CURLOPT_USE_SSL(3) Introduction to Library Functions CURLOPT_USE_SSL(3)
CURLOPT_USE_SSL - request using SSL / TLS for the transfer
#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_USE_SSL, long level);
Pass a long using one of the values from below, to make libcurl use
your desired level of SSL for the transfer.
These are all protocols that start out plain text and get "upgraded"
to SSL using the STARTTLS command.
This is for enabling SSL/TLS when you use FTP, SMTP, POP3, IMAP etc.
CURLUSESSL_NONE
Do not attempt to use SSL.
CURLUSESSL_TRY
Try using SSL, proceed as normal otherwise. Note that server
may close the connection if the negotiation fails. This level
is insecure and should be avoided since it allows the
connection to remain unprotected.
CURLUSESSL_CONTROL
Require SSL for the control connection or fail with
CURLE_USE_SSL_FAILED. This level is partially insecure and
should be avoided since it lets the data connection remain
unprotected.
This level is meant for FTP, since that is the only protocol
with separate connections for control and data. If used for
IMAP, POP3 or SMTP it equals CURLUSESSL_ALL.
CURLUSESSL_ALL
Require SSL for all communication or fail with
CURLE_USE_SSL_FAILED.
CURLUSESSL_NONE
This functionality affects ftp, imap, pop3 and smtp
int main(void)
{
CURL *curl = curl_easy_init();
if(curl) {
CURLcode result;
curl_easy_setopt(curl, CURLOPT_URL, "ftp://example.com/dir/file.ext");
/* require use of SSL for this, or fail */
curl_easy_setopt(curl, CURLOPT_USE_SSL, CURLUSESSL_ALL);
/* Perform the request */
result = curl_easy_perform(curl);
curl_easy_cleanup(curl);
}
}
This option was known as CURLOPT_FTP_SSL up to 7.16.4. Supported by
LDAP since 7.81.0. Fully supported by the OpenLDAP backend only.
CURLUSESSL_* enums became long types in 8.13.0, prior to this version
a long cast was necessary when passed to curl_easy_setopt(3).
Added in curl 7.17.0
curl_easy_setopt(3) returns a CURLcode indicating success or error.
CURLE_OK (0) means everything was OK, non-zero means an error
occurred, see libcurl-errors(3).
CURLOPT_PROXY_SSLVERSION(3), CURLOPT_SSLVERSION(3),
CURLOPT_SSL_OPTIONS(3)
libcurl 2026-04-29 CURLOPT_USE_SSL(3)
NAME
CURLOPT_USE_SSL - request using SSL / TLS for the transfer
SYNOPSIS
#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_USE_SSL, long level);
DESCRIPTION
Pass a long using one of the values from below, to make libcurl use
your desired level of SSL for the transfer.
These are all protocols that start out plain text and get "upgraded"
to SSL using the STARTTLS command.
This is for enabling SSL/TLS when you use FTP, SMTP, POP3, IMAP etc.
CURLUSESSL_NONE
Do not attempt to use SSL.
CURLUSESSL_TRY
Try using SSL, proceed as normal otherwise. Note that server
may close the connection if the negotiation fails. This level
is insecure and should be avoided since it allows the
connection to remain unprotected.
CURLUSESSL_CONTROL
Require SSL for the control connection or fail with
CURLE_USE_SSL_FAILED. This level is partially insecure and
should be avoided since it lets the data connection remain
unprotected.
This level is meant for FTP, since that is the only protocol
with separate connections for control and data. If used for
IMAP, POP3 or SMTP it equals CURLUSESSL_ALL.
CURLUSESSL_ALL
Require SSL for all communication or fail with
CURLE_USE_SSL_FAILED.
DEFAULT
CURLUSESSL_NONE
PROTOCOLS
This functionality affects ftp, imap, pop3 and smtp
EXAMPLE
int main(void)
{
CURL *curl = curl_easy_init();
if(curl) {
CURLcode result;
curl_easy_setopt(curl, CURLOPT_URL, "ftp://example.com/dir/file.ext");
/* require use of SSL for this, or fail */
curl_easy_setopt(curl, CURLOPT_USE_SSL, CURLUSESSL_ALL);
/* Perform the request */
result = curl_easy_perform(curl);
curl_easy_cleanup(curl);
}
}
HISTORY
This option was known as CURLOPT_FTP_SSL up to 7.16.4. Supported by
LDAP since 7.81.0. Fully supported by the OpenLDAP backend only.
CURLUSESSL_* enums became long types in 8.13.0, prior to this version
a long cast was necessary when passed to curl_easy_setopt(3).
AVAILABILITY
Added in curl 7.17.0
RETURN VALUE
curl_easy_setopt(3) returns a CURLcode indicating success or error.
CURLE_OK (0) means everything was OK, non-zero means an error
occurred, see libcurl-errors(3).
SEE ALSO
CURLOPT_PROXY_SSLVERSION(3), CURLOPT_SSLVERSION(3),
CURLOPT_SSL_OPTIONS(3)
libcurl 2026-04-29 CURLOPT_USE_SSL(3)