How to test for open port without telnet

April 5, 2014June 23, 2018 - - Comment is Closed

The telnet client is no longer being installed by default on secure systems. So, how do you check that you can get to a remote port, like a mail relay? There’s been a trick in bash for a while, that I didn’t know about. Here’s how to get an idea:

2014-04-05 07:35:56 ec2-user@ip-172-31-9-61:~
0$ cat < /dev/tcp/smtp.gmail.com/25
220 mx.google.com ESMTP st4sm62108693pab.34 - gsmtp
^C

This is great! I need to play more with it, but it works for a start.

George Robinson has been taming technology since 1981. His first bitter taste of UNIX was in 1987 with Xenix 2.1.1. George's youth was spent in building electronics and writing programs to post on the local BBS. In high school, he became involved in student radio and was hired by the top station in the market. After high school, he spent two years traveling the western United States and Canada with REACH Youth Ministries. George double majored in Psychology and Music Theory at Rocky Mountain College in Billings, Montana. During college, the Internet wave hit Montana and his hobby became highly in-demand skills. George finally went pro in 1998 and has been trying to automate himself out of a job ever since. He rode the Internet boom to Orange county. Making the most of his diverse experience, he pursues a career in systems administration and DevOps. He has had roles in numerous startups and has been a systems administrator in enterprises like Verizon Wireless, Yahoo, Nestlé & Fico.