update-ca-certificates

update-ca-certificates [OPTIONS]

--verbose, -v
    Enables verbose output, showing each certificate file processed and the actions taken. This is useful for debugging or understanding the command's operations.

--fresh
    Forces a complete rebuild of the certificate bundle. All existing symbolic links in /etc/ssl/certs/ are removed before new ones are created. This ensures no stale entries remain.

--disable-incremental
    Disables incremental updates. Even if only minor changes occurred, the entire certificate bundle is regenerated from scratch, similar to `--fresh` in its rebuild approach but specifically targets the bundle generation rather than link management.

--debug
    Enables debugging output, providing more detailed information about the script's execution flow. This option is typically used for script development or deep troubleshooting.

--help
    Displays a short help message with available options and exits.

The update-ca-certificates command is a utility used primarily on Debian-based Linux distributions to manage the system's trusted CA (Certificate Authority) certificates. Its main function is to consolidate certificates from various sources into a single, unified bundle, typically located at /etc/ssl/certs/ca-certificates.crt.

It processes certificate files from directories like /usr/local/share/ca-certificates/ (for locally added certificates) and those installed by packages. By default, it creates symbolic links in /etc/ssl/certs/ pointing to the actual certificate files, and then generates the combined ca-certificates.crt file.

This command is crucial for applications and services that rely on a trusted list of CAs for verifying SSL/TLS connections, such as web browsers, `wget`, `curl`, and `apt`. It ensures that your system trusts the necessary authorities to validate certificates presented by secure servers, protecting against man-in-the-middle attacks and ensuring secure communication.

This utility is primarily designed for Debian-based distributions (e.g., Ubuntu, Mint). Other Linux distributions might use different tools for managing CA certificates, such as update-pki or the trust command (on Fedora/RHEL).

Requires root privileges to execute, as it modifies system-wide configuration files in /etc/ssl/certs/ and other privileged directories.

For adding custom CA certificates, users should place them in /usr/local/share/ca-certificates/ (in PEM format with a .crt extension) and then run update-ca-certificates. Placing them directly in /etc/ssl/certs/ is discouraged as they might be overwritten or lead to inconsistencies.

To add your own trusted CA certificate, place the certificate file (which must be in PEM format and end with the .crt extension) into the /usr/local/share/ca-certificates/ directory. After placing the file, run sudo update-ca-certificates to incorporate it into the system's trusted bundle.

The command compiles all trusted certificates into a single file, typically located at /etc/ssl/certs/ca-certificates.crt. This consolidated bundle is then used by many applications and libraries (like OpenSSL and GnuTLS) that need a single source of truth for trusted CAs.

The update-ca-certificates command is automatically invoked by package management tools (like apt) whenever the `ca-certificates` package or any package providing new certificates is installed, updated, or removed, ensuring the system's trust store remains current.

The update-ca-certificates utility has been a fundamental component of Debian and Ubuntu for managing system-wide CA certificates for many years. It was developed to provide a standardized and automated way to compile and update the list of trusted root certificates from various sources, including those shipped by the distribution and custom user-provided certificates. Its development is closely tied to the `ca-certificates` package, which maintains the official list of trusted CAs, ensuring applications consistently have access to an up-to-date and reliable set of trust anchors.

ca-certificates(8), dpkg-reconfigure(8), c_rehash(1ssl), trust(1)