{"id":2535,"date":"2020-07-04T13:00:00","date_gmt":"2020-07-04T12:00:00","guid":{"rendered":"https:\/\/chewett.co.uk\/blog\/?p=2535"},"modified":"2020-07-09T23:55:56","modified_gmt":"2020-07-09T22:55:56","slug":"fixing-ssh-keygen-unknown-option-g-or-t-on-ubuntu-20-04","status":"publish","type":"post","link":"https:\/\/chewett.co.uk\/blog\/2535\/fixing-ssh-keygen-unknown-option-g-or-t-on-ubuntu-20-04\/","title":{"rendered":"Fixing ssh-keygen Unknown Option -G or -T on Ubuntu 20.04"},"content":{"rendered":"\n
\"\"<\/figure>\n\n\n\n

This blog post talks about how you can resolve the problem “ssh-keygen Unknown Option -G” on Ubuntu 20.04.<\/p>\n\n\n\n\n\n\n\n

What is ssh-keygen -G and -T used for?<\/h2>\n\n\n\n

The command ssh-keygen -G<\/code> was originally used to generate a list of prime numbers that could be used for key exchange. <\/p>\n\n\n\n

Typically the list of primes to use are pre-generated as it can take some time. By regenerating them you can increase the security of key exchange protocols marginally.<\/p>\n\n\n\n

Once the list or primes are generated you then need to screen them to check they are not inherently weak. To do this you would normally then call ssh-keygen -T<\/code> on the list of generated primes to verify they were valid.<\/p>\n\n\n\n

Once done you will have a file which can be used to replace your \/etc\/ssh\/moduli<\/code> file.<\/p>\n\n\n\n

The new way of generating Moduli instead of -G and -T<\/h2>\n\n\n\n

The latest version of OpenSSH which Ubuntu 20.04 comes bundled with has changed the commands. Previously you would run the following commands.<\/p>\n\n\n

\nssh-keygen -G moduli-2048.candidates -b 2048\nssh-keygen -T moduli-2048 -f moduli-2048.candidates\n<\/pre><\/div>\n\n\n
To achieve the same outcome with the new OpenSSH version you should use the following commands.<\/p>\n\n\n
\nssh-keygen -M generate -O bits=2048 moduli-2048.candidates\nssh-keygen -M screen -f moduli-2048.candidates moduli-2048\n<\/pre><\/div>\n\n\n
This will generate the same file as before which then can be used to replace your current \/etc\/ssh\/moduli<\/code> file.<\/p>\n\n\n\n
This can be done with the following commands.<\/p>\n\n\n
\ncp moduli-2048 \/etc\/ssh\/moduli\nrm moduli-2048\n<\/pre><\/div>\n\n\n
Once done SSH on your computer will be slightly more secure as you are using a new random set of prime numbers.<\/p>\n\n\n\n
If this worked for you or you have any questions post a comment below so I know if it works. Thanks!<\/p>\n","protected":false},"excerpt":{"rendered":"
This blog post talks about how you can resolve the problem “ssh-keygen Unknown Option -G” on Ubuntu 20.04.<\/p>\n","protected":false},"author":1,"featured_media":2566,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_exactmetrics_skip_tracking":false,"_exactmetrics_sitenote_active":false,"_exactmetrics_sitenote_note":"","_exactmetrics_sitenote_category":0,"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"Today I talk about Fixing ssh-keygen Unknown Option -G or -T on #Ubuntu 20.04 #OpenSSH","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[3],"tags":[13,39,388,147,389,390],"class_list":["post-2535","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-fixes","tag-fix","tag-linux","tag-openssh","tag-ubuntu","tag-ubuntu-20-04","tag-ubuntu-20-04-server"],"wppr_data":{"cwp_meta_box_check":"No"},"jetpack_publicize_connections":[],"jetpack_featured_media_url":"https:\/\/i0.wp.com\/chewett.co.uk\/blog\/wp-content\/uploads\/2020\/07\/sshkeygen_ubuntu2004-1.jpg?fit=1200%2C628&ssl=1","jetpack_shortlink":"https:\/\/wp.me\/p2toWX-ET","jetpack_sharing_enabled":true,"jetpack-related-posts":[{"id":2610,"url":"https:\/\/chewett.co.uk\/blog\/2610\/using-virtualbox-shared-folder-on-ubuntu-20-04\/","url_meta":{"origin":2535,"position":0},"title":"Using Virtualbox Shared Folder on Ubuntu 20.04","author":"Chewett","date":"September 12, 2020","format":false,"excerpt":"This post explains how you can configure Virtualbox Shared Folders for Ubuntu 20.04. 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