SSH: `Permission denied (publickey)` when connecting to my server

Question

I generated a key with `ssh-keygen` and copied the `.pub` content into the server's `authorized_keys`, but I still get `Permission denied (publickey)`.

Accepted Answer

Go through the usual suspects:

1. **Verbose output** tells you which keys are being tried:
```bash
ssh -v user@server
```
2. **Permissions on the server**. SSH silently ignores keys when these are too open:
```bash
chmod 700 ~/.ssh
chmod 600 ~/.ssh/authorized_keys
chown -R $USER:$USER ~/.ssh
```
   (The home directory must not be group- or world-writable either.)
3. **Right user**: the key must be in `/home/<that-user>/.ssh/authorized_keys` for the user you're logging in as.
4. **Right key on the client**: if it's not a default name, specify it: `ssh -i ~/.ssh/mykey user@server`, or add a block to `~/.ssh/config`:
```
Host prod
  HostName 203.0.113.10
  User deploy
  IdentityFile ~/.ssh/mykey
```
5. **Pasting issues**: the key must be one single line.
6. Server logs: `sudo journalctl -u ssh` (or `/var/log/auth.log`) shows the exact reason.

`ssh-copy-id user@server` avoids most of these mistakes.

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