Difference between pages "Keychain" and "Repository Configuration"

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(Undo revision 9202 by Duncan.britton (talk))
 
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{{Article
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{{Warning|This article is a work-in-progress referring to a future Portage version. It does not apply to the current Funtoo Portage version. Please do not update your configuration yet.}}
|Author=Drobbins
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}}
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== Introduction ==
+
  
<tt>Keychain</tt> helps you to manage SSH and GPG keys in a convenient and secure manner. It acts as a frontend to <tt>ssh-agent</tt> and <tt>ssh-add</tt>, but allows you to easily have one long running <tt>ssh-agent</tt> process per system, rather than the norm of one <tt>ssh-agent</tt> per login session.
+
Starting with Portage-2.3.8, a switch to a new repository configuration framework is complete and users may want to update their configuration files. This document aims to describe the goals for the new framework and how to use it.
__TOC__
+
This dramatically reduces the number of times you need to enter your passphrase. With <tt>keychain</tt>, you only need to enter a passphrase once every time your local machine is rebooted. <tt>Keychain</tt> also makes it easy for remote cron jobs to securely &quot;hook in&quot; to a long running <tt>ssh-agent</tt> process, allowing your scripts to take advantage of key-based logins.
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{{#seo:
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|title=Keychain (SSH/GPG Key Management)
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|keywords=keychain,ssh,gpg,funtoo,linux,gentoo,Daniel Robbins
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|description=Keychain is a shell script that helps you to manage your SSH and GPG keys more easily.
+
}}
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== Download and Resources ==
+
  
The latest release of keychain is version <tt>2.7.2_beta1</tt>, and was released on July 7, 2014. The current version of keychain supports <tt>gpg-agent</tt> as well as <tt>ssh-agent</tt>.
+
== Multiple repository layout ==
 +
One of the most important changes is the switch from the old ''overlay'' layout to a new cleaner ''repository'' system. The new layout is more flexible and more predictable. For example, repositories can now use resources (eclasses, for example) provided by other repositories.
  
Keychain is compatible with many operating systems, including <tt>AIX</tt>, <tt>*BSD</tt>, <tt>Cygwin</tt>, <tt>MacOS X</tt>, <tt>Linux</tt>, <tt>HP/UX</tt>, <tt>Tru64 UNIX</tt>, <tt>IRIX</tt>, <tt>Solaris</tt> and <tt>GNU Hurd</tt>.
+
The old layout was based on the concept of one ''main tree'' and optionally a number of overlays. The main tree provided base system ebuilds, eclasses, profiles, while overlays mostly were able to provide their own ebuilds. The ebuild provided by overlays overrode the ebuilds in main tree to the extend of making it impossible to install the main tree version. Overlays could also provide eclasses for their own ebuilds and package.* entries that applied to all overlays and to the main tree. The Package Manager is responsible for updating the main tree, while overlays are managed externally.
  
=== Download ===
+
The new layout is based on the concept of one or more configurable repositories. Each repository can either be stand-alone or depend upon other repositories. The distribution provides a repository called ''funtoo'' (a drop-in replacement for Gentoo's ''gentoo'' repository). Users can install more repositories at they will, the repositories providing their own ebuilds, eclasses and profiles as necessary and/or using them from other repositories. Users can explicitly choose the repository they want to install packages from. The Package Manager can update all repositories.
  
* ''Release Archive''
+
== Portage configuration ==
** [http://www.funtoo.org/distfiles/keychain/keychain-2.7.2_beta1.tar.bz2 keychain 2.7.2_beta1]
+
=== New repository layout ===
** [http://www.funtoo.org/distfiles/keychain/keychain-2.7.1.tar.bz2 keychain 2.7.1]
+
The repository configuration should be stored in <code>/etc/portage/repos.conf</code>. It can be either a single file or a directory containing one or more ''.conf'' files.
  
* ''Apple MacOS X Packages''
+
The default configuration is installed as <code>/usr/share/portage/config/repos.conf</code>. This file is internal configuration file installed with portage ebuild and should '''not''' be modified. Instead, the configuration in <code>/etc/portage/repos.conf</code> can override the defaults specified there.
** [http://www.funtoo.org/distfiles/keychain/keychain-2.7.1-macosx.tar.gz keychain 2.7.1 MacOS X package]
+
  
Keychain development sources can be found in the [http://www.github.com/funtoo/keychain keychain git repository]. Please use the [https://bugs.funtoo.org Funtoo Linux bug tracker] and [irc://irc.freenode.net/funtoo #funtoo irc channel] for keychain support questions as well as bug reports.
+
The configuration uses format similar to Windows .ini files. Each section heading (repository name in square brackets) signifies a single repository, followed by one or more key-value option pairs. For example, the following file copies default configuration for Funtoo repository:
  
=== Project History ===
+
{{file|name=/etc/portage/repos.conf/funtoo.conf|desc=Example configuration override for Funtoo repository to move it to non-standard location|body=
 
+
[funtoo]
Daniel Robbins originally wrote <tt>keychain</tt> 1.0 through 2.0.3. 1.0 was written around June 2001, and 2.0.3 was released in late August, 2002.
+
# moved to non-standard location!
 
+
location = /var/db/repos/funtoo
After 2.0.3, <tt>keychain</tt> was maintained by various Gentoo developers, including Seth Chandler, Mike Frysinger and Robin H. Johnson, through July 3, 2003.
+
sync-type = git
 
+
sync-uri = git://github.com/funtoo/ports-2015.git
On April 21, 2004, Aron Griffis committed a major rewrite of <tt>keychain</tt> which was released as 2.2.0. Aron continued to actively maintain and improve <tt>keychain</tt> through October 2006 and the <tt>keychain</tt> 2.6.8 release. He also made a few commits after that date, up through mid-July, 2007. At this point, <tt>keychain</tt> had reached a point of maturity.
+
auto-sync = yes
 
+
In mid-July, 2009, Daniel Robbins migrated Aron's mercurial repository to git and set up a new project page on funtoo.org, and made a few bug fix commits to the git repo that had been collecting in [http://bugs.gentoo.org bugs.gentoo.org]. Daniel continues to maintain <tt>keychain</tt> and supporting documentation on funtoo.org, and plans to make regular maintenance releases of <tt>keychain</tt> as needed.
+
 
+
== Quick Setup ==
+
 
+
=== Linux ===
+
 
+
To install under Gentoo or Funtoo Linux, type
+
<console>
+
###i## emerge keychain
+
</console>
+
 
+
For other Linux distributions, use your distribution's package manager, or download and install using the source tarball above. Then generate RSA/DSA keys if necessary. The quick install docs assume you have a DSA key pair named <tt>id_dsa</tt> and <tt>id_dsa.pub</tt> in your <tt>~/.ssh/</tt> directory. Add the following to your <tt>~/.bash_profile</tt>:
+
 
+
{{file|name=~/.bash_profile|body=
+
eval `keychain --eval --agents ssh id_rsa`
+
 
}}
 
}}
  
If you want to take advantage of GPG functionality, ensure that GNU Privacy Guard is installed and omit the <tt>--agents ssh</tt> option above.
+
The most useful repository configuration options are listed below:
 +
;location: ''Obligatory.'' Specifies the directory where repository is/will be stored. If Portage knows how to sync the repository and the location does not exist, it will be created on next ''emerge --sync''. Otherwise, the directory must exist.
 +
;priority: Specifies the priority used for ordering ebuilds from different repositories. If two repositories provide an ebuild with matching versions, the repository with higher priority will be used.
 +
;auto-sync: Specifies whether ''emerge --sync'' should update the repository. Defaults to ''yes'' if ''sync-type'' is specified, ''no'' otherwise.
 +
;sync-depth: Specifies ''--depth'' for git clone. Used only on initial sync. Defaults to 1. Can be set to 0 to force full clone (not pass ''--depth'' at all).
 +
;sync-type: Specifies syncing/update method. Can be one of: ''cvs'', ''git'', ''rsync'', ''svn''.
 +
;sync-umask: Specifies the umask used when updating/syncing the repository.
 +
;sync-uri: Specifies remote URI from which the repository will be cloned/synced. Can use any syntax valid for a particular syncing method.
 +
;sync-user: Specifies the user[:group] used to update/sync the repository. If ''FEATURES=usersync'' is used, defaults to the credentials of directory owner.
  
=== Apple MacOS X ===
+
Additionally a <code>[DEFAULT]</code> section may be specified. Options in this section are used as defaults for all repositories.
  
To install under MacOS X, install the MacOS X package for keychain. Assuming you have an <tt>id_dsa</tt> and <tt>id_dsa.pub</tt> key pair in your <tt>~/.ssh/</tt> directory, add the following to your <tt>~/.bash_profile</tt>:
+
=== Migrating existing configurations ===
 
+
The new configuration format provides replacement for existing configuration done through <code>/etc/portage/make.conf</code> and environment variables. While the variables are still supported for backwards compatibility, users are recommended to move to the new configuration scheme. Funtoo portage ebuild is planned to make the migration unattended (repos.conf installed automatically to ease the config steps) with the following file:
{{file|name=~/.bash_profile|body=
+
eval `keychain --eval --agents ssh --inherit any id_dsa`
+
{{file|name=/etc/portage/repos.conf/funtoo.conf|body=
 +
[funtoo]
 +
location = /usr/portage
 +
sync-type = git
 +
sync-uri = git://github.com/funtoo/ports-2015.git
 +
auto-sync = yes
 
}}
 
}}
 +
The following replacements are provided for existing variables:
 +
;PORTDIR: Used to specify main tree location. Replaced by ''location'' key in the section corresponding to the default repository (<code>[funtoo]</code> by default).
 +
;PORTDIR_OVERLAY: Used to specify locations of overlays. Each of the paths needs to be replaced with a separate repository section, with the path placed in ''location'' key. Additionally, ''priority'' may be used to force specific ordering of ebuild overrides.
 +
;SYNC: Used to specify URI for syncing the main repository, also implied a protocol for doing that. Replaced by the ''sync-uri'' and ''sync-type'' keys in the default repository section.
 +
;SYNC_UMASK: Used to specify umask for syncing repositories. Replaced by ''sync-umask'' key in repository configuration. Can be specified in <code>[DEFAULT]</code> section to apply to all repositories.
 +
;SYNC_USER: Used to specify user credentials for syncing repositories. Replaced by ''sync-user'' key in repository configuration. Can be specified in <code>[DEFAULT]</code> section to apply to all repositories.
  
{{Fancynote|The <tt>--inherit any</tt> option above causes keychain to inherit any ssh key passphrases stored in your Apple MacOS Keychain. If you would prefer for this to not happen, then this option can be omitted.}}
+
{{file|name=/etc/portage/make.conf|desc=Example old make.conf file|body=
 +
# user changed PORTDIR location
 +
PORTDIR="/var/db/repos/funtoo"
 +
PORTDIR_OVERLAY="/var/db/repos/foo /var/db/repos/bar"
  
== Background ==
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SYNC="git://github.com/funtoo/ports-2015.git"
 
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SYNC_USER="oleg"
You're probably familiar with <tt>ssh</tt>, which has become a secure replacement for the venerable <tt>telnet</tt> and <tt>rsh</tt> commands.
+
SYNC_UMASK="022"
 
+
Typically, when one uses <tt>ssh</tt> to connect to a remote system, one supplies a secret passphrase to <tt>ssh</tt>, which is then passed in encrypted form over the network to the remote server. This passphrase is used by the remote <tt>sshd</tt> server to determine if you should be granted access to the system.
+
 
+
However, OpenSSH and nearly all other SSH clients and servers have the ability to perform another type of authentication, called asymmetric public key authentication, using the RSA or DSA authentication algorithms. They are very useful, but can also be complicated to use. <tt>keychain</tt> has been designed to make it easy to take advantage of the benefits of RSA and DSA authentication.
+
 
+
== Generating a Key Pair ==
+
 
+
To use RSA and DSA authentication, first you use a program called <tt>ssh-keygen</tt> (included with OpenSSH) to generate a ''key pair'' -- two small files. One of the files is the ''public key''. The other small file contains the ''private key''. <tt>ssh-keygen</tt> will ask you for a passphrase, and this passphrase will be used to encrypt your private key. You will need to supply this passphrase to use your private key. If you wanted to generate a DSA key pair, you would do this:
+
 
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<console># ##i##ssh-keygen -t dsa
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Generating public/private dsa key pair.</console>
+
You would then be prompted for a location to store your key pair. If you do not have one currently stored in <tt>~/.ssh</tt>, it is fine to accept the default location:
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+
<console>Enter file in which to save the key (/root/.ssh/id_dsa): </console>
+
Then, you are prompted for a passphrase. This passphrase is used to encrypt the ''private key'' on disk, so even if it is stolen, it will be difficult for someone else to use it to successfully authenticate as you with any accounts that have been configured to recognize your public key.
+
 
+
Note that conversely, if you '''do not''' provide a passphrase for your private key file, then your private key file '''will not''' be encrypted. This means that if someone steals your private key file, ''they will have the full ability to authenticate with any remote accounts that are set up with your public key.''
+
 
+
Below, I have supplied a passphrase so that my private key file will be encrypted on disk:
+
 
+
<console>Enter passphrase (empty for no passphrase): ##i#########
+
Enter same passphrase again: ##i#########
+
Your identification has been saved in /var/tmp/id_dsa.
+
Your public key has been saved in /var/tmp/id_dsa.pub.
+
The key fingerprint is:
+
5c:13:ff:46:7d:b3:bf:0e:37:1e:5e:8c:7b:a3:88:f4 root@devbox-ve
+
The key's randomart image is:
+
+--[ DSA 1024]----+
+
|          .     |
+
|          o  . |
+
|          o . ..o|
+
|      . . . o  +|
+
|        S    o. |
+
|            . o.|
+
|        .  ..++|
+
|        . o . =o*|
+
|        . E .+*.|
+
+-----------------+</console>
+
 
+
== Setting up Authentication ==
+
 
+
Here's how you use these files to authenticate with a remote server. On the remote server, you would append the contents of your ''public key'' to the <tt>~.ssh/authorized_keys</tt> file, if such a file exists. If it doesn't exist, you can simply create a new <tt>authorized_keys</tt> file in the remote account's <tt>~/.ssh</tt> directory that contains the contents of your local <tt>id_dsa.pub</tt> file.
+
 
+
Then, if you weren't going to use <tt>keychain</tt>, you'd perform the following steps. On your local client, you would start a program called <tt>ssh-agent</tt>, which runs in the background. Then you would use a program called <tt>ssh-add</tt> to tell <tt>ssh-agent</tt> about your secret private key. Then, if you've set up your environment properly, the next time you run <tt>ssh</tt>, it will find <tt>ssh-agent</tt> running, grab the private key that you added to <tt>ssh-agent</tt> using <tt>ssh-add</tt>, and use this key to authenticate with the remote server.
+
 
+
Again, the steps in the previous paragraph is what you'd do if <tt>keychain</tt> wasn't around to help. If you are using <tt>keychain</tt>, and I hope you are, you would simply add the following line to your <tt>~/.bash_profile</tt> or if a regular user to<tt>~/.bashrc</tt> :
+
 
+
{{file|name=~/.bash_profile|body=
+
eval `keychain --eval id_dsa`
+
 
}}
 
}}
  
The next time you log in or source your <tt>~/.bash_profile</tt> or if you use <tt>~/.bashrc</tt>, <tt>keychain</tt> will start, start <tt>ssh-agent</tt> for you if it has not yet been started, use <tt>ssh-add</tt> to add your <tt>id_dsa</tt> private key file to <tt>ssh-agent</tt>, and set up your shell environment so that <tt>ssh</tt> will be able to find <tt>ssh-agent</tt>. If <tt>ssh-agent</tt> is already running, <tt>keychain</tt> will ensure that your <tt>id_dsa</tt> private key has been added to <tt>ssh-agent</tt> and then set up your environment so that <tt>ssh</tt> can find the already-running <tt>ssh-agent</tt>. It will look something like this:
+
{{file|name=/etc/portage/repos.conf|desc=Replacement repos.conf file|body=
 +
[DEFAULT]
 +
sync-user = oleg
 +
sync-umask = 022
  
Note that when <tt>keychain</tt> runs for the first time after your local system has booted, you will be prompted for a passphrase for your private key file if it is encrypted. But here's the nice thing about using <tt>keychain</tt> -- even if you are using an encrypted private key file, you will only need to enter your passphrase when your system first boots (or in the case of a server, when you first log in.) After that, <tt>ssh-agent</tt> is already running and has your decrypted private key cached in memory. So if you open a new shell, you will see something like this:
+
[funtoo]
 +
location = /var/db/repos/funtoo
 +
sync-type = git
 +
sync-uri = git://github.com/funtoo/ports-2015.git
  
This means that you can now <tt>ssh</tt> to your heart's content, without supplying a passphrase.
+
[foo]
 +
location = /var/db/repos/foo
 +
priority = 1
  
You can also execute batch <tt>cron</tt> jobs and scripts that need to use <tt>ssh</tt> or <tt>scp</tt>, and they can take advantage of passwordless RSA/DSA authentication as well. To do this, you would add the following line to the top of a bash script:
+
[bar]
 
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location = /var/db/repos/bar
{{file|name=example-script.sh|body=
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priority = 2
eval `keychain --noask --eval id_dsa` || exit 1
+
 
}}
 
}}
  
The extra <tt>--noask</tt> option tells <tt>keychain</tt> that it should not prompt for a passphrase if one is needed. Since it is not running interactively, it is better for the script to fail if the decrypted private key isn't cached in memory via <tt>ssh-agent</tt>.
+
The <code>repos.conf</code> configuration can be further extended with ''sync-type'' and ''sync-uri'' for overlays to get ''emerge --sync'' updating them automatically.
  
== Keychain Options ==
+
let's see a real example of tree and overlays added.
 +
{{file|name=/etc/portage/repos.conf|desc=Replacement repos.conf file|body=
  
=== Specifying Agents ===
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[gentoo]
 
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location = /usr/portage
In the images above, you will note that <tt>keychain</tt> starts <tt>ssh-agent</tt>, but also starts <tt>gpg-agent</tt>. Modern versions of <tt>keychain</tt> also support caching decrypted GPG keys via use of <tt>gpg-agent</tt>, and will start <tt>gpg-agent</tt> by default if it is available on your system. To avoid this behavior and only start <tt>ssh-agent</tt>, modify your <tt>~/.bash_profile</tt> as follows:
+
sync-type = git
 
+
sync-uri = git://github.com/funtoo/ports-2012.git
{{file|name=~/.bash_profile|body=
+
eval `keychain --agents ssh --eval id_dsa` || exit 1
+
[funtoo-overlay]
 +
location = /root/git/funtoo-overlay
 +
 +
[funtoo-gnome]
 +
location = /root/git/funtoo-gnome-overlay
 
}}
 
}}
 
+
funtoo-overlay and funtoo-gnome-overlay are an overlays added on top of regular portage tree.
The additional <tt>--agents ssh</tt> option tells <tt>keychain</tt> just to manage <tt>ssh-agent</tt>, and ignore <tt>gpg-agent</tt> even if it is available.
+
[[Category:Portage]]
 
+
=== Clearing Keys ===
+
 
+
Sometimes, it might be necessary to flush all cached keys in memory. To do this, type:
+
 
+
<console># ##i##keychain --clear</console>
+
Any agent(s) will continue to run.
+
 
+
=== Improving Security ===
+
 
+
To improve the security of <tt>keychain</tt>, some people add the <tt>--clear</tt> option to their <tt>~/.bash_profile</tt> <tt>keychain</tt> invocation. The rationale behind this is that any user logging in should be assumed to be an intruder until proven otherwise. This means that you will need to re-enter any passphrases when you log in, but cron jobs will still be able to run when you log out.
+
 
+
=== Stopping Agents ===
+
 
+
If you want to stop all agents, which will also of course cause your keys/identities to be flushed from memory, you can do this as follows:
+
 
+
<console># ##i##keychain -k all</console>
+
If you have other agents running under your user account, you can also tell <tt>keychain</tt> to just stop only the agents that <tt>keychain</tt> started:
+
 
+
<console># ##i##keychain -k mine</console>
+
 
+
=== GPG ===
+
 
+
Keychain can ask you for your GPG passphrase if you provide it the GPG key ID. To find it out:
+
<console>
+
$##i## gpg -k
+
pub  2048R/DEADBEEF 2012-08-16
+
uid                  Name (Comment) <email@host.tld>
+
sub  2048R/86D2FAC6 2012-08-16
+
</console>
+
 
+
Note the '''DEADBEEF''' above is the ID. Then, in your login script, do your usual
+
 
+
<console>
+
$##i## keychain --dir ~/.ssh/.keychain ~/.ssh/id_rsa DEADBEEF
+
$##i## source ~/.ssh/.keychain/$HOST-sh
+
$##i## source ~/.ssh/.keychain/$HOST-sh-gpg
+
</console>
+
 
+
=== Learning More ===
+
 
+
The instructions above will work on any system that uses <tt>bash</tt> as its default shell, such as most Linux systems and Mac OS X.
+
 
+
To learn more about the many things that <tt>keychain</tt> can do, including alternate shell support, consult the keychain man page, or type <tt>keychain --help | less</tt> for a full list of command options.
+
 
+
I also recommend you read my original series of articles about [http://www.openssh.com OpenSSH] that I wrote for IBM developerWorks, called <tt>OpenSSH Key Management</tt>. Please note that <tt>keychain</tt> 1.0 was released along with Part 2 of this article, which was written in 2001. <tt>keychain</tt> has changed quite a bit since then. In other words, read these articles for the conceptual and [http://www.openssh.com OpenSSH] information, but consult the <tt>keychain</tt> man page for command-line options and usage instructions :)
+
 
+
* [http://www.ibm.com/developerworks/library/l-keyc.html Common Threads: OpenSSH key management, Part 1] - Understanding RSA/DSA Authentication
+
* [http://www.ibm.com/developerworks/library/l-keyc2/ Common Threads: OpenSSH key management, Part 2] - Introducing <tt>ssh-agent</tt> and <tt>keychain</tt>
+
* [http://www.ibm.com/developerworks/library/l-keyc3/ Common Threads: OpenSSH key management, Part 3] - Agent forwarding and <tt>keychain</tt> improvements
+
 
+
As mentioned at the top of the page, <tt>keychain</tt> development sources can be found in the [http://www.github.com/funtoo/keychain keychain git repository]. Please use the [http://groups.google.com/group/funtoo-dev funtoo-dev mailing list] and [irc://irc.freenode.net/funtoo #funtoo irc channel] for keychain support questions as well as bug reports.
+
 
+
[[Category:HOWTO]]
+
[[Category:Projects]]
+
[[Category:First Steps]]
+
[[Category:Articles]]
+
{{ArticleFooter}}
+

Revision as of 04:52, February 27, 2015

Warning

This article is a work-in-progress referring to a future Portage version. It does not apply to the current Funtoo Portage version. Please do not update your configuration yet.

Starting with Portage-2.3.8, a switch to a new repository configuration framework is complete and users may want to update their configuration files. This document aims to describe the goals for the new framework and how to use it.

Multiple repository layout

One of the most important changes is the switch from the old overlay layout to a new cleaner repository system. The new layout is more flexible and more predictable. For example, repositories can now use resources (eclasses, for example) provided by other repositories.

The old layout was based on the concept of one main tree and optionally a number of overlays. The main tree provided base system ebuilds, eclasses, profiles, while overlays mostly were able to provide their own ebuilds. The ebuild provided by overlays overrode the ebuilds in main tree to the extend of making it impossible to install the main tree version. Overlays could also provide eclasses for their own ebuilds and package.* entries that applied to all overlays and to the main tree. The Package Manager is responsible for updating the main tree, while overlays are managed externally.

The new layout is based on the concept of one or more configurable repositories. Each repository can either be stand-alone or depend upon other repositories. The distribution provides a repository called funtoo (a drop-in replacement for Gentoo's gentoo repository). Users can install more repositories at they will, the repositories providing their own ebuilds, eclasses and profiles as necessary and/or using them from other repositories. Users can explicitly choose the repository they want to install packages from. The Package Manager can update all repositories.

Portage configuration

New repository layout

The repository configuration should be stored in /etc/portage/repos.conf. It can be either a single file or a directory containing one or more .conf files.

The default configuration is installed as /usr/share/portage/config/repos.conf. This file is internal configuration file installed with portage ebuild and should not be modified. Instead, the configuration in /etc/portage/repos.conf can override the defaults specified there.

The configuration uses format similar to Windows .ini files. Each section heading (repository name in square brackets) signifies a single repository, followed by one or more key-value option pairs. For example, the following file copies default configuration for Funtoo repository:

/etc/portage/repos.conf/funtoo.conf - Example configuration override for Funtoo repository to move it to non-standard location
[funtoo]
# moved to non-standard location!
location = /var/db/repos/funtoo
sync-type = git
sync-uri = git://github.com/funtoo/ports-2015.git
auto-sync = yes

The most useful repository configuration options are listed below:

location
Obligatory. Specifies the directory where repository is/will be stored. If Portage knows how to sync the repository and the location does not exist, it will be created on next emerge --sync. Otherwise, the directory must exist.
priority
Specifies the priority used for ordering ebuilds from different repositories. If two repositories provide an ebuild with matching versions, the repository with higher priority will be used.
auto-sync
Specifies whether emerge --sync should update the repository. Defaults to yes if sync-type is specified, no otherwise.
sync-depth
Specifies --depth for git clone. Used only on initial sync. Defaults to 1. Can be set to 0 to force full clone (not pass --depth at all).
sync-type
Specifies syncing/update method. Can be one of: cvs, git, rsync, svn.
sync-umask
Specifies the umask used when updating/syncing the repository.
sync-uri
Specifies remote URI from which the repository will be cloned/synced. Can use any syntax valid for a particular syncing method.
sync-user
Specifies the user[:group] used to update/sync the repository. If FEATURES=usersync is used, defaults to the credentials of directory owner.

Additionally a [DEFAULT] section may be specified. Options in this section are used as defaults for all repositories.

Migrating existing configurations

The new configuration format provides replacement for existing configuration done through /etc/portage/make.conf and environment variables. While the variables are still supported for backwards compatibility, users are recommended to move to the new configuration scheme. Funtoo portage ebuild is planned to make the migration unattended (repos.conf installed automatically to ease the config steps) with the following file:

/etc/portage/repos.conf/funtoo.conf
[funtoo]
location = /usr/portage
sync-type = git
sync-uri = git://github.com/funtoo/ports-2015.git
auto-sync = yes

The following replacements are provided for existing variables:

PORTDIR
Used to specify main tree location. Replaced by location key in the section corresponding to the default repository ([funtoo] by default).
PORTDIR_OVERLAY
Used to specify locations of overlays. Each of the paths needs to be replaced with a separate repository section, with the path placed in location key. Additionally, priority may be used to force specific ordering of ebuild overrides.
SYNC
Used to specify URI for syncing the main repository, also implied a protocol for doing that. Replaced by the sync-uri and sync-type keys in the default repository section.
SYNC_UMASK
Used to specify umask for syncing repositories. Replaced by sync-umask key in repository configuration. Can be specified in [DEFAULT] section to apply to all repositories.
SYNC_USER
Used to specify user credentials for syncing repositories. Replaced by sync-user key in repository configuration. Can be specified in [DEFAULT] section to apply to all repositories.
/etc/portage/make.conf - Example old make.conf file
# user changed PORTDIR location
PORTDIR="/var/db/repos/funtoo"
PORTDIR_OVERLAY="/var/db/repos/foo /var/db/repos/bar"

SYNC="git://github.com/funtoo/ports-2015.git"
SYNC_USER="oleg"
SYNC_UMASK="022"
/etc/portage/repos.conf - Replacement repos.conf file
[DEFAULT]
sync-user = oleg
sync-umask = 022

[funtoo]
location = /var/db/repos/funtoo
sync-type = git
sync-uri = git://github.com/funtoo/ports-2015.git

[foo]
location = /var/db/repos/foo
priority = 1

[bar]
location = /var/db/repos/bar
priority = 2

The repos.conf configuration can be further extended with sync-type and sync-uri for overlays to get emerge --sync updating them automatically.

let's see a real example of tree and overlays added.

/etc/portage/repos.conf - Replacement repos.conf file
[gentoo]
location = /usr/portage
sync-type = git
sync-uri = git://github.com/funtoo/ports-2012.git
 
[funtoo-overlay]
location = /root/git/funtoo-overlay
 
[funtoo-gnome]
location = /root/git/funtoo-gnome-overlay

funtoo-overlay and funtoo-gnome-overlay are an overlays added on top of regular portage tree.