_ the trailing URL, or use the

-L/--location option to follow the redirection.

4.6 Can you tell me what error code 142 means?

All curl error codes are described at the end of the man page, in the

section called "EXIT CODES".

Error codes that are larger than the highest documented error code means

that curl has exited due to a crash. This is a serious error, and we

appreciate a detailed bug report from you that describes how we could go

ahead and repeat this.

4.7 How do I keep usernames and passwords secret in curl command lines?

This problem has two sides:

The first part is to avoid having clear-text passwords in the command line

so that they do not appear in 'ps' outputs and similar. That is easily

avoided by using the "-K" option to tell curl to read parameters from a file

or stdin to which you can pass the secret info. curl itself will also

attempt to "hide" the given password by blanking out the option - this

does not work on all platforms.

To keep the passwords in your account secret from the rest of the world is

not a task that curl addresses. You could of course encrypt them somehow to

at least hide them from being read by human eyes, but that is not what

anyone would call security.

Also note that regular HTTP (using Basic authentication) and FTP passwords

are sent as cleartext across the network. All it takes for anyone to fetch

them is to listen on the network. Eavesdropping is easy. Use more secure

authentication methods (like Digest, Negotiate or even NTLM) or consider the

SSL-based alternatives HTTPS and FTPS.

4.8 I found a bug

It is not a bug if the behavior is documented. Read the docs first.

Especially check out the KNOWN_BUGS file, it may be a documented bug.

If it is a problem with a binary you have downloaded or a package for your

particular platform, try contacting the person who built the package/archive

you have.

If there is a bug, read the BUGS document first. Then report it as described

in there.

4.9 curl cannot authenticate to a server that requires NTLM?

NTLM support requires OpenSSL, GnuTLS, mbedTLS, Secure Transport, or

Microsoft Windows libraries at build-time to provide this functionality.

4.10 My HTTP request using HEAD, PUT or DELETE does not work

Many web servers allow or demand that the administrator configures the

server properly for these requests to work on the web server.

Some servers seem to support HEAD only on certain kinds of URLs.

To fully grasp this, try the documentation for the particular server

software you are trying to interact with. This is not anything curl can do

anything about.

4.11 Why do my HTTP range requests return the full document?

Because the range may not be supported by the server, or the server may

choose to ignore it and return the full document anyway.

4.12 Why do I get "certificate verify failed" ?

When you invoke curl and get an error 60 error back it means that curl

could not verify that the server's certificate was good. curl verifies the

certificate using the CA cert bundle and verifying for which names the

certificate has been granted.

To completely disable the certificate verification, use -k. This does

however enable man-in-the-middle attacks and makes the transfer INSECURE.

We strongly advise against doing this for more than experiments.

If you get this failure with a CA cert bundle installed and used, the

server's certificate might not be signed by one of the CA's in your CA

store. It might for example be self-signed. You then correct this problem by

obtaining a valid CA cert for the server. Or again, decrease the security by

disabling this check.

At times, you find that the verification works in your favorite browser but

fails in curl. When this happens, the reason is usually that the server

sends an incomplete cert chain. The server is mandated to send all

"intermediate certificates" but does not. This typically works with browsers

anyway since they A) cache such certs and B) supports AIA which downloads

such missing certificates on demand. This is a server misconfiguration. A

good way to figure out if this is the case it to use the SSL Labs server

test and check the certificate chain: https://www.ssllabs.com/ssltest/

Details are also in the SSLCERTS.md document, found online here:

https://curl.se/docs/sslcerts.html

4.13 Why is curl -R on Windows one hour off?

Since curl 7.53.0 this issue should be fixed as long as curl was built with

any modern compiler that allows for a 64-bit curl_off_t type. For older

compilers or prior curl versions it may set a time that appears one hour off.

This happens due to a flaw in how Windows stores and uses file modification

times and it is not easily worked around. For more details read this:

https://www.codeproject.com/Articles/1144/Beating-the-Daylight-Savings-Time-bug-and-getting

4.14 Redirects work in browser but not with curl

curl supports HTTP redirects well (see item 3.8). Browsers generally support

at least two other ways to perform redirects that curl does not:

Meta tags. You can write an HTML tag that will cause the browser to redirect

to another given URL after a certain time.

JavaScript. You can write a JavaScript program embedded in an HTML page that

redirects the browser to another given URL.

There is no way to make curl follow these redirects. You must either

manually figure out what the page is set to do, or write a script that parses

the results and fetches the new URL.

4.15 FTPS does not work

curl supports FTPS (sometimes known as FTP-SSL) both implicit and explicit

mode.

When a URL is used that starts with FTPS://, curl assumes implicit SSL on

the control connection and will therefore immediately connect and try to

speak SSL. FTPS:// connections default to port 990.