I am not familiar with CentOS but you shouldn't use older versions and any version older than 3.3. can no longer connect to Electrum servers due to previous incidents with phishing messages.
The message is also posted on the official download page on Electrum.
Warning: Electrum versions older than 3.3 can no longer connect to public servers, and must be upgraded. This is in order to prevent user exposure to phishing messages. Do not download Electrum from any another source than electrum.org.
https://electrum.org/#download