How do I check whether a Linux package is installed and which version it uses?
Use the package database that belongs to the distribution. An installed package version does not always identify the code currently running: a service may need a restart after an upgrade, or a custom binary may take precedence in its executable path. Verify the application separately when diagnosing a version mismatch.
Before you start
- An authorised SSH session on the Linux server.
Instructions
1. Query the appropriate package database
The examples inspect OpenSSH server packages without changing them. Run the Debian/Ubuntu command or the RPM-family command, not both as an installation procedure.
dpkg-query -W -f='${Status} ${Version}\n' openssh-serverDebian/Ubuntu: installed status should include install ok installed; a package record alone is not enough.
rpm -q openssh-serverRHEL-family: the result includes the installed package build; not installed is a normal negative result.
2. Check where the executable comes from
Identify the actual command or service binary used by the application. A binary installed under /usr/local can be independent of the distribution package.
command -v ssh
ssh -VThis example reads the SSH client location and version. The client and server package versions are related but not interchangeable evidence.
Check the result
- The package database reports the expected installed state, and the relevant application’s own version/status confirms the intended running software.
Troubleshooting
- The command works but no package is found
- It may be manually installed, bundled with an application, or named differently. Identify the exact executable and its owner before changing packages.
Official references
Use the documentation for your installed version when a flag, service name or platform feature differs.