Copilot Certificate Errors on Linux: Check the Client and CA Trust Store

Official documentation checked October 14, 2026.

A missing CA bundle can cause TLS failures on Linux, but “Copilot on Linux” does not identify one universal application or configuration file. First establish whether the failure is in a browser-based Microsoft Copilot session, a GitHub Copilot editor extension, or another client. The repair must apply to the environment that actually makes the connection.

1. Confirm which trust store the failing client uses

Record the application and extension versions, distribution release, installation method, and exact certificate error. A browser, a container, a remote development host, and a locally installed editor may use different trust stores. Updating the host will not automatically repair a separate container or every sandboxed application.

For GitHub Copilot’s documented editor integration on Linux, GitHub lists /etc/ssl/certs/ca-certificates.crt and /etc/ssl/certs/ca-bundle.crt among its certificate-discovery locations. See GitHub’s network troubleshooting guide. Do not generalize those paths to every product named Copilot.

There is no general Microsoft Copilot /etc/copilot/copilot.conf file with a documented ca_bundle setting. Do not create that file, replace system symlinks, or set a random certificate environment variable unless the specific client’s documentation requires it.

2. Restore the distribution’s managed certificates

Check whether the CA package is installed and whether the expected bundle is readable. On a managed computer, obtain approval before reinstalling packages or rebuilding trust. Use signed distribution repositories; never download a replacement CA bundle from an arbitrary troubleshooting site.

For Ubuntu, the standard package and trust update commands are:

sudo apt-get install ca-certificates
sudo update-ca-certificates
ls -l /etc/ssl/certs/ca-certificates.crt

The package manager’s successful completion matters more than merely finding a nonempty file. If installed package files are damaged, use the distribution’s package-repair procedure. Ubuntu documents the generated bundle and system-store scope in its CA trust guide. Snap-packaged apps can require separate treatment.

For RHEL, verify the ca-certificates package and use the distribution’s shared trust mechanism. After an approved trust-source correction, the documented regeneration command is:

sudo update-ca-trust extract

See Red Hat’s shared-certificate documentation. For SUSE or another distribution, use its release-specific instructions rather than assuming Debian commands or bundle locations are interchangeable.

3. Handle a corporate CA as a trust decision

If an approved proxy signs the certificate presented to the client, reinstalling public CA certificates may not add that organization’s private CA. Obtain the correct public CA certificate through an authenticated IT channel and verify its fingerprint with the PKI owner. Do not generate a new self-signed certificate as a substitute or trust the failing website’s certificate simply because it was presented.

For an approved Ubuntu PEM CA certificate, the documented local trust directory is /usr/local/share/ca-certificates/, with a .crt extension, followed by update-ca-certificates. RHEL uses its own trust-anchor directories and update-ca-trust. Apply the change in the actual execution environment and restart the affected client.

Adding a root can authorize interception of other connections. GitHub’s custom-certificate guidance explicitly warns about this trust implication. Keep strict TLS validation enabled; an insecure flag is not a permanent repair.

4. Test the real endpoint and investigate remaining errors

For GitHub Copilot Chat in an editor, its documented diagnostic endpoint can be tested with validation enabled:

curl --verbose https://api.githubcopilot.com/_ping

A successful request checks that endpoint from that shell; it does not prove that a differently configured editor or browser works. Repeat the original Copilot action afterward. Do not use a successful request to a Microsoft login host as proof that GitHub Copilot endpoints are reachable.

If the failure remains, check the clock, expected issuer, complete certificate chain, proxy route, and client-specific diagnostics. Sanitize logs before sharing them. Do not install a second time service blindly, schedule weekly force-rebuilds of trust, or disable hostname/certificate verification. Escalate the precise failing client and endpoint so the administrator can repair the cause instead of repeatedly replacing the bundle.