gitlab-org--gitlab-foss/doc/ssh/README.md

type
howto, reference

GitLab and SSH keys

Git is a distributed version control system, which means you can work locally. In addition, you can also share or "push" your changes to other servers. GitLab supports secure communication between Git and its servers using SSH keys.

The SSH protocol provides this security and allows you to authenticate to the GitLab remote server without supplying your username or password each time.

This page can help you configure secure SSH keys which you can use to help secure connections to GitLab repositories.

• If you need information on creating SSH keys, start with our options for SSH keys.
• If you have SSH keys dedicated for your GitLab account, you may be interested in Working with non-default SSH key pair paths.
• If you already have an SSH key pair, you can go to how you can add an SSH key to your GitLab account.

Requirements

To support SSH, GitLab requires the installation of the OpenSSH client, which comes pre-installed on GNU/Linux and macOS, but not on Windows.

Make sure that your system includes SSH version 6.5 or newer, as that excludes the now insecure MD5 signature scheme. The following command returns the version of SSH installed on your system:

ssh -V

While GitLab does not support installation on Microsoft Windows, you can set up SSH keys to set up Windows as a client.

Options for SSH keys

GitLab supports the use of RSA, DSA, ECDSA, and ED25519 keys.

• GitLab has deprecated DSA keys in GitLab 11.0.
• As noted in Practical Cryptography With Go, the security issues related to DSA also apply to ECDSA.

TIP: Tip: Available documentation suggests that ED25519 is more secure. If you use an RSA key, the US National Institute of Science and Technology in Publication 800-57 Part 3 (PDF) recommends a key size of at least 2048 bits.

Therefore, our documentation focuses on the use of ED25519 and RSA keys.

Administrators can restrict which keys should be permitted and their minimum lengths.

Review existing SSH keys

If you have existing SSH keys, you may be able to use them to help secure connections with GitLab repositories. By default, SSH keys on Linux and macOS systems are stored in the user's home directory, in the .ssh/ subdirectory. The following table includes default filenames for each SSH key algorithm:

Algorithm	Public key	Private key
ED25519 (preferred)	id_ed25519.pub	id_ed25519
RSA (at least 2048-bit key size)	id_rsa.pub	id_rsa
DSA (deprecated)	id_dsa.pub	id_dsa
ECDSA	id_ecdsa.pub	id_ecdsa

For recommendations, see options for SSH keys.

Generating a new SSH key pair

If you want to create:

• An ED25519 key, read ED25519 SSH keys.
• An RSA key, read RSA SSH keys.

ED25519 SSH keys

The book Practical Cryptography With Go suggests that ED25519 keys are more secure and performant than RSA keys.

As OpenSSH 6.5 introduced ED25519 SSH keys in 2014, they should be available on any current operating system.

You can create and configure an ED25519 key with the following command:

ssh-keygen -t ed25519 -C "<comment>"

The -C flag, with a quoted comment such as an email address, is an optional way to label your SSH keys.

You'll see a response similar to:

Generating public/private ed25519 key pair.
Enter file in which to save the key (/home/user/.ssh/id_ed25519):

For guidance, proceed to the common steps.

RSA SSH keys

If you use RSA keys for SSH, the US National Institute of Standards and Technology recommends that you use a key size of at least 2048 bits. By default, the ssh-keygen command creates an 1024-bit RSA key.

You can create and configure an RSA key with the following command, substituting if desired for the minimum recommended key size of 2048:

ssh-keygen -t rsa -b 2048 -C "email@example.com"

The -C flag, with a quoted comment such as an email address, is an optional way to label your SSH keys.

You'll see a response similar to:

Generating public/private rsa key pair.
Enter file in which to save the key (/home/user/.ssh/id_rsa):

For guidance, proceed to the common steps.

NOTE: Note: If you have OpenSSH version 7.8 or below, consider the problems associated with encoding.

Common steps for generating an SSH key pair

Whether you're creating a ED25519 or an RSA key, you've started with the ssh-keygen command. At this point, you'll see the following message in the command line (for ED25519 keys):

Generating public/private ed25519 key pair.
Enter file in which to save the key (/home/user/.ssh/id_rsa):

If you don't already have an SSH key pair and are not generating a deploy key, accept the suggested file and directory. Your SSH client will use the resulting SSH key pair with no additional configuration.

Alternatively, you can save the new SSH key pair in a different location. You can assign the directory and file name of your choice. You can also dedicate that SSH key pair to a specific host.

After assigning a file to save your SSH key, you'll get a chance to set up a passphrase for your SSH key:

Enter passphrase (empty for no passphrase):
Enter same passphrase again:

If successful, you'll see confirmation of where the ssh-keygen command saved your identification and private key.

When needed, you can update the passphrase with the following command:

ssh-keygen -p -f /path/to/ssh_key

RSA keys and OpenSSH from versions 6.5 to 7.8

Before OpenSSH 7.8, the default public key fingerprint for RSA keys was based on MD5, and is therefore insecure.

If your version of OpenSSH lies between version 6.5 to version 7.8 (inclusive), run ssh-keygen with the -o option to save your private SSH keys in the more secure OpenSSH format.

If you already have an RSA SSH key pair to use with GitLab, consider upgrading it to use the more secure password encryption format. You can do so with the following command:

ssh-keygen -o -f ~/.ssh/id_rsa

Alternatively, you can generate a new RSA key with the more secure encryption format with the following command:

ssh-keygen -o -t rsa -b 4096 -C "email@example.com"

NOTE: Note: As noted in the ssh-keygen man page, ED25519 already encrypts keys to the more secure OpenSSH format.

Adding an SSH key to your GitLab account

Now you can copy the SSH key you created to your GitLab account. To do so, follow these steps:

1. Copy your public SSH key to a location that saves information in text format. The following options saves information for ED25519 keys to the clipboard for the noted operating system:

   macOS:

   pbcopy < ~/.ssh/id_ed25519.pub
   

   Linux (requires the xclip package):

   xclip -sel clip < ~/.ssh/id_ed25519.pub
   

   Git Bash on Windows:

   cat ~/.ssh/id_ed25519.pub | clip
   

   If you're using an RSA key, substitute accordingly.

2. Navigate to http://gitlab.com and sign in.

3. Select your avatar in the upper right corner, and click Settings

4. Click SSH Keys.

5. Paste the public key that you copied into the Key text box.

6. Make sure your key includes a descriptive name in the Title text box, such as Work Laptop or Home Workstation.

7. Include an (optional) expiry date for the key under "Expires at" section. (Introduced in GitLab 12.9.)

8. Click the Add key button.

SSH keys that have "expired" using this procedure will still be valid in GitLab workflows. As the GitLab-configured expiration date is not included in the SSH key itself, you can still export public SSH keys as needed.

NOTE: Note: If you manually copied your public SSH key make sure you copied the entire key starting with ssh-ed25519 (or ssh-rsa) and ending with your email address.

Testing that everything is set up correctly

To test whether your SSH key was added correctly, run the following command in your terminal (replacing gitlab.com with your GitLab's instance domain):

ssh -T git@gitlab.com

The first time you connect to GitLab via SSH, you will be asked to verify the authenticity of the GitLab host that you're connecting to. For example, when connecting to GitLab.com, answer yes to add GitLab.com to the list of trusted hosts:

The authenticity of host 'gitlab.com (35.231.145.151)' can't be established.
ECDSA key fingerprint is SHA256:HbW3g8zUjNSksFbqTiUWPWg2Bq1x8xdGUrliXFzSnUw.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added 'gitlab.com' (ECDSA) to the list of known hosts.

NOTE: Note: For GitLab.com, consult the SSH host keys fingerprints, section to make sure you're connecting to the correct server. For example, you'll see the ECDSA key fingerprint shown above in the linked section.

Once added to the list of known hosts, you won't be asked to validate the authenticity of GitLab's host again. Run the above command once more, and you should only receive a Welcome to GitLab, @username! message.

If the welcome message doesn't appear, you can troubleshoot the problem by running ssh in verbose mode with the following command:

ssh -Tvvv git@gitlab.com

Working with non-default SSH key pair paths

If you used a non-default file path for your GitLab SSH key pair, configure your SSH client to point to your GitLab private SSH key.

To make these changes, run the following commands:

eval $(ssh-agent -s)
ssh-add <path to private SSH key>

Now save these settings to the ~/.ssh/config file. Two examples for SSH keys dedicated to GitLab are shown here:

# GitLab.com
Host gitlab.com
  Preferredauthentications publickey
  IdentityFile ~/.ssh/gitlab_com_rsa

# Private GitLab instance
Host gitlab.company.com
  Preferredauthentications publickey
  IdentityFile ~/.ssh/example_com_rsa

Public SSH keys need to be unique to GitLab, as they will bind to your account. Your SSH key is the only identifier you'll have when pushing code via SSH, that's why it needs to uniquely map to a single user.

Per-repository SSH keys

If you want to use different keys depending on the repository you are working on, you can issue the following command while inside your repository:

git config core.sshCommand "ssh -o IdentitiesOnly=yes -i ~/.ssh/private-key-filename-for-this-repository -F /dev/null"

This will not use the SSH Agent and requires at least Git 2.10.

Multiple accounts on a single GitLab instance

The per-repository method also works for using multiple accounts within a single GitLab instance.

Alternatively, it is possible to directly assign aliases to hosts in ~.ssh/config. SSH and, by extension, Git will fail to log in if there is an IdentityFile set outside of a Host block in .ssh/config. This is due to how SSH assembles IdentityFile entries and is not changed by setting IdentitiesOnly to yes. IdentityFile entries should point to the private key of an SSH key pair.

NOTE: Note: Private and public keys should be readable by the user only. Accomplish this on Linux and macOS by running: chmod 0400 ~/.ssh/<example_ssh_key> and chmod 0400 ~/.ssh/<example_sh_key.pub>.

# User1 Account Identity
Host <user_1.gitlab.com>
  Hostname gitlab.com
  PreferredAuthentications publickey
  IdentityFile ~/.ssh/<example_ssh_key1>

# User2 Account Identity
Host <user_2.gitlab.com>
  Hostname gitlab.com
  PreferredAuthentications publickey
  IdentityFile ~/.ssh/<example_ssh_key2>

NOTE: Note: The example Host aliases are defined as user_1.gitlab.com and user_2.gitlab.com for efficiency and transparency. Advanced configurations are more difficult to maintain; using this type of alias makes it easier to understand when using other tools such as git remote sub-commands. SSH would understand any string as a Host alias thus Tanuki1 and Tanuki2, despite giving very little context as to where they point, would also work.

Cloning the gitlab repository normally looks like this:

git clone git@gitlab.com:gitlab-org/gitlab.git

To clone it for user_1, replace gitlab.com with the SSH alias user_1.gitlab.com:

git clone git@<user_1.gitlab.com>:gitlab-org/gitlab.git

Fix a previously cloned repository using the git remote command.

The example below assumes the remote repository is aliased as origin.

git remote set-url origin git@<user_1.gitlab.com>:gitlab-org/gitlab.git

Deploy keys

Read the documentation on Deploy Keys.

Applications

Eclipse

If you are using EGit, you can add your SSH key to Eclipse.

SSH on the GitLab server

GitLab integrates with the system-installed SSH daemon, designating a user (typically named git) through which all access requests are handled. Users connecting to the GitLab server over SSH are identified by their SSH key instead of their username.

SSH client operations performed on the GitLab server will be executed as this user. Although it is possible to modify the SSH configuration for this user to, e.g., provide a private SSH key to authenticate these requests by, this practice is not supported and is strongly discouraged as it presents significant security risks.

The GitLab check process includes a check for this condition, and will direct you to this section if your server is configured like this, e.g.:

$ gitlab-rake gitlab:check

Git user has default SSH configuration? ... no
  Try fixing it:
  mkdir ~/gitlab-check-backup-1504540051
  sudo mv /var/lib/git/.ssh/id_rsa ~/gitlab-check-backup-1504540051
  sudo mv /var/lib/git/.ssh/id_rsa.pub ~/gitlab-check-backup-1504540051
  For more information see:
  doc/ssh/README.md in section "SSH on the GitLab server"
  Please fix the error above and rerun the checks.

Remove the custom configuration as soon as you're able to. These customizations are explicitly not supported and may stop working at any time.

Options for Microsoft Windows

If you're running Windows 10, the Windows Subsystem for Linux (WSL), and its latest WSL 2 version, support the installation of different Linux distributions, which include the Git and SSH clients.

For current versions of Windows, you can also install the Git and SSH clients with Git for Windows.

Alternative tools include:

• Cygwin
• PuttyGen

Troubleshooting

If on Git clone you are prompted for a password like git@gitlab.com's password: something is wrong with your SSH setup.

• Ensure that you generated your SSH key pair correctly and added the public SSH key to your GitLab profile
• Try manually registering your private SSH key using ssh-agent as documented earlier in this document
• Try to debug the connection by running ssh -Tv git@example.com (replacing example.com with your GitLab domain)