Nagios Support Forum

We are using check_by_ssh where we need to open an ssh connection from a central server to remote hosts to collect metrics for monitoring needs.

1. What is the default limit on number of concurrent connections opened to a remote linux host.
2. What is the default limit on number of concurrent connections opened from any given server to remote hosts. Can this be altered.
3. In general what is the CPU/RAM usage per each ssh connection.

Thanks

Assuming OpenSSH for the client and server software.

1. What is the default limit on number of concurrent connections opened to a remote linux host.

I don't know that OpenSSH places restrictions on outbound connections. It assumes that there will be a restriction on the receiving side, if one is needed.

2. What is the default limit on number of concurrent connections opened from any given server to remote hosts. Can this be altered.

This can be altered on the remote host, in /etc/ssh/sshd_config. The setting you're looking for is MaxSessions. I don't think this is set by default.

3. In general what is the CPU/RAM usage per each ssh connection.

Just the ssh connection will barely even register on the system's load. What contributes to load is how much data goes over the ssh connection, and what cipher you've chosen. Usually a check will only return a line or two of data, so whatever additional load is created is rarely noticed.