Use SSH keys to communicate with GitLab
Offering: GitLab.com, Self-managed, GitLab Dedicated
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:
- ED25519
- ED25519_SK (Available in GitLab 14.8 and later.)
- ECDSA_SK (Available in GitLab 14.8 and later.)
- RSA
- DSA (Deprecated in GitLab 11.0.)
- ECDSA (As noted in Practical Cryptography With Go, the security issues related to DSA also apply to ECDSA.)
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
- Introduced in GitLab 14.8.
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
- Introduced in GitLab 14.8.
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.
- Go to your home directory.
- Go to the
.ssh/
subdirectory. If the.ssh/
subdirectory doesn’t exist, you are either not in the home directory, or you haven’t usedssh
before. In the latter case, you need to generate an SSH key pair. -
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:
- Open a terminal.
-
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>"
-
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):
-
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.
-
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.
-
Open a terminal and run this command:
eval $(ssh-agent -s) ssh-add <directory to private SSH key>
-
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:
-
Open a terminal and run this command:
ssh-keygen -p -f /path/to/ssh_key
-
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:
- Insert a hardware security key into your computer.
- Open a terminal.
-
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 byssh-add -K
orssh-keygen -K
. -
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.
-
Touch the button on the hardware security key.
-
Accept the suggested filename and directory:
Enter file in which to save the key (/home/user/.ssh/id_ed25519_sk):
-
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.
- Sign in to GitLab.
- On the left sidebar, select your avatar.
- Select Edit profile.
- On the left sidebar, select SSH Keys.
- Select Add new key.
- Select Key, and you should see the 1Password helper appear.
- Select the 1Password icon and unlock 1Password.
- You can then select Create SSH Key or select an existing SSH key to fill in the public key.
- In the Title box, enter a description, like
Work Laptop
orHome Workstation
. - Optional. Select the Usage type of the key. It can be used either for
Authentication
orSigning
or both.Authentication & Signing
is the default value. - Optional. Update Expiration date to modify the default expiration date.
- 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:
-
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, useid_rsa.pub
for RSA. - Sign in to GitLab.
- On the left sidebar, select your avatar.
- Select Edit profile.
- On the left sidebar, select SSH Keys.
- Select Add new key.
- 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
, orsk-ssh-ed25519@openssh.com
, and may end with a comment. - In the Title box, type a description, like
Work Laptop
orHome Workstation
. - Optional. Select the Usage type of the key. It can be used either for
Authentication
orSigning
or both.Authentication & Signing
is the default value. - Optional. Update Expiration date to modify the default expiration date.
In:
- GitLab 13.12 and earlier, the expiration date is informational only. It doesn’t prevent you from using the key. Administrators can view expiration dates and use them for guidance when deleting keys.
- 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. (Introduced in GitLab 13.11.)
- 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. (Introduced in GitLab 13.11.)
- 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.
- 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
wheregitlab.example.com
isgitlab.com
(for GitLab.com) or the address of the GitLab instance.
-
Open a terminal and run this command, replacing
gitlab.example.com
with your GitLab instance URL:ssh -T git@gitlab.example.com
-
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. - 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:
- On the left sidebar, select your avatar.
- Select Edit profile.
- 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:
- On the left sidebar, select your avatar.
- Select Edit profile.
- On the left sidebar, select SSH Keys.
- Next to the key you want to delete, select Remove ().
- 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 likeuser_1.gitlab.com
anduser_2.gitlab.com
. Advanced configurations are more difficult to maintain, and these strings are easier to understand when you use tools likegit 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
Configure two-factor authentication (2FA)
You can set up two-factor authentication (2FA) for Git over SSH. We recommend using 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.
Troubleshooting
TLS: server sent certificate containing RSA key larger than 8192 bits
In GitLab 16.3 and later, Go limits RSA keys to a maximum of 8192 bits. To check the length of a key:
openssl rsa -in <your-key-file> -text -noout | grep "Key:"
Replace any key longer than 8192 bits with a shorter key.
Password prompt with git clone
When you run git clone
, you may be prompted for a password, like git@gitlab.example.com's password:
.
This indicates that 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 to manually register your private SSH key by using
ssh-agent
. - Try to debug the connection by running
ssh -Tv git@example.com
. Replaceexample.com
with your GitLab URL. - Ensure you followed all the instructions in Use SSH on Microsoft Windows.
Could not resolve hostname
error
You may receive the following error when verifying that you can connect:
ssh: Could not resolve hostname gitlab.example.com: nodename nor servname provided, or not known
If you receive this error, restart your terminal and try the command again.
Key enrollment failed: invalid format
error
You may receive the following error when generating an SSH key pair for a FIDO2 hardware security key:
Key enrollment failed: invalid format
You can troubleshoot this by trying the following:
- Run the
ssh-keygen
command usingsudo
. - Verify your FIDO2 hardware security key supports the key type provided.
- Verify the version of OpenSSH is 8.2 or greater by
running
ssh -V
.