adds private key identities to the
OpenSSH authentication agent
ssh-add adds private key identities to the
ssh-agent(1). When run without arguments, it adds the files
~/.ssh/id_dsa. After loading a private key,
ssh-add will try to load corresponding certificate
information from the filename obtained by appending
-cert.pub to the name of the private key file.
Alternative file names can be given on the command line.
If any file requires a passphrase,
asks for the passphrase from the user. The passphrase is read from the
ssh-add retries the last passphrase if
multiple identity files are given.
The authentication agent must be running and the
SSH_AUTH_SOCK environment variable must contain the
name of its socket for
ssh-add to work.
The options are as follows:
- Indicates that added identities should be subject to confirmation before being used for authentication. Confirmation is performed by ssh-askpass(1). Successful confirmation is signaled by a zero exit status from ssh-askpass(1), rather than text entered into the requester.
- Deletes all identities from the agent.
- Instead of adding identities, removes identities from the agent. If
ssh-addhas been run without arguments, the keys for the default identities and their corresponding certificates will be removed. Otherwise, the argument list will be interpreted as a list of paths to public key files to specify keys and certificates to be removed from the agent. If no public key is found at a given path,
ssh-addwill append .pub and retry. If the argument list consists of “-” then
ssh-addwill read public keys to be removed from standard input.
- Specifies the hash algorithm used when displaying key fingerprints. Valid options are: “md5” and “sha256”. The default is “sha256”.
- Remove keys provided by the PKCS#11 shared library pkcs11.
- Specifies a known hosts file to look up hostkeys when using
destination-constrained keys via the
-hflag. This option may be specified multiple times to allow multiple files to be searched. If no files are specified,
ssh-addwill use the default ssh_config(5) known hosts files: ~/.ssh/known_hosts, ~/.ssh/known_hosts2, /etc/ssh/ssh_known_hosts, and /etc/ssh/ssh_known_hosts2.
- When adding keys, constrain them to be usable only through specific hosts
or to specific destinations.
Destination constraints of the form ‘[user@]dest-hostname’ permit use of the key only from the origin host (the one running ssh-agent(1)) to the listed destination host, with optional user name.
Constraints of the form ‘src-hostname>[user@]dst-hostname’ allow a key available on a forwarded ssh-agent(1) to be used through a particular host (as specified by ‘src-hostname’) to authenticate to a further host, specified by ‘dst-hostname’.
Multiple destination constraints may be added when loading keys. When attempting authentication with a key that has destination constraints, the whole connection path, including ssh-agent(1) forwarding, is tested against those constraints and each hop must be permitted for the attempt to succeed. For example, if key is forwarded to a remote host, ‘host-b’, and is attempting authentication to another host, ‘host-c’, then the operation will be successful only if ‘host-b’ was permitted from the origin host and the subsequent ‘host-b>host-c’ hop is also permitted by destination constraints.
Hosts are identified by their host keys, and are looked up from known hosts files by
ssh-add. Wildcards patterns may be used for hostnames and certificate host keys are supported. By default, keys added by
ssh-addare not destination constrained.
Destination constraints were added in OpenSSH release 8.9. Support in both the remote SSH client and server is required when using destination-constrained keys over a forwarded ssh-agent(1) channel.
It is also important to note that destination constraints can only be enforced by ssh-agent(1) when a key is used, or when it is forwarded by a cooperating ssh(1). Specifically, it does not prevent an attacker with access to a remote
SSH_AUTH_SOCKfrom forwarding it again and using it on a different host (but only to a permitted destination).
- Load resident keys from a FIDO authenticator.
- When loading keys into or deleting keys from the agent, process plain private keys only and skip certificates.
- Lists public key parameters of all identities currently represented by the agent.
- Lists fingerprints of all identities currently represented by the agent.
- Be quiet after a successful operation.
- Specifies a path to a library that will be used when adding FIDO authenticator-hosted keys, overriding the default of using the internal USB HID support.
- Add keys provided by the PKCS#11 shared library pkcs11.
- Tests whether the private keys that correspond to the specified pubkey files are usable by performing sign and verify operations on each.
- Set a maximum lifetime when adding identities to an agent. The lifetime may be specified in seconds or in a time format specified in sshd_config(5).
- Verbose mode. Causes
ssh-addto print debugging messages about its progress. This is helpful in debugging problems. Multiple
-voptions increase the verbosity. The maximum is 3.
- Unlock the agent.
- Lock the agent with a password.
SSH_ASKPASS and SSH_ASKPASS_REQUIRE
ssh-addneeds a passphrase, it will read the passphrase from the current terminal if it was run from a terminal. If
ssh-adddoes not have a terminal associated with it but
SSH_ASKPASSare set, it will execute the program specified by
SSH_ASKPASS(by default “ssh-askpass”) and open an X11 window to read the passphrase. This is particularly useful when calling
ssh-addfrom a .xsession or related script.
SSH_ASKPASS_REQUIREallows further control over the use of an askpass program. If this variable is set to “never” then
ssh-addwill never attempt to use one. If it is set to “prefer”, then
ssh-addwill prefer to use the askpass program instead of the TTY when requesting passwords. Finally, if the variable is set to “force”, then the askpass program will be used for all passphrase input regardless of whether
- Identifies the path of a UNIX-domain socket used to communicate with the agent.
- Specifies a path to a library that will be used when loading any FIDO authenticator-hosted keys, overriding the default of using the built-in USB HID support.
- Contains the DSA, ECDSA, authenticator-hosted ECDSA, Ed25519, authenticator-hosted Ed25519 or RSA authentication identity of the user.
Identity files should not be readable by anyone but the user. Note
ssh-add ignores identity files if they are
accessible by others.
Exit status is 0 on success, 1 if the specified command fails, and
ssh-add is unable to contact the authentication
ssh(1), ssh-agent(1), ssh-askpass(1), ssh-keygen(1), sshd(8)
OpenSSH is a derivative of the original and free ssh 1.2.12 release by Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo de Raadt and Dug Song removed many bugs, re-added newer features and created OpenSSH. Markus Friedl contributed the support for SSH protocol versions 1.5 and 2.0.