ssh private key のパスフレーズを変更する

毎回忘れるのでメモ代わりに。ssh-keygen で変更できます

$ ssh-keygen -p -f ~/.ssh/id_rsa
Enter old passphrase: 
Key has comment '.ssh/id_rsa' 
Enter new passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved with the new passphrase.