How to open .CRT files on Linux
To open .CRT files on Linux, open the .CRT file in a text editor first to see if it is PEM (it will show "BEGIN CERTIFICATE" blocks).
Step-by-step instructions
- Open the .CRT file in a text editor first to see if it is PEM (it will show "BEGIN CERTIFICATE" blocks).
- If you need to trust it system-wide, import it using your distribution’s certificate trust mechanism (varies by distro) rather than simply opening it as a document.
- If you only need to inspect it, use a certificate-viewing tool available on your desktop environment or command-line tooling.
Common issues
The .CRT opens as unreadable characters
This usually means the certificate is in DER (binary) encoding rather than PEM (text).
- Try opening it with the OS certificate viewer/import tool instead of a text editor.
- If you need a text form for copy/paste, obtain a PEM version from the issuer/export process rather than renaming the file.
Import/installation fails
The certificate may be corrupted, incomplete, not valid for the intended use, or missing required intermediate certificates in the chain.
- Re-download or re-export the certificate to ensure it is complete and unmodified.
- Verify you also have any required intermediate/CA certificates needed to build a valid trust chain.
The certificate is rejected as expired or not yet valid
X.509 certificates have validity dates, and systems will reject certificates outside the valid time window.
- Check the certificate validity dates in the certificate viewer.
- Confirm the device/system clock is correct; then obtain an updated/reissued certificate if it is genuinely expired.
Wrong file type: expecting a certificate but it’s something else
Some workflows use .crt loosely, but the most common meaning is an X.509 certificate; if the content doesn’t match, your tool may refuse it.
- Open the file in a text editor and look for PEM markers ("BEGIN CERTIFICATE").
- Confirm with the sender/system documentation whether you were supposed to receive a certificate, a CA bundle, or a different artifact.
Security note
A .CRT is typically a certificate (public data), but importing/installing it changes what your device trusts; only import certificates from sources you trust to avoid man-in-the-middle risks.