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I have a strange issue where SSH won't properly connect with a private-key if the key file is in certain directories. I've setup the keys on a set of servers and the following command

ssh -i /root/privatekey keyuser@host.com

works fine and I login to the given host without getting prompted by a password, but this command:

ssh -i /etc/keyfiles/privatekey keyuser@host.com

gives me a password prompt. I've narrowed it down that this behavior occurs in only some sub-directories of /etc/. For example /etc/httpd1/ gives me a password prompt but /etc/httpd/ does not.

What I've checked so far:

  • All private key files used are identical (copied from the original file).
  • The private key file and directories used have identical permissions.
  • No relevant error messages in the server/client logs.
  • No interesting debug messages from ssh -v (it just seems to skip the key file).
  • It happens with connecting to different hosts.

After more testing it is not the actual directory name. For example:

mkdir /etc/test
cp /root/privatekey /etc/test
ssh -i /etc/test/privatekey keyuser@host.com    # Results in password prompt
cp /root/privatekey /etc/httpd                  # Existing directory
ls -ald test httpd
  # drwxr-xr-x 4 root root 4096 Mar  5 18:25 httpd
  # drwxr-xr-x 2 root root 4096 Mar  5 18:43 test
ssh -i /etc/httpd/privatekey keyuser@host.com   # Results in *no* prompt
rm -r test
cp -R /etc/httpd /etc/test
ssh -i /etc/test/privatekey keyuser@host.com   # Results in *no* prompt`

I'm sure its just something simple I've overlooked but I'm at a loss.

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The issue turned out to be a public key in the directory with the name privatekey.pub that was from another server. Deleting that public key file or replacing it with the correct one for the local server removed the password prompt. –  uesp Mar 6 '11 at 16:03
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2 Answers

up vote 0 down vote accepted

I suggest looking at 'ssh -vvv' output when connecting. Also increase the loglevel to DEBUG in your /etc/ssh/sshd_config. That should give you some idea of what is going on.

Are some of your subdirectories links and some real directories? I assume this has got to be some sort of weird permission problem somewhere.

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The likely reason is the permissions and ownership of the directories. ssh is paranoid and refuses a key based on the permissions of the parent directory as well as permissions on the key and the directory containing it.

I do this in my environment install:

    ln -fs $(PWD)/ssh3 $(INSTALL_DIR)/.ssh
    # Make sure the permissions are OK; ssh is paranoid
    chmod 700 ssh3
    find ssh3/ -type f -exec chmod 600 {} \;

It is known to work on CentOS 4 and 5.

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This sort of error should definitely be printed in your ssh server log, especially if you turn up the debug level... –  Phil Hollenback Mar 6 '11 at 0:12
    
It is the openssh client who is doing the check for the client private key. –  Mircea Vutcovici Mar 6 '11 at 0:40
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