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On Linux, start the OpenSSH server with sudo systemctl start ssh.service on Ubuntu and Debian, or sudo systemctl start sshd on RHEL, Fedora, CentOS, and Oracle Linux. To start it now and have it start at boot, use sudo systemctl enable --now with the matching service name.
Start the SSH server on your Linux distribution
The command verb is start; the service unit name varies by distribution family.
| Distribution family | Start now | Enable at boot and start now |
|---|---|---|
| Ubuntu or Debian with systemd | sudo systemctl start ssh.service |
sudo systemctl enable --now ssh.service |
| RHEL, Fedora, CentOS, or Oracle Linux with systemd | sudo systemctl start sshd |
sudo systemctl enable --now sshd |
| Older SysV-based systems | /sbin/service sshd start |
Boot enablement varies by system; the archived Red Hat procedure documents the start command. |
Ubuntu’s server guide uses the ssh.service unit, while Oracle Linux documents starting sshd. See Canonical’s Ubuntu OpenSSH server guide and Oracle Linux’s OpenSSH guide. For older SysV systems, see Red Hat’s archived guide.
Check the service name if you are unsure
Some distributions use ssh.service; others use sshd.service. Ask systemd which units are installed:
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systemctl list-unit-files | grep -E '^(ssh|sshd).service'
Use the unit that appears on your system. The service manager accepts the abbreviated forms ssh and sshd as well as the explicit .service suffix.
Install, validate, start, and verify
- Install the server package if needed. If the service or
sshdcommand is missing, install the distribution’s OpenSSH server package. The package is typically namedopenssh-server; Oracle Linux documentsopensshandopenssh-server. - Validate the configuration. Run
sudo sshd -t. The default server configuration file is/etc/ssh/sshd_config; command-line options can override values in that file. The Linux man-pages project’s sshd(8) manual documents the daemon and its options. - Start the appropriate unit. Use the Ubuntu/Debian or RHEL-family command above.
- Check service status. Run
sudo systemctl status ssh.serviceorsudo systemctl status sshd.service, matching the installed unit. - Check for a listening socket. Run
sudo ss -ltnp | grep ':22'. OpenSSH listens on port 22 by default, unless the server configuration changes the port. - Test from another machine. Connect with
ssh user@server, replacinguserandserverwith the account name and host address.
If the server does not start or accept connections
- The unit is not found: check the unit name with
systemctl list-unit-files | grep -E '^(ssh|sshd).service'. If neither appears, install the server package. - Configuration validation fails: review
/etc/ssh/sshd_configand correct the reported error, then runsudo sshd -tagain before starting the service. - The service fails during startup: inspect its journal with
sudo journalctl -u ssh.serviceorsudo journalctl -u sshd.service, using the unit name installed on your system. - The service is active but remote connections fail: verify that it is listening on the expected port and check the host’s firewall policy. If
Portis set in the server configuration, test that port rather than assuming the default.
When to run sshd directly
sudo /usr/sbin/sshd runs the daemon directly. This can be useful for diagnostics or custom supervision, but normal server operation should use the distribution’s service manager so startup remains integrated with service supervision and boot configuration. OpenSSH describes sshd as providing secure encrypted communications between two untrusted hosts over an insecure network; the OpenBSD sshd(8) manual and sshd_config(5) manual cover the daemon and its configuration.
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