118 lines
5.3 KiB
Plaintext
118 lines
5.3 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 [-a bind_address] [-c | -s] [-t life] [-d] [command [args ...]]
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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 authenti-
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cation (RSA, DSA). The idea is that ssh-agent is started in the begin-
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ning of an X-session or a login session, and all other windows or pro-
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grams are started as clients to the ssh-agent program. Through use of
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environment variables the agent can be located and automatically used for
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authentication when logging in to other 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 de-
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fault is /tmp/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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-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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-k Kill the current agent (given by the SSH_AGENT_PID environment
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variable).
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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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-d Debug mode. When this option is specified ssh-agent will not
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fork.
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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 and ~/.ssh/identity. If the identity has a
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passphrase, ssh-add(1) asks for the passphrase (using a small X11 appli-
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cation if running under X11, or from the terminal if running without X).
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It then sends the identity to the agent. Several identities can be
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stored in the agent; the agent can automatically use any of these identi-
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ties. ssh-add -l displays the 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 ter-
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minal. Authentication data need not be stored on any other machine, and
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authentication passphrases never go over the network. However, the con-
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nection 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 net-
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work 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 evalled 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 con-
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nection to the agent.
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The agent will never send a private key over its request channel. In-
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stead, 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, pri-
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vate 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 anoth-
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er 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_rsa
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Contains the protocol version 2 RSA authentication identity of
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the user.
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/tmp/ssh-XXXXXXXXXX/agent.<ppid>
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Unix-domain sockets used to contain the connection to the authen-
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tication agent. These sockets should only be readable by the
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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 cre-
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ated OpenSSH. Markus Friedl contributed the support for SSH protocol
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versions 1.5 and 2.0.
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OpenBSD 4.2 June 5, 2007 2
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