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CURLOPT_CAINFO(3) curl_easy_setopt options CURLOPT_CAINFO(3)


CURLOPT_CAINFO - path to Certificate Authority (CA) bundle


#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_CAINFO, char *path);


Pass a char * to a zero terminated string naming a file holding one or more certificates to verify the peer with.

If CURLOPT_SSL_VERIFYPEER(3) is zero and you avoid verifying the server's certificate, CURLOPT_CAINFO(3) need not even indicate an accessible file.

This option is by default set to the system path where libcurl's cacert bundle is assumed to be stored, as established at build time.

If curl is built against the NSS SSL library, the NSS PEM PKCS#11 module ( needs to be available for this option to work properly. Starting with curl-7.55.0, if both CURLOPT_CAINFO(3) and CURLOPT_CAPATH(3) are unset, NSS-linked libcurl tries to load, which contains a more comprehensive set of trust information than supported by nss-pem, because also includes information about distrusted certificates.

(iOS and macOS only) If curl is built against Secure Transport, then this option is supported for backward compatibility with other SSL engines, but it should not be set. If the option is not set, then curl will use the certificates in the system and user Keychain to verify the peer, which is the preferred method of verifying the peer's certificate chain.

(Schannel only) This option is supported for Schannel in Windows 7 or later with libcurl 7.60 or later. This option is supported for backward compatibility with other SSL engines; instead it is recommended to use Windows' store of root certificates (the default for Schannel).

The application does not have to keep the string around after setting this option.


Built-in system specific


All TLS based protocols: HTTPS, FTPS, IMAPS, POP3S, SMTPS etc.


CURL *curl = curl_easy_init();
if(curl) {
  curl_easy_setopt(curl, CURLOPT_URL, "");
  curl_easy_setopt(curl, CURLOPT_CAINFO, "/etc/certs/cabundle.pem");
  ret = curl_easy_perform(curl);


For SSL engines that don't support certificate files the CURLOPT_CAINFO option is ignored. Refer to


Returns CURLE_OK if the option is supported, CURLE_UNKNOWN_OPTION if not, or CURLE_OUT_OF_MEMORY if there was insufficient heap space.


January 29, 2019 libcurl 7.64.0