Command to remove a ssh authorized key on server

Is there a command (or a one-liner) to remove a ssh key on a server? Something like the opposite of ssh-copy-id?

As Ignatio suggested this can be done with grep -v.

Here is a example which removes the key containing some unique string or just deletes the authorized_keys file when no other key remains.

if test -f $HOME/.ssh/authorized_keys; then
  if grep -v "some unique string" $HOME/.ssh/authorized_keys > $HOME/.ssh/tmp; then
    cat $HOME/.ssh/tmp > $HOME/.ssh/authorized_keys && rm $HOME/.ssh/tmp;
  else
    rm $HOME/.ssh/authorized_keys && rm $HOME/.ssh/tmp;
  fi;
fi

Replace some unique string with something that only exists in the key you wish to remove.

As a oneliner over ssh this becomes

ssh hostname 'if test -f $HOME/.ssh/authorized_keys; then if grep -v "some unique string" $HOME/.ssh/authorized_keys > $HOME/.ssh/tmp; then cat $HOME/.ssh/tmp > $HOME/.ssh/authorized_keys && rm $HOME/.ssh/tmp; else rm $HOME/.ssh/authorized_keys && rm $HOME/.ssh/tmp; fi; fi'

Tested on Linux (SLES) and HP-UX.

sed provides a compact solution:

sed -i.bak '/REGEX_MATCHING_KEY/d' ~/.ssh/authorized_keys

This will save the original authorized_keys in authorized_keys.bak. If you don't want the backup then just change -i.bak to -i.

You can even remove multiple keys:

sed -i.bak '/REGEX1/d; /REGEX2/d' ~/.ssh/authorized_keys

The only tricky bit here is special characters in the regex need to be escaped.

Nope. You'll need to SSH in and use sed or grep to remove the key from the file.

Phil already answered this question but I want to do addition and make it easier for you. And since you are asking reverse of ssh-copy-id, I am assuming you want to run it on authorized machine.

ssh keys only contains base64 characters. So you can use a char as sed delimiter that not in that list. Let us use '#'.

ssh root@<hostname> -o PasswordAuthentication=no "sed -i.bak 's#`cat ~/.ssh/id_rsa.pub`##' ~/.ssh/authorized_keys"

Replace hostname with the server IP.

PasswordAuthentication option will cause ssh fail if it ask password

Command to remove a ssh authorized key on server

Related

Recent Posts