Sitaram Chamarty 7170ad9124 allow pubkey filename as extra argument to command in authkeys

2012-05-30 15:02:35 +05:30

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#sts ssh troubleshooting and tips

This document must be read in full the first time. If you start from some nice looking section in the middle it may not help you unless you're already an expert at ssh.

This document should help you troubleshoot ssh-related problems in installing and accessing gitolite. It also has a section of random ssh-related tips and tricks that gitolite can do.

TOC

IMPORTANT -- READ THIS FIRST

caveats

Before reading this document, it is mandatory to read and completely understand [this][ssh], which is a very detailed look at how gitolite uses ssh's features on the server side. Don't assume you know all that; if you did, you wouldn't be needing this document either!
This document, and others linked from this, together comprise all the help I can give you in terms of the ssh aspect of using gitolite. If you're installing gitolite, you're a "system admin", like it or not. Ssh is therefore a necessary skill. Please take the time to learn at least enough to get passwordless access working.
Please note that authentication is not really gitolite's job at all. I'd rather spend time on actual gitolite features, code, and documentation than authentication (i.e., ssh, in the common case).

Surprised? [This][auth] might help explain better.

naming conventions used

Your workstation is the client. Your userid on the client does not matter, and it has no relation to your gitolite username.
The server is called server and the "hosting user" is git. If this is an RPM/DEB install, the hosting user is probably called "gitolite", however we will use "git" in this document.

taking stock -- relevant files and directories

The client has a ~/.ssh containing a few keypairs. It may also have a config file.
The client also has a clone of the "gitolite-admin" repo, which contains a bunch of *.pub files in keydir. We assume this clone is in $HOME; if it is not, adjust instructions accordingly when needed.
The git user on the server has a ~/.ssh/authorized_keys file that the ssh daemon uses to authenticate incoming users. We often call this file authkeys to save typing, and it always means the one on the server (we're not interested in this file on the client side).
The server also has a ~/.gitolite/keydir which contains a bunch of *.pub files.

normal gitolite key handling

Here's how normal gitolite key handling works:

(On client) pub key changes like adding new ones, deleting old ones, etc., are done in the keydir directory in the gitolite-admin repo clone. Then the admin git adds and git commits those changes, then git pushes them to the server.
(On server) a successful push from the client makes git invoke the post-update hook in the gitolite-admin repo. This hook is installed by gitolite, and it does a bunch of things which are quite transparent to the admin, but we'll describe briefly here:
- The pubkey files from this push are checked-out into ~/.gitolite/keydir (and similarly the config files into ~/.gitolite/conf).
- The "compile" script then runs, which uses these files to populate ~/.ssh/authorized_keys on the server.
  
  The authkeys file may have other, (non-gitolite) keys also. Those lines are preserved. Gitolite only touches lines that are found between gitolite's "marker" lines (# gitolite start and # gitolite end).

common ssh problems

Since I'm pretty sure at least some of you didn't bother to read the "IMPORTANT: PLEASE READ FIRST" section above, let me take a minute to point you there again. Especially the first bullet.

Done? OK, read on...

The following problem(s) indicate that pubkey access is not working at all, so you should start with [appendix 1][stsapp1]. If that doesn't fix the problem, continue with the other appendices in sequence.

Running any git clone/fetch/ls-remote or just ssh git@server info asks you for a password.

The following problem(s) indicate that your pubkey is bypassing gitolite and going straight to a shell. You should start with [appendix 2][sshkeys-lint] and continue with the rest in sequence. [Appendix 5][ybpfail] has some background info.

Running ssh git@server info gets you the output of the GNU 'info' command instead of gitolite's version and access info.
Running git clone git@server:repositories/reponame (note presence of repositories/ in URL) works.

[A proper gitolite key will only let you git clone git@server:reponame (note absence of repositories/)]
You are able to clone repositories but are unable to push changes back (the error complains about the GL_BINDIR environment variable not being set, and the hooks/update failing in some way).

[If you run git remote -v you will find that your clone URL included the repositories/ described above!]
Conversely, using the correct syntax, git clone git@server:reponame (note absence of repositories/ in the URL), gets you fatal: 'reponame' does not appear to be a git repository, and yet you are sure 'reponame' exists, you haven't mis-spelled it, etc.

step by step

Since I'm pretty sure at least some of you didn't bother to read the "IMPORTANT: PLEASE READ FIRST" section above, let me take a minute to point you there again. Especially the first bullet.

Done? OK, now the general outline for ssh troubleshooting is this:

Make sure the server's overall setup even allows pubkey based login. I.e., check that git fetch/clone/ls-remote commands or a plain ssh git@server info do NOT ask for a password. If you do get asked for a password, see [appendix 1][stsapp1].
Match client-side pubkeys (~/.ssh/*.pub) with the server's authkeys file. To do this, run sshkeys-lint, which tells you in detail what key has what access. See [appendix 2][sshkeys-lint].
At this point, we know that we have the right key, and that if sshd receives that key, things will work. But we're not done yet. We still need to make sure that this specific key is being offered/sent by the client, instead of the default key. See [appendix 3][stsapp3] and [appendix 4][ssh-ha].

random tips, tricks, and notes

giving shell access to gitolite users

Thanks to an idea from Jesse Keating, a single key can allow both gitolite access and shell access.

To do this:

add the list of users who will have shell access -- one username per line, no extra whitespace -- to a plain text file of your choice.
put the name of this file in a new rc variable SHELL_USERS_LIST. For example it could be
```
SHELL_USERS_LIST        =>  "$ENV{HOME}/.gitolite.shell-users",
```
add the line 'Shell::input', to the INPUT list in the rc file.
add the line 'post-compile/ssh-authkeys-shell-users', to the POST_COMPILE list, after the 'post-compile/ssh-authkeys', line.

Then run gitolite compile; gitolite trigger POST_COMPILE or push a dummy change to the admin repo.

distinguishing one key from another

Since a user can have [more than one key][multi-key], it is sometimes useful to distinguish one key from another. Sshd does not tell you even the fingerprint of the key that finally matched, so normally all you have is the GL_USER env var.

However, if you replace

'post-compile/ssh-authkeys',

in the POST_COMPILE trigger list in the rc file with

'post-compile/ssh-authkeys --key-file-name',

then an extra argument is added after the username in the "command" variable of the authkeys file. That is, instead of this:

command="/home/g3/gitolite/src/gitolite-shell u3",no-port-forwarding,...

you get this:

command="/home/g3/gitolite/src/gitolite-shell u3 keydir/u3.pub",no-port-forwarding,...

You can then write an INPUT trigger to do whatever you need with the file name, which is in $ARGV[1] (the second argument). The actual file is available at $ENV{GL_ADMIN_BASE}/$ARGV[1] if you need its contents.

simulating ssh-copy-id

don't have ssh-copy-id? This is broadly what that command does, if you want to replicate it manually. The input is your pubkey, typically ~/.ssh/id_rsa.pub from your client/workstation.

It copies it to the server as some file.
It appends that file to ~/.ssh/authorized_keys on the server (creating it if it doesn't already exist).
It then makes sure that all these files/directories have go-w perms set (assuming user is "git"):
```
/home/git/.ssh/authorized_keys
/home/git/.ssh
/home/git
```

[Actually, sshd requires that even directories above ~ (/, /home, typically) also must be go-w, but that needs root. And typically they're already set that way anyway. (Or if they're not, you've got bigger problems than gitolite install not working!)]

problems with using non-openssh public keys

Gitolite accepts public keys only in openssh format. Trying to use an "ssh2" key (used by proprietary SSH software) will not be a happy experience. src/triggers/post-compile/ssh-authkeys can be made to detect non-openssh formats and automatically convert them; patches welcome!

The actual conversion command, if you want to just do it manually for now and be done with it, is:

ssh-keygen -i -f /tmp/ssh2/YourName.pub > /tmp/openssh/YourName.pub

then use the resulting pubkey as you normally would in gitolite.

windows issues

On windows, I have only used msysgit, and the openssh that comes with it. Over time, I have grown to distrust putty/plink due to the number of people who seem to have trouble when those beasts are involved (I myself have never used them for any kind of git access). If you have unusual ssh problems that just don't seem to have any explanation, try removing all traces of putty/plink, including environment variables, etc., and then try again.

Thankfully, someone contributed [this][putty].

#stsapp1 appendix 1: ssh daemon asks for a password

NOTE: This section should be useful to anyone trying to get password-less access working. It is not necessarily specific to gitolite, so keep that in mind if the wording feels a little more general than you were expecting.

You have generated a keypair on your workstation (ssh-keygen) and copied the public part of it (~/.ssh/id_rsa.pub, by default) to the server.

On the server you have appended this file to ~/.ssh/authorized_keys. Or you ran something, like the gitolite setup step during a gitolite install, which should have done that for you.

You now expect to log in without having to type in a password, but when you try, you are being asked for a password.

This is a quick checklist:

Make sure you're being asked for a password and not a passphrase. Do not confuse or mistake a prompt saying Enter passphrase for key '/home/sitaram/.ssh/id_rsa': for a password prompt from the remote server!

When you create an ssh keypair using ssh-keygen, you have the option of protecting it with a passphrase. When you subsequently use that keypair to access a remote host, your local ssh client needs to unlock the corresponding private key, and ssh will probably ask for the passphrase you set when you created the keypair.

You have two choices to avoid this prompt every time you try to use the private key. The first is to create keypairs without a passphrase (just hit enter when prompted for one). Be sure to add a passphrase later, once everything is working, using ssh-keygen -p.

The second is to use ssh-agent (or keychain, which in turn uses ssh-agent) or something like that to manage your keys. Other than discussing one more potential trouble-spot with ssh-agent (see below), further discussion of ssh-agent/keychain is out of scope of this document.
Ssh is very sensitive to permissions. An extremely conservative setup is given below, but be sure to do this on both the client and the server:
```
cd $HOME
chmod go-rwx .
chmod -R go-rwx .ssh
```
Actually, every component of the path to ~/.ssh/authorized_keys all the way upto the root directory must be at least chmod go-w. So be sure to check / and /home also.
While you're doing this, make sure the owner and group info for each of these components are correct. ls -ald ~ ~/.ssh ~/.ssh/authorized_keys will tell you what they are.
You may also want to check /etc/ssh/sshd_config to see if the "git" user is allowed to login at all. For example, if that file contains an AllowUsers config entry, then only users mentioned in that line are allowed to log in!
While you're in there, check that file does NOT have a setting for AuthorizedKeysFile. See man sshd_config for details. This setting is a show stopper for gitolite to use ssh.
Some OSs/distributions require that the "git" user should have a password and/or not be a locked account. You may want to check that as well.
If all that fails, log onto the server as root, cd /var/log, and look for a file called auth.log or secure or some such name. Look inside this file for messages matching the approximate time of your last attempt to login, to see if they tell you what is the problem.

#sshkeys-lint appendix 2: which key is which -- running sshkeys-lint

The sshkeys-lint program can be run on the server or the client. Run it with '-h' to get a help message.

On the server you can run gitolite sshkeys-lint and it will tell you, for each key in the admin directory's keydir, what access is available. This is especially good at finding duplicate keys and such.

To run it on the client you have to copy the file src/commands/sshkeys-lint from some gitolite clone, then follow these steps:

Get a copy of ~/.ssh/authorized_keys from the server and put it in /tmp/foo or something.
cd to ~/.ssh.
Run /path/to/sshkeys-lint *.pub < /tmp/foo.

Note that it is not trying to log in or anything -- it's just comparing fingerprints as computed by ssh-keygen -l.

If the pubkey file you're interested in appears to have the correct access to the server, you're done with this step.

Otherwise you have to rename some keypairs and try again to get the effect you need. Be careful:

Do not just rename the ".pub" file; you will have to rename the corresponding private key also (the one with the same basename but without an extension).
If you're running ssh-agent, you may have to delete (using ssh-add -D) and re-add identities for it to pick up the renamed ones correctly.

typical cause(s)

The admin often has passwordless shell access to git@server already, and then used that same key to get access to gitolite (i.e., copied that same pubkey as YourName.pub and ran gitolite setup on it).

As a result, the same key appears twice in the authkeys file now, and since the ssh server will always use the first match, the second occurrence (which invokes gitolite) is ignored.

To fix this, you have to use a different keypair for gitolite access. The best way to do this is to create a new keypair, copy the pubkey to the server as YourName.pub, then run gitolite setup -pk YourName.pub on the server. Remember to adjust your agent identities using ssh-add -D and ssh-add if you're using ssh-agent, otherwise these new keys may not work.

#stsapp3 appendix 3: ssh client may not be offering the right key

Make sure the right private key is being offered. Run ssh in very verbose mode and look for the word "Offering", like so:
```
ssh -vvv user@host pwd 2> >(grep -i offer)
```
If some keys are being offered, but not the key that was supposed to be used, you may be using ssh-agent (next bullet). You may also need to create some host aliases in ~/.ssh/config ([appendix 4][ssh-ha]).
(ssh-agent issues) If ssh-add -l responds with either "The agent has no identities." or "Could not open a connection to your authentication agent.", then you can skip this bullet.

However, if ssh-add -l lists any keys at all, then something weird happens. Due to a quirk in ssh-agent, ssh will now only use one of those keys, even if you explicitly ask for some other key to be used.

In that case, add the key you want using ssh-add ~/.ssh/YourName and try the access again.

#ssh-ha appendix 4: ssh host aliases

(or "making git use the right options for ssh")

The ssh command has several options for non-default items to be specified. Two common examples are -p for the port number if it is not 22, and -i for the public key file if you do not want to use just ~/.ssh/id_rsa or such.

Git has two ssh-based URL syntaxes, but neither allows specifying a non-default public key file. And a port number is only allowed in one of them. (See man git-clone for details). Finally, hosts often have to be referred with IP addresses (such is life), or the name is very long, or hard to remember.

Using a "host" para in ~/.ssh/config lets you nicely encapsulate all this within ssh and give it a short, easy-to-remember, name. Example:

host gitolite
    user git
    hostname a.long.server.name.or.annoying.IP.address
    port 22
    identityfile ~/.ssh/id_rsa

Now you can simply use the one word gitolite (which is the host alias we defined here) and ssh will infer all those details defined under it -- just say ssh gitolite and git clone gitolite:reponame and things will work.

(By the way, the 'port' and 'identityfile' lines are needed only if you have non-default values, although I put them in anyway just to be complete).

If you have more than one pubkey with access to the same server, you must use this method to make git pick up the right key. There is no other way to do this, as far as I know.

#ybpfail appendix 5: why bypassing gitolite causes a problem

When you bypass gitolite, you end up running your normal shell instead of the special gitolite entry point script gitolite-shell.

This means commands (like 'info') are interpreted by the shell instead of gitolite.

It also means git operations look for repos in $HOME.

However, gitolite places all your repos in a subdirectory pointed to by $REPO_BASE in the rc file (default: repositories), and internally prefixes this before calling the actual git command you invoked. Thus, the pathname of the repo that you use on the client is almost never the correct pathname on the server. (This is by design. Don't argue...)

This means that, you get 2 kinds of errors if you bypass gitolite

When you use git@server:reponame with a key that bypasses gitolite (i.e., gets you a shell), this prefixing does not happen, and so the repo is not found. Neither a clone/fetch nor a push will work.
Conversely, consider git@server:repositories/reponame.git. The clone operation will work -- you're using the full Unix path, (assuming default $REPO_BASE setting), and so the shell finds the repo where you said it would be. However, when you push, gitolite's update hook kicks in, and fails to run because some of the environment variables it is expecting are not present.

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