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curl (libcurl)

Published on 2023-03-28

Table of contents

  1. What is it?
  2. Issue sample
  3. All Platforms
  4. Certificate Verification in Windows/macOS
  5. Certificate Verification in Linux

What is it?

curl is used in command lines or scripts to transfer data.

Official Documentation

You can always check the general troubleshooting guide before continuing.

Issue sample

The error might look like this when using curl (libcurl):

When used as command-line tool:

curl: (60) SSL certificate problem: unable to get local issuer certificate

Depending on the use of libcurl in other frameworks and apps the error message might be formatted differently.

All Platforms

Curl and especially libcurl are the basis for network traffic in many other frameworks and applications like php, python, git, and many many more. This is the reason why many guides on this site point to this place to fix the certificate issue.

The curl command-line can use the argument --cacert to point to a trusted CA certificate file for a single call. Additionally curl and libcurl support the environment variables CURL_CA_BUNDLE which can be pointed to a certificate bundle file containing trusted CA certificates in pem - Base64 format.

Since libcurl is the base for other frameworks and applications, you can use the curl command-line to investigate certificate issues on your machine as shown here.

Certificate Verification in Windows/macOS

If libcurl was built with Schannel (Microsoft’s native TLS engine) or Secure Transport (Apple’s native TLS engine) support, then libcurl will still perform peer certificate verification, but instead of using a CA cert bundle, it will use the certificates that are built into the OS. These are the same certificates that appear in the Internet Options control panel (under Windows) or Keychain Access application (under OS X). Any custom security rules for certificates will be honored.

Source: curl documentation

An example for libcurl with built-in Schannel support is the Git for Windows Installer. Here you can use a configuration like the following to enable the use use of the Native Windows Certificate Store instead of a certificate bundle file:

git config --global http.sslBackend schannel

More information can be found here.

Certificate Verification in Linux

If libcurl was built with NSS support, then depending on the OS distribution, it is probably required to take some additional steps to use the system-wide CA cert db. Red Hat ships with an additional module,, which enables NSS to read the OpenSSL PEM CA bundle. On openSUSE you can install p11-kit-nss-trust which makes NSS use the system wide CA certificate store.

Source: curl documentation