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I have two instances running on my aws. I have the same keypair for both of them. I was using both instances for long time. but today I am getting an error on one instance while trying to login through terminal if I run this command.

ssh -i mypem.pem ec2-user@52.xx.xxx.xxx

Permission denied (publickey).

But If I try to login to other instance with the same pem file. It works and I can successfully login to it.

I have tried all the solutions

• 
  Permission denied (publickey) when SSH Access to Amazon EC2 instance and


• Trying to SSH into an Amazon Ec2 instance - permission error

but nothing works for me

If I do

ssh -i mypem.pem ec2-user@52.xx.xxx.xxx -v

the result is:

OpenSSH_7.4p1, LibreSSL 2.5.0

debug1: Reading configuration data /etc/ssh/ssh_config

debug1: Connecting to 52.xx.xxx.xxx [52.xx.xxx.xxx] port 22.

debug1: Connection established.

debug1: key_load_public: No such file or directory

debug1: identity file mypem.pem type -1

debug1: key_load_public: No such file or directory

debug1: identity file mypem.pem-cert type -1

debug1: Enabling compatibility mode for protocol 2.0

debug1: Local version string SSH-2.0-OpenSSH_7.4

debug1: Remote protocol version 2.0, remote software version OpenSSH_7.4

debug1: match: OpenSSH_7.4 pat OpenSSH* compat 0x04000000

debug1: Authenticating to 52.xx.xxx.xxx as 'ec2-user'

debug1: SSH2_MSG_KEXINIT sent

debug1: SSH2_MSG_KEXINIT received

debug1: kex: algorithm: curve25519-sha256

debug1: kex: host key algorithm: ecdsa-sha2-nistp256

debug1: kex: server->client cipher: chacha20-poly1305@openssh.com MAC: <implicit> compression: none

debug1: kex: client->server cipher: chacha20-poly1305@openssh.com MAC: <implicit> compression: none

debug1: expecting SSH2_MSG_KEX_ECDH_REPLY

debug1: Server host key: mykeyhere

debug1: Host '52.xx.xxx.xxx' is known and matches the ECDSA host key.

debug1: Found key in /Users/myusername/.ssh/known_hosts:6

debug1: rekey after 134217728 blocks

debug1: SSH2_MSG_NEWKEYS sent

debug1: expecting SSH2_MSG_NEWKEYS

debug1: SSH2_MSG_NEWKEYS received

debug1: rekey after 134217728 blocks

debug1: SSH2_MSG_EXT_INFO received

debug1: kex_input_ext_info: server-sig-algs=<rsa-sha2-256,rsa-sha2-512>

debug1: SSH2_MSG_SERVICE_ACCEPT received

debug1: Authentications that can continue: publickey

debug1: Next authentication method: publickey

debug1: Offering RSA public key: /Users/myusername/.ssh/mypem.pem

debug1: Authentications that can continue: publickey

debug1: Trying private key: mypem.pem

debug1: Authentications that can continue: publickey

debug1: No more authentication methods to try.

Permission denied (publickey).

What I have tried

chmod 400 mypem.pem

I have also tried this

sudo ssh -i amazonec2.pem ec2-xxx-xxx-xxx-xxx.us-west 2.compute.amazonaws.com

Got this

Please login as the user "ec2-user" rather than the user "root"

then I did this

sudo ssh -i amazonec2.pem ec2-xxx-xxx-xxx-xxx.us-west-2.compute.amazonaws.com -l ec2-user

I got

Permission denied (publickey)

If I try to login to other instance with the same key. I can successfully login. Please help what actually went wrong here

Security Group on my instance is this:

If you are not running Amazon Linux, you have to change the username (ec2-user) for specific OS.

In my case, I'm using an Ubuntu server, and I connect using ubuntu@xxx.xx.xxx.xxx.