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> It'll automatically add keys to your agent the first time you use them during a session If you have more than one private key in your agent, then SSH will tr

> It'll automatically add keys to your agent the first time you use them during a session If you have more than one private key in your agent, then SSH will try each one sequentially. That can lead to mistakenly getting banned by monitoring software for what can appear indistinguishable to be an authentication attack. Not to mention the wrongness of presenting "any and all keys" to any host you connect to. If you have multiple keys in your agent, you _really_ should manually configure what key to present using `-i` or `IdentityFile`. But you should also use `IdentitiesOnly` too.

krferriter 7y ago
I don't understand what `IdentitiesOnly` does. If I have `IdentityFile`s defined for hosts in ssh_config, doesn't that already accomplish what this does? Can you explain what situation `IdentitiesOnly` covers that is different from `IdentityFile`?
- webvictim 7y ago
  Author here. If you specify an IdentityFile then that’ll be tried first (as an explicit identity) but if that doesn’t work then by default, ssh-agent identities will be tried sequentially afterwards. IdentitiesOnly suppresses that behaviour.
shawnz 7y ago
> If you have multiple keys in your agent, you _really_ should manually configure what key to present using `-i` or `IdentityFile`. If you specify -i or IdentityFile, the agent isn't used at all. You will have to type the keyfile password even if the key is in the agent, therefore making the agent useless. This "feature" has been a big annoyance for me, since I like to use different keys per machine.
- kadoban 7y ago
  There's no way that's true. I just checked and I have that option set on many of my ssh aliases, and ssh-agent functions exactly as expected. Maybe it depends on version or something? I've had the same config for years though over several very different OSes and presumably versions of everything.
  - shawnz 7y ago
    Wow, you're right. I tried again just now and it worked fine. In the past I tried for some time to get this setup working and was never able to do it. I don't know what I was doing wrong.
    - manuel_w 7y ago
      > If you specify -i or IdentityFile, the agent isn't used at all. You will have to type the keyfile password even if the key is in the agent, therefore making the agent useless. I thought so as well, so the reply to this message surprised. I looked into it, and the following is the case on my Debian 18.04 machine running KDE: With specifying the key through `IdentityFile` I can happily connect without a running ssh-agent. So it's true, that it can do without using the ssh-agent. But if the key has a password, it will prompt for it everytime it's used. I wouldn't phrase it "the agent isn't used at all", though, because for when ssh-agent is running, and it contains the key+password, it seems to happily use that agent, as it doesn't prompt for the password anymore. Side note: If my understanding is correct, `IdentifyFile` lessens the need for consulting the ssh-agent as stated above, but, except from consulting it for the key password, the agent might be consulted for one more reason as well: Iterating over keys if using the specified one proved unfruitful. For this to stop, you'd have to specify `IdentitiesOnly yes` as well. But this I didn't test, so it's based on theoretical understanding only. Edit: Oh, the last part was already explained in some other thread which branched of from this. So this post didn't actually provide some new insights, it seems.
deleted 7y ago
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krferriter 7y ago

I don't understand what `IdentitiesOnly` does. If I have `IdentityFile`s defined for hosts in ssh_config, doesn't that already accomplish what this does? Can you explain what situation `IdentitiesOnly` covers that is different from `IdentityFile`?

webvictim 7y ago
Author here. If you specify an IdentityFile then that’ll be tried first (as an explicit identity) but if that doesn’t work then by default, ssh-agent identities will be tried sequentially afterwards. IdentitiesOnly suppresses that behaviour.

shawnz 7y ago

> If you have multiple keys in your agent, you _really_ should manually configure what key to present using `-i` or `IdentityFile`. If you specify -i or IdentityFile, the agent isn't used at all. You will have to type the keyfile password even if the key is in the agent, therefore making the agent useless. This "feature" has been a big annoyance for me, since I like to use different keys per machine.

kadoban 7y ago
There's no way that's true. I just checked and I have that option set on many of my ssh aliases, and ssh-agent functions exactly as expected. Maybe it depends on version or something? I've had the same config for years though over several very different OSes and presumably versions of everything.
- shawnz 7y ago
  Wow, you're right. I tried again just now and it worked fine. In the past I tried for some time to get this setup working and was never able to do it. I don't know what I was doing wrong.
  - manuel_w 7y ago
    > If you specify -i or IdentityFile, the agent isn't used at all. You will have to type the keyfile password even if the key is in the agent, therefore making the agent useless. I thought so as well, so the reply to this message surprised. I looked into it, and the following is the case on my Debian 18.04 machine running KDE: With specifying the key through `IdentityFile` I can happily connect without a running ssh-agent. So it's true, that it can do without using the ssh-agent. But if the key has a password, it will prompt for it everytime it's used. I wouldn't phrase it "the agent isn't used at all", though, because for when ssh-agent is running, and it contains the key+password, it seems to happily use that agent, as it doesn't prompt for the password anymore. Side note: If my understanding is correct, `IdentifyFile` lessens the need for consulting the ssh-agent as stated above, but, except from consulting it for the key password, the agent might be consulted for one more reason as well: Iterating over keys if using the specified one proved unfruitful. For this to stop, you'd have to specify `IdentitiesOnly yes` as well. But this I didn't test, so it's based on theoretical understanding only. Edit: Oh, the last part was already explained in some other thread which branched of from this. So this post didn't actually provide some new insights, it seems.

deleted 7y ago

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