129 lines
5.6 KiB
Plaintext
129 lines
5.6 KiB
Plaintext
SSH-AGENT(1) OpenBSD Reference Manual SSH-AGENT(1)
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NAME
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ssh-agent - authentication agent
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SYNOPSIS
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ssh-agent [-c | -s] [-d] [-a bind_address] [-t life] [command [arg ...]]
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ssh-agent [-c | -s] -k
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DESCRIPTION
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ssh-agent is a program to hold private keys used for public key
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authentication (RSA, DSA, ECDSA, ED25519). The idea is that ssh-agent is
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started in the beginning of an X-session or a login session, and all
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other windows or programs are started as clients to the ssh-agent
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program. Through use of environment variables the agent can be located
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and automatically used for authentication when logging in to other
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machines using ssh(1).
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The options are as follows:
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-a bind_address
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Bind the agent to the UNIX-domain socket bind_address. The
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default is $TMPDIR/ssh-XXXXXXXXXX/agent.<ppid>.
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-c Generate C-shell commands on stdout. This is the default if
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SHELL looks like it's a csh style of shell.
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-d Debug mode. When this option is specified ssh-agent will not
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fork.
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-k Kill the current agent (given by the SSH_AGENT_PID environment
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variable).
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-s Generate Bourne shell commands on stdout. This is the default if
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SHELL does not look like it's a csh style of shell.
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-t life
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Set a default value for the maximum lifetime of identities added
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to the agent. The lifetime may be specified in seconds or in a
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time format specified in sshd_config(5). A lifetime specified
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for an identity with ssh-add(1) overrides this value. Without
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this option the default maximum lifetime is forever.
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If a commandline is given, this is executed as a subprocess of the agent.
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When the command dies, so does the agent.
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The agent initially does not have any private keys. Keys are added using
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ssh-add(1). When executed without arguments, ssh-add(1) adds the files
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~/.ssh/id_rsa, ~/.ssh/id_dsa, ~/.ssh/id_ecdsa, ~/.ssh/id_ed25519 and
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~/.ssh/identity. If the identity has a passphrase, ssh-add(1) asks for
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the passphrase on the terminal if it has one or from a small X11 program
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if running under X11. If neither of these is the case then the
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authentication will fail. It then sends the identity to the agent.
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Several identities can be stored in the agent; the agent can
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automatically use any of these identities. ssh-add -l displays the
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identities currently held by the agent.
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The idea is that the agent is run in the user's local PC, laptop, or
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terminal. Authentication data need not be stored on any other machine,
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and authentication passphrases never go over the network. However, the
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connection to the agent is forwarded over SSH remote logins, and the user
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can thus use the privileges given by the identities anywhere in the
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network in a secure way.
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There are two main ways to get an agent set up: The first is that the
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agent starts a new subcommand into which some environment variables are
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exported, eg ssh-agent xterm &. The second is that the agent prints the
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needed shell commands (either sh(1) or csh(1) syntax can be generated)
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which can be evaluated in the calling shell, eg eval `ssh-agent -s` for
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Bourne-type shells such as sh(1) or ksh(1) and eval `ssh-agent -c` for
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csh(1) and derivatives.
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Later ssh(1) looks at these variables and uses them to establish a
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connection to the agent.
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The agent will never send a private key over its request channel.
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Instead, operations that require a private key will be performed by the
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agent, and the result will be returned to the requester. This way,
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private keys are not exposed to clients using the agent.
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A UNIX-domain socket is created and the name of this socket is stored in
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the SSH_AUTH_SOCK environment variable. The socket is made accessible
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only to the current user. This method is easily abused by root or
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another instance of the same user.
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The SSH_AGENT_PID environment variable holds the agent's process ID.
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The agent exits automatically when the command given on the command line
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terminates.
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FILES
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~/.ssh/identity
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Contains the protocol version 1 RSA authentication identity of
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the user.
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~/.ssh/id_dsa
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Contains the protocol version 2 DSA authentication identity of
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the user.
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~/.ssh/id_ecdsa
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Contains the protocol version 2 ECDSA authentication identity of
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the user.
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~/.ssh/id_ed25519
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Contains the protocol version 2 ED25519 authentication identity
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of the user.
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~/.ssh/id_rsa
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Contains the protocol version 2 RSA authentication identity of
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the user.
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$TMPDIR/ssh-XXXXXXXXXX/agent.<ppid>
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UNIX-domain sockets used to contain the connection to the
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authentication agent. These sockets should only be readable by
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the owner. The sockets should get automatically removed when the
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agent exits.
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SEE ALSO
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ssh(1), ssh-add(1), ssh-keygen(1), sshd(8)
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AUTHORS
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OpenSSH is a derivative of the original and free ssh 1.2.12 release by
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Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
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de Raadt and Dug Song removed many bugs, re-added newer features and
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created OpenSSH. Markus Friedl contributed the support for SSH protocol
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versions 1.5 and 2.0.
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OpenBSD 5.5 December 7, 2013 OpenBSD 5.5
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