SSH Configuration

$HOME/.ssh

An identify for the user is required:

~ $ ls .ssh/id_ed25519
.ssh/id_ed25519

If the output contains the following:

ls: cannot access '.ssh/id_ed25519': No such file or directory

then an identify needs to be created:

~ $ ssh-keygen -t ed25519 -f .ssh/id_ed25519 -C "username@localhost"

Two files, ‘id_ed25519’ and ‘id_ed25519.pub’ will be created in ‘$HOME/.ssh’

1. id_ed25519, the private key, do NOT share.

2. id_ed25519.pub, the public key, DO share.

Check permissions (ssh):

~ $ ls -alh .ssh
total ...K
drwx------ ... .
-rw------- ... id_ed25519
-rw------- ... id_ed25519.pub

The directory and all files must be restricted to owner access only.

See also

Wikipedia SSH

ssh-keygen options

From man ssh-keygen

NAME

ssh-keygen — OpenSSH authentication key utility

SYNOPSIS

ssh-keygen [-q] [-a rounds] [-b bits] [-C comment] [-f output_keyfile]

[-m format] [-N new_passphrase] [-O option] [-t dsa | ecdsa | ecdsa-sk | ed25519 | ed25519-sk | rsa] [-w provider] [-Z cipher]

ssh-keygen -p [-a rounds] [-f keyfile] [-m format] [-N new_passphrase]

[-P old_passphrase] [-Z cipher]

ssh-keygen -i [-f input_keyfile] [-m key_format]

ssh-keygen -e [-f input_keyfile] [-m key_format]

ssh-keygen -y [-f input_keyfile]

ssh-keygen -c [-a rounds] [-C comment] [-f keyfile] [-P passphrase]

ssh-keygen -l [-v] [-E fingerprint_hash] [-f input_keyfile]

ssh-keygen -B [-f input_keyfile]

ssh-keygen -D pkcs11

ssh-keygen -F hostname [-lv] [-f known_hosts_file]

ssh-keygen -H [-f known_hosts_file]

ssh-keygen -K [-a rounds] [-w provider]

ssh-keygen -R hostname [-f known_hosts_file]

ssh-keygen -r hostname [-g] [-f input_keyfile]

ssh-keygen -M generate [-O option] output_file

ssh-keygen -M screen [-f input_file] [-O option] output_file

ssh-keygen -I certificate_identity -s ca_key [-hU] [-D pkcs11_provider]

[-n principals] [-O option] [-V validity_interval] [-z serial_number] file …

ssh-keygen -L [-f input_keyfile]

ssh-keygen -A [-a rounds] [-f prefix_path]

ssh-keygen -k -f krl_file [-u] [-s ca_public] [-z version_number]

file …

ssh-keygen -Q [-l] -f krl_file file …

ssh-keygen -Y find-principals [-O option] -s signature_file -f

allowed_signers_file

ssh-keygen -Y match-principals -I signer_identity -f allowed_signers_file

ssh-keygen -Y check-novalidate [-O option] -n namespace -s signature_file

ssh-keygen -Y sign [-O option] -f key_file -n namespace file …

ssh-keygen -Y verify [-O option] -f allowed_signers_file -I

signer_identity -n namespace -s signature_file [-r revocation_file]