ssh-add (1) - Linux Manuals

ssh-add: adds private key identities to the OpenSSH authentication agent

NAME

ssh-add - adds private key identities to the OpenSSH authentication agent

SYNOPSIS

ssh-add [-cDdKkLlqvXx [-E fingerprint_hash ] ] [-H hostkey_file ] [-h destination_constraint ] [-S provider ] [-t life ] [file ... ]
ssh-add -s pkcs11
ssh-add -e pkcs11
ssh-add -T pubkey ...

DESCRIPTION

ssh-add adds private key identities to the authentication agent, ssh-agent1. When run without arguments, it adds the files ~/.ssh/id_rsa ~/.ssh/id_ecdsa ~/.ssh/id_ecdsa_sk ~/.ssh/id_ed25519 ~/.ssh/id_ed25519_sk and ~/.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, ssh-add asks for the passphrase from the user. The passphrase is read from the user's tty. 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:

-c

Indicates that added identities should be subject to confirmation before being used for authentication. Confirmation is performed by ssh-askpass1. Successful confirmation is signaled by a zero exit status from ssh-askpass1, rather than text entered into the requester.

-D

Deletes all identities from the agent.

-d

Instead of adding identities, removes identities from the agent. If ssh-add has 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-add will append .pub and retry. If the argument list consists of ``-'' then ssh-add will read public keys to be removed from standard input.

-E fingerprint_hash

Specifies the hash algorithm used when displaying key fingerprints. Valid options are: ``md5'' and ``sha256'' The default is ``sha256''

-e pkcs11

Remove keys provided by the PKCS#11 shared library pkcs11

-H hostkey_file

Specifies a known hosts file to look up hostkeys when using destination-constrained keys via the -h flag. This option may be specified multiple times to allow multiple files to be searched. If no files are specified, ssh-add will use the default ssh_config5 known hosts files: ~/.ssh/known_hosts ~/.ssh/known_hosts2 /etc/ssh/ssh_known_hosts and /etc/ssh/ssh_known_hosts2

-h destination_constraint

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-agent1) 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-agent1 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-agent1 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-add are 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-agent1 channel.

It is also important to note that destination constraints can only be enforced by ssh-agent1 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_SOCK from forwarding it again and using it on a different host (but only to a permitted destination).

-K

Load resident keys from a FIDO authenticator.

-k

When loading keys into or deleting keys from the agent, process plain private keys only and skip certificates.

-L

Lists public key parameters of all identities currently represented by the agent.

-l

Lists fingerprints of all identities currently represented by the agent.

-q

Be quiet after a successful operation.

-S provider

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.

-s pkcs11

Add keys provided by the PKCS#11 shared library pkcs11

-T pubkey ...

Tests whether the private keys that correspond to the specified pubkey files are usable by performing sign and verify operations on each.

-t life

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_config5.

-v

Verbose mode. Causes ssh-add to print debugging messages about its progress. This is helpful in debugging problems. Multiple -v options increase the verbosity. The maximum is 3.

-X

Unlock the agent.

-x

Lock the agent with a password.

ENVIRONMENT

DISPLAY, SSH_ASKPASS and SSH_ASKPASS_REQUIRE

If ssh-add needs a passphrase, it will read the passphrase from the current terminal if it was run from a terminal. If ssh-add does not have a terminal associated with it but DISPLAY and SSH_ASKPASS are 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-add from a .xsession or related script.

SSH_ASKPASS_REQUIRE allows further control over the use of an askpass program. If this variable is set to ``never'' then ssh-add will never attempt to use one. If it is set to ``prefer'' then ssh-add will 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 DISPLAY is set.

SSH_AUTH_SOCK

Identifies the path of a UNIX socket used to communicate with the agent.

SSH_SK_PROVIDER

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.

FILES

~/.ssh/id_dsa

~/.ssh/id_ecdsa

~/.ssh/id_ecdsa_sk

~/.ssh/id_ed25519

~/.ssh/id_ed25519_sk

~/.ssh/id_rsa

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 that ssh-add ignores identity files if they are accessible by others.

EXIT STATUS

Exit status is 0 on success, 1 if the specified command fails, and 2 if ssh-add is unable to contact the authentication agent.

AUTHORS

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.