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Use SSH keys to communicate with GitLab

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Git is a distributed version control system, which means you can work locally, then share or push your changes to a server. In this case, the server you push to is GitLab.

GitLab uses the SSH protocol to securely communicate with Git. When you use SSH keys to authenticate to the GitLab remote server, you don't need to supply your username and password each time.

What are SSH keys

SSH uses two keys, a public key and a private key.

  • The public key can be distributed.
  • The private key should be protected.

It is not possible to reveal confidential data by uploading your public key. When you need to copy or upload your SSH public key, make sure you do not accidentally copy or upload your private key instead.

You can use your private key to sign commits, which makes your use of GitLab and your data even more secure. This signature then can be verified by anyone using your public key.

For details, see Asymmetric cryptography, also known as public-key cryptography.

Prerequisites

To use SSH to communicate with GitLab, you need:

  • The OpenSSH client, which comes pre-installed on GNU/Linux, macOS, and Windows 10.
  • SSH version 6.5 or later. Earlier versions used an MD5 signature, which is not secure.

To view the version of SSH installed on your system, run ssh -V.

Supported SSH key types

To communicate with GitLab, you can use the following SSH key types:

Administrators can restrict which keys are permitted and their minimum lengths.

ED25519 SSH keys

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

OpenSSH 6.5 introduced ED25519 SSH keys in 2014, and they should be available on most operating systems.

ED25519_SK SSH keys

To use ED25519_SK SSH keys on GitLab, your local client and GitLab server must have OpenSSH 8.2 or later installed.

ECDSA_SK SSH keys

To use ECDSA_SK SSH keys on GitLab, your local client and GitLab server must have OpenSSH 8.2 or later installed.

RSA SSH keys

  • Maximum RSA key length changed in GitLab 16.3.

Available documentation suggests ED25519 is more secure than RSA.

If you use an RSA key, the US National Institute of Standards and Technology in Publication 800-57 Part 3 (PDF) recommends a key size of at least 2048 bits. Due to limitations in Go, RSA keys cannot exceed 8192 bits.

The default key size depends on your version of ssh-keygen. Review the man page for your installed ssh-keygen command for details.

See if you have an existing SSH key pair

Before you create a key pair, see if a key pair already exists.

  1. Go to your home directory.

  2. Go to the .ssh/ subdirectory. If the .ssh/ subdirectory doesn't exist, you are either not in the home directory, or you haven't used ssh before. In the latter case, you need to generate an SSH key pair.

  3. See if a file with one of the following formats exists:

    Algorithm Public key Private key
    ED25519 (preferred) id_ed25519.pub id_ed25519
    ED25519_SK id_ed25519_sk.pub id_ed25519_sk
    ECDSA_SK id_ecdsa_sk.pub id_ecdsa_sk
    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

Generate an SSH key pair

If you do not have an existing SSH key pair, generate a new one:

  1. Open a terminal.

  2. Run ssh-keygen -t followed by the key type and an optional comment. This comment is included in the .pub file that's created. You may want to use an email address for the comment.

    For example, for ED25519:

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

    For 2048-bit RSA:

    ssh-keygen -t rsa -b 2048 -C "<comment>"

  3. Press Enter. Output similar to the following is displayed:

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

  4. Accept the suggested filename and directory, unless you are generating a deploy key or want to save in a specific directory where you store other keys.

    You can also dedicate the SSH key pair to a specific host.

  5. Specify a passphrase:

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

    A confirmation is displayed, including information about where your files are stored.

A public and private key are generated. Add the public SSH key to your GitLab account and keep the private key secure.

Configure SSH to point to a different directory

If you did not save your SSH key pair in the default directory, configure your SSH client to point to the directory where the private key is stored.

  1. Open a terminal and run this command:

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

  2. Save these settings in the ~/.ssh/config file. For example:

    # 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

For more information on these settings, see the man ssh_config page in the SSH configuration manual.

Public SSH keys must be unique to GitLab because they bind to your account. Your SSH key is the only identifier you have when you push code with SSH. It must uniquely map to a single user.

Update your SSH key passphrase

You can update the passphrase for your SSH key:

  1. Open a terminal and run this command:

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

  2. At the prompts, enter the passphrase and then press Enter.

Upgrade your RSA key pair to a more secure format

If your version of OpenSSH is between 6.5 and 7.8, you can save your private RSA SSH keys in a more secure OpenSSH format by opening a terminal and running this 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 "<comment>"

Generate an SSH key pair for a FIDO2 hardware security key

To generate ED25519_SK or ECDSA_SK SSH keys, you must use OpenSSH 8.2 or later:

  1. Insert a hardware security key into your computer.

  2. Open a terminal.

  3. Run ssh-keygen -t followed by the key type and an optional comment. This comment is included in the .pub file that's created. You may want to use an email address for the comment.

    For example, for ED25519_SK:

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

    For ECDSA_SK:

    ssh-keygen -t ecdsa-sk -C "<comment>"

    If your security key supports FIDO2 resident keys, you can enable this when creating your SSH key:

    ssh-keygen -t ed25519-sk -O resident -C "<comment>"

    -O resident indicates that the key should be stored on the FIDO authenticator itself. Resident key is easier to import to a new computer because it can be loaded directly from the security key by ssh-add -K or ssh-keygen -K.

  4. Press Enter. Output similar to the following is displayed:

    Generating public/private ed25519-sk key pair.
You may need to touch your authenticator to authorize key generation.

  5. Touch the button on the hardware security key.

  6. Accept the suggested filename and directory:

    Enter file in which to save the key (/home/user/.ssh/id_ed25519_sk):

  7. Specify a passphrase:

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

    A confirmation is displayed, including information about where your files are stored.

A public and private key are generated. Add the public SSH key to your GitLab account.

Generate an SSH key pair with a password manager

Generate an SSH key pair with 1Password

You can use 1Password and the 1Password browser extension to either:

  • Automatically generate a new SSH key.
  • Use an existing SSH key in your 1Password vault to authenticate with GitLab.
  1. Sign in to GitLab.
  2. On the left sidebar, select your avatar.
  3. Select Edit profile.
  4. On the left sidebar, select SSH Keys.
  5. Select Add new key.
  6. Select Key, and you should see the 1Password helper appear.
  7. Select the 1Password icon and unlock 1Password.
  8. You can then select Create SSH Key or select an existing SSH key to fill in the public key.
  9. In the Title box, enter a description, like Work Laptop or Home Workstation.
  10. Optional. Select the Usage type of the key. It can be used either for Authentication or Signing or both. Authentication & Signing is the default value.
  11. Optional. Update Expiration date to modify the default expiration date.
  12. Select Add key.

For more information about using 1Password with SSH keys, see the 1Password documentation.

Add an SSH key to your GitLab account

  • Suggested default expiration date for keys introduced in GitLab 15.4.
  • Usage types for SSH keys added in GitLab 15.7.

To use SSH with GitLab, copy your public key to your GitLab account:

  1. Copy the contents of your public key file. You can do this manually or use a script. For example, to copy an ED25519 key to the clipboard:

    macOS

    tr -d '\n' < ~/.ssh/id_ed25519.pub | pbcopy

    Linux (requires the xclip package)

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

    Git Bash on Windows

    cat ~/.ssh/id_ed25519.pub | clip

    Replace id_ed25519.pub with your filename. For example, use id_rsa.pub for RSA.

  2. Sign in to GitLab.

  3. On the left sidebar, select your avatar.

  4. Select Edit profile.

  5. On the left sidebar, select SSH Keys.

  6. Select Add new key.

  7. In the Key box, paste the contents of your public key. If you manually copied the key, make sure you copy the entire key, which starts with ssh-rsa, ssh-dss, ecdsa-sha2-nistp256, ecdsa-sha2-nistp384, ecdsa-sha2-nistp521, ssh-ed25519, sk-ecdsa-sha2-nistp256@openssh.com, or sk-ssh-ed25519@openssh.com, and may end with a comment.

  8. In the Title box, type a description, like Work Laptop or Home Workstation.

  9. Optional. Select the Usage type of the key. It can be used either for Authentication or Signing or both. Authentication & Signing is the default value.

  10. Optional. Update Expiration date to modify the default expiration date.

    • Administrators can view expiration dates and use them for guidance when deleting keys.
    • GitLab checks all SSH keys at 01:00 AM UTC every day. It emails an expiration notice for all SSH keys that are scheduled to expire seven days from now.
    • GitLab checks all SSH keys at 02:00 AM UTC every day. It emails an expiration notice for all SSH keys that expire on the current date.

  11. Select Add key.

Verify that you can connect

Verify that your SSH key was added correctly.

The following commands use the example hostname gitlab.example.com. Replace this example hostname with your GitLab instance's hostname, for example, git@gitlab.com. By default, GitLab uses git username to authenticate. It can be different if it was changed by the administrator.

  1. To ensure you're connecting to the correct server, check the server's SSH host keys fingerprint. For:

    • GitLab.com, see the SSH host keys fingerprints documentation.
    • GitLab.com or another GitLab instance, see gitlab.example.com/help/instance_configuration#ssh-host-keys-fingerprints where gitlab.example.com is gitlab.com (for GitLab.com) or the address of the GitLab instance.

  2. Open a terminal and run this command, replacing gitlab.example.com with your GitLab instance URL:

    ssh -T git@gitlab.example.com

  3. If this is the first time you connect, you should verify the authenticity of the GitLab host. If you see a message like:

    The authenticity of host 'gitlab.example.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.example.com' (ECDSA) to the list of known hosts.

    Type yes and press Enter.

  4. Run the ssh -T git@gitlab.example.com command again. You should receive a Welcome to GitLab, @username! message.

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

ssh -Tvvv git@gitlab.example.com

Use different keys for different repositories

You can use a different key for each repository.

Open a terminal and run this command:

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

This command does not use the SSH Agent and requires Git 2.10 or later. For more information on ssh command options, see the man pages for both ssh and ssh_config.

View your account's SSH keys

To view the SSH keys for your account:

  1. On the left sidebar, select your avatar.
  2. Select Edit profile.
  3. On the left sidebar, select SSH Keys.

Your existing SSH keys are listed at the bottom of the page. The information includes:

  • The key's:
    • Name.
    • Public fingerprint.
    • Expiry date.
    • Permitted usage types.
  • The time a key was last used.

Delete an SSH key

To permanently delete an SSH key:

  1. On the left sidebar, select your avatar.
  2. Select Edit profile.
  3. On the left sidebar, select SSH Keys.
  4. Next to the key you want to delete, select Remove ({remove}).
  5. Select Delete.

Use different accounts on a single GitLab instance

You can use multiple accounts to connect to a single instance of GitLab. You can do this by using the command in the previous topic. However, even if you set IdentitiesOnly to yes, you cannot sign in if an IdentityFile exists outside of a Host block.

Instead, you can assign aliases to hosts in the ~/.ssh/config file.

  • For the Host, use an alias like user_1.gitlab.com and user_2.gitlab.com. Advanced configurations are more difficult to maintain, and these strings are easier to understand when you use tools like git remote.
  • For the IdentityFile, use the path the private key.
# 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>

Now, to clone a repository for user_1, use user_1.gitlab.com in the git clone command:

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

To update a previously-cloned repository that is aliased as origin:

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

NOTE: Private and public keys contain sensitive data. Ensure the permissions on the files make them readable to you but not accessible to others.

Configure two-factor authentication (2FA)

You can set up two-factor authentication (2FA) for Git over SSH. You should use ED25519_SK or ECDSA_SK SSH keys.

Use EGit on Eclipse

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

Use SSH on Microsoft Windows

If you're running Windows 10, you can either use the Windows Subsystem for Linux (WSL) with WSL 2 which has both git and ssh preinstalled, or install Git for Windows to use SSH through PowerShell.

The SSH key generated in WSL is not directly available for Git for Windows, and vice versa, as both have a different home directory:

  • WSL: /home/<user>
  • Git for Windows: C:\Users\<user>

You can either copy over the .ssh/ directory to use the same key, or generate a key in each environment.

If you're running Windows 11 and using OpenSSH for Windows, ensure the HOME environment variable is set correctly. Otherwise, your private SSH key might not be found.

Alternative tools include:

Overriding SSH settings on the GitLab server

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

SSH client operations performed on the GitLab server are executed as this user. You can modify this SSH configuration. For example, you can specify a private SSH key for this user to use for authentication requests. However, this practice is not supported and is strongly discouraged as it presents significant security risks.

GitLab checks for this condition, and directs you to this section if your server is configured this way. For example:

$ 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/user/ssh.md#overriding-ssh-settings-on-the-gitlab-server
  Please fix the error above and rerun the checks.

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

Verify GitLab SSH ownership and permissions

The GitLab SSH folder and files must have the following permissions:

  • The folder /var/opt/gitlab/.ssh/ must be owned by the git group and the git user, with permissions set to 700.
  • The authorized_keys file must have permissions set to 600.
  • The authorized_keys.lock file must have permissions set to 644.

To verify that these permissions are correct, run the following:

stat -c "%a %n" /var/opt/gitlab/.ssh/.

Set permissions

If the permissions are wrong, sign in to the application server and run:

cd /var/opt/gitlab/
chown git:git /var/opt/gitlab/.ssh/
chmod 700  /var/opt/gitlab/.ssh/
chmod 600  /var/opt/gitlab/.ssh/authorized_keys
chmod 644  /var/opt/gitlab/.ssh/authorized_keys.lock