---
c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
SPDX-License-Identifier: curl
Title: CURLOPT_SSH_KNOWNHOSTS
Section: 3
Source: libcurl
See-also:
  - CURLOPT_SSH_AUTH_TYPES (3)
  - CURLOPT_SSH_HOST_PUBLIC_KEY_MD5 (3)
  - CURLOPT_SSH_HOST_PUBLIC_KEY_SHA256 (3)
Protocol:
  - SFTP
  - SCP
Added-in: 7.19.6
---

# NAME

CURLOPT_SSH_KNOWNHOSTS - filename holding the SSH known hosts

# SYNOPSIS

~~~c
#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%

# EXAMPLE

~~~c
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%

# 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).
