MaxSessions

MaxSessions is a configuration directive used by the OpenSSH server to limit the number of concurrent, multiplexed sessions that can be opened over a single SSH connection after authentication. In OpenSSH, a single network connection can carry multiple channels, and each session channel can host a command, a shell, or other subsystems. MaxSessions caps the total number of such sessions per connection, helping to control resource usage and reduce the impact of abusive or misconfigured clients.

The directive is configured in the server's sshd_config file, typically /etc/ssh/sshd_config. Administrators set a numeric value such as "MaxSessions 10" to enforce the limit; the higher the value, the more sessions are permitted per connection. After changing the value, the SSH service must be restarted or reloaded for the change to take effect. The default on many installations is 10, though distributions may vary.

Impact and considerations: Setting MaxSessions balances usability against resource protection. A higher limit benefits users who rely on multiple parallel sessions from a single connection, while a lower limit reduces memory and process usage on the server. Contexts such as automation, multiplexed workflows, and shared hosts should be taken into account.

See also: MaxStartups, ssh, sshd_config.