Sharing Mercurial repositories with mercurial-server

About mercurial-server
mercurial-server is software for Debian and Ubuntu systems which gives your developers remote read/write access to Mercurial repositories using SSH public key authentication; it provides convenient and fine-grained key management and access control.
mercurial-server is the easiest and most secure way for several developers to have read/write access to a central repository, but that's not the only way for several people to work on the same project using Mercurial; you should be familiar with the other ways of handling multiple commiters before deciding to use this.
Though mercurial-server is currently targeted at Debian-based systems such as Ubuntu, other users have reported success getting it running on other Unix-based systems such as Red Hat. Running it on a non-Unix system such as Windows is not supported. You will need root privileges to install it.

Legalese
This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.

Step by step
mercurial-server authenticates users not using passwords but using SSH public keys; everyone who wants access to a mercurial-server repository will need such a key, so you'll need to familiarize yourself with them before proceeding. In combination with ssh-agent (or equivalents such as the Windows program Pageant), this means that users will not need to type in a password to access the repository.
In what follows, we assume that you usually sit at a machine called my-workstation and you wish to install mercurial-server on repository-host. First, you'll need to create an SSH public key if you haven't already. You should consult your system documentation on how to do this, but it should look something like this.

user@my-workstation:~$ ssh-keygen
Generating public/private rsa key pair.
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /home/user/.ssh/id_rsa.
Your public key has been saved in /home/user/.ssh/id_rsa.pub.
The key fingerprint is:
8b:aa:0a:98:fe:e7:84:48:a3:fe:5f:31:4b:16:e6:0b user@my-workstation
user@my-workstation:~$ ssh-add
Enter passphrase for /home/user/.ssh/id_rsa: 
Identity added: /home/user/.ssh/id_rsa (/home/user/.ssh/id_rsa)
user@my-workstation:~$

Now copy the files you're going to need over to your target system, and install mercurial-server

user@my-workstation:~$ ssh-copy-id repository-host
user@repository-host's password:
Now try logging into the machine, with "ssh 'repository-host'", and check in:

  .ssh/authorized_keys

to make sure we haven't added extra keys that you weren't expecting.
user@my-workstation:~$ scp mercurial-server_0.6.1_amd64.deb repository-host:
mercurial-server_0.6.1_amd64.deb 100%
user@my-workstation:~$ ssh -A repository-host
user@repository-host:~$ sudo dpkg -i ../mercurial-server_0.6.1_amd64.deb
[sudo] password for user: 
Selecting previously deselected package mercurial-server.
(Reading database ... 144805 files and directories currently installed.)
Unpacking mercurial-server (from .../mercurial-server_0.6.1_amd64.deb) ...
Setting up mercurial-server (0.6.1) ...
user@repository-host:~$

mercurial-server is now installed on the repository host. Next, we need to give you permission to see its repositories.

user@repository-host:~$ ssh-add -L > my-key
user@repository-host:~$ sudo mkdir -p /etc/mercurial-server/keys/root/user
user@repository-host:~$ sudo cp my-key /etc/mercurial-server/keys/root/user/my-workstation
user@repository-host:~$ sudo -u hg /usr/share/mercurial-server/refresh-auth
user@repository-host:~$ exit
Connection to shell closed.
user@my-workstation:~$

You can now create repositories on the remote machine and have complete read-write access to all of them; you need never log on to repository-host again.

user@my-workstation:~$ cd my-mercurial-project
user@my-workstation:~/my-mercurial-project$ hg clone . ssh://hg@repository-host/repository/name
searching for changes
remote: adding changesets
remote: adding manifests
remote: adding file changes
remote: added 119 changesets with 284 changes to 61 files
user@my-workstation:~/my-mercurial-project$ hg pull ssh://hg@repository-host/repository/name
pulling from ssh://hg@repository-host/repository/name
searching for changes
no changes found
user@my-workstation:~/my-mercurial-project$

As things stand, no-one but you has any access to any repositories you create on this system. In order to give anyone else access, you'll need a copy of their SSH public key. Once you have that key, you could give them access by logging into repository-host, putting their keys in the right place under /etc/mercurial-server/keys, and re-running sudo -u hg /usr/share/mercurial-server/refresh-auth. However, there's a more convenient way.

user@my-workstation:~/my-mercurial-project$ cd ..
user@my-workstation:~$ hg clone ssh://hg@repository-host/hgadmin
destination directory: hgadmin
no changes found
updating working directory
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
user@my-workstation:~$ cd hgadmin
user@my-workstation:~/hgadmin$ mkdir -p keys/users/other-user
user@my-workstation:~/hgadmin$ cp ~/other-users-key.pub keys/users/other-user/their-workstation
user@my-workstation:~/hgadmin$ hg add
adding keys/users/other-user/their-workstation
user@my-workstation:~/hgadmin$ hg commit -m "Add other user"
user@my-workstation:~/hgadmin$ hg push
pushing to ssh://hg@repository-host/hgadmin
searching for changes
remote: adding changesets
remote: adding manifests
remote: adding file changes
remote: added 1 changesets with 1 changes to 1 files
user@my-workstation:~/hgadmin$

The new user can now read and write to your ssh://hg@repository-host/repository/name repository.