Install puttygen in Ubuntu by
#apt-get install putty-tools
The the .ppk file is used by the Putty application as a Private key File and it needs to converted to a SSH Private Key file for using it in SSH remote passwordless access. (SSH uses .pem file for private key)
#puttygen keyfile.ppk -o id_rsa.pub -O public-openssh
Where “keyfile.ppk” is the PuTTY .ppk file to convert, and “id_rsa.pub” is the name of the converted key file.
Convert .ppk (putty file) TO .pem (ssh private key)
#puttygen keyfile.ppk -o id_rsa -O private-openssh
Where “keyfile.ppk” is the key file that is to be converted to – id_rsa which is the SSH private key. PuTTY stores both the private and public keys in the .ppk file, which is why you use the same file to convert both keys. You can now use both keys with OpenSSH.
Convert a .pem (ssh private key) TO .ppk (putty file) in Linux
#puttygen crowdfynd-stage.pem -o crowdfynd-stage.ppk
SSH ERROR : permission denied (public file)
This error happens for a variety of reasons — first we have to check is whether the user has a ssh login or not , then the private file mentioned in the command using -i flag shud be 600 etc are some of them.