CURLOPT_SSH_KNOWNHOSTS(3) Library Functions Manual CURLOPT_SSH_KNOWNHOSTS(3)
NAME
CURLOPT_SSH_KNOWNHOSTS - filename holding the SSH known hosts
SYNOPSIS
#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSH_KNOWNHOSTS, char *fname);
DESCRIPTION
Pass a pointer to a null-terminated string holding the filename of the
known_host file to use. The known_hosts file should use the OpenSSH
file format. If this file is specified, libcurl only accepts
connections with hosts that are known and present in that file, with a
matching public key. Use CURLOPT_SSH_KEYFUNCTION(3) to alter the
default behavior on host and key matches and mismatches.
We strongly suggest users doing SCP or SFTP transfers to set this
option to make sure that the network communication is done with the
intended server and not an impostor.
The application does not have to keep the string around after setting
this option.
Using this option multiple times makes the last set string override the
previous ones. Set it to NULL to disable its use again.
This option is only consulted when libcurl establishes a new
connection. Once a connection has been created and its host key
verified against the known hosts file, it is deemed vetted and may be
reused by libcurl without re-running the known hosts check, even if you
later change SSH host verification options (including setting this
option to NULL or using CURLOPT_SSH_HOST_PUBLIC_KEY_SHA256(3) or
CURLOPT_SSH_HOST_PUBLIC_KEY_MD5(3)). Such changes only affect
subsequently created connections; existing cached connections can
continue to be reused with the verification that was in effect when
they were first established. If you need to force re-verification with
the new settings, use CURLOPT_FRESH_CONNECT(3) or
CURLOPT_FORBID_REUSE(3) to avoid reusing the old connection.
DEFAULT
NULL
PROTOCOLS
This functionality affects scp and sftp
EXAMPLE
int main(void)
{
CURL *curl = curl_easy_init();
if(curl) {
CURLcode result;
curl_easy_setopt(curl, CURLOPT_URL, "sftp://example.com/file");
curl_easy_setopt(curl, CURLOPT_SSH_KNOWNHOSTS,
"/home/clarkkent/.ssh/known_hosts");
result = curl_easy_perform(curl);
curl_easy_cleanup(curl);
}
}
AVAILABILITY
Added in curl 7.19.6
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_SSH_AUTH_TYPES(3), CURLOPT_SSH_HOST_PUBLIC_KEY_MD5(3),
CURLOPT_SSH_HOST_PUBLIC_KEY_SHA256(3)
libcurl 2026-06-09 CURLOPT_SSH_KNOWNHOSTS(3)
curl 8.20.0 - Generated Wed Jun 10 16:32:14 CDT 2026