Manual: ssh-add
SSH-ADD(1) General Commands Manual SSH-ADD(1)
NAME
ssh-add — adds private key identities to the OpenSSH authentication agent
SYNOPSIS
ssh-add [-CcDdKkLlNqvXx] [-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. Con‐
firmation 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 ar‐
gument 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 speci‐
fied, 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 pat‐
terns 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 certifi‐
cates.
-L Lists public key parameters of all identities currently represented by the agent.
-l Lists fingerprints of all identities currently represented by the agent.
-N When adding certificates, by default ssh-add will request that the agent automatically delete the certificate
shortly after the certificate's expiry date. This flag suppresses this behaviour and does not specify a
lifetime for certificates added to an 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 com‐
mand-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 authentica‐
tion agent.
SEE ALSO
ssh(1), ssh-agent(1), ssh-askpass(1), ssh-keygen(1), sshd(8)
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.
Debian September 11, 2025 SSH-ADD(1)