Tribblix: manual page: ssh-add.1

SSH-ADD(1) User Commands SSH-ADD(1)

NAME

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

SYNOPSIS

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

DESCRIPTION

ssh-add adds private key identities to the authentication agent,
ssh-agent(1). When run without arguments, it adds the files
~/.ssh/id_rsa, ~/.ssh/id_ecdsa, ~/.ssh/id_ecdsa_sk, ~/.ssh/id_ed25519
and ~/.ssh/id_ed25519_sk. 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 When loading keys into or deleting keys from the agent, process
certificates only and skip plain keys.

-c 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.

-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_config(5) 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-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-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-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_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.
Certificate files may optionally be listed as command-line
arguments. If these are present, then they will be loaded into
the agent using any corresponding private keys loaded from the
PKCS#11 token.

-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_config(5).

-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-domain 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_ecdsa
~/.ssh/id_ecdsa_sk
~/.ssh/id_ed25519
~/.ssh/id_ed25519_sk
~/.ssh/id_rsa
Contains the 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.

illumos June 17, 2024 illumos