| 1 | SSH-AGENT(1) System General Commands Manual SSH-AGENT(1) |
|---|
| 2 | |
|---|
| 3 | NAME |
|---|
| 4 | ssh-agent - authentication agent |
|---|
| 5 | |
|---|
| 6 | SYNOPSIS |
|---|
| 7 | ssh-agent [-a bind_address] [-c | -s] [-d] [command [args ...]] |
|---|
| 8 | ssh-agent [-c | -s] -k |
|---|
| 9 | |
|---|
| 10 | DESCRIPTION |
|---|
| 11 | ssh-agent is a program to hold private keys used for public key authentiM-- |
|---|
| 12 | cation (RSA, DSA). The idea is that ssh-agent is started in the beginM-- |
|---|
| 13 | ning of an X-session or a login session, and all other windows or proM-- |
|---|
| 14 | grams are started as clients to the ssh-agent program. Through use of |
|---|
| 15 | environment variables the agent can be located and automatically used for |
|---|
| 16 | authentication when logging in to other machines using ssh(1). |
|---|
| 17 | |
|---|
| 18 | The options are as follows: |
|---|
| 19 | |
|---|
| 20 | -a bind_address |
|---|
| 21 | Bind the agent to the unix-domain socket bind_address. The |
|---|
| 22 | default is /tmp/ssh-XXXXXXXX/agent.<ppid>. |
|---|
| 23 | |
|---|
| 24 | -c Generate C-shell commands on stdout. This is the default if |
|---|
| 25 | SHELL looks like it's a csh style of shell. |
|---|
| 26 | |
|---|
| 27 | -s Generate Bourne shell commands on stdout. This is the default if |
|---|
| 28 | SHELL does not look like it's a csh style of shell. |
|---|
| 29 | |
|---|
| 30 | -k Kill the current agent (given by the SSH_AGENT_PID environment |
|---|
| 31 | variable). |
|---|
| 32 | |
|---|
| 33 | -d Debug mode. When this option is specified ssh-agent will not |
|---|
| 34 | fork. |
|---|
| 35 | |
|---|
| 36 | If a commandline is given, this is executed as a subprocess of the agent. |
|---|
| 37 | When the command dies, so does the agent. |
|---|
| 38 | |
|---|
| 39 | The agent initially does not have any private keys. Keys are added using |
|---|
| 40 | ssh-add(1). When executed without arguments, ssh-add(1) adds the files |
|---|
| 41 | $HOME/.ssh/id_rsa, $HOME/.ssh/id_dsa and $HOME/.ssh/identity. If the |
|---|
| 42 | identity has a passphrase, ssh-add(1) asks for the passphrase (using a |
|---|
| 43 | small X11 application if running under X11, or from the terminal if runM-- |
|---|
| 44 | ning without X). It then sends the identity to the agent. Several idenM-- |
|---|
| 45 | tities can be stored in the agent; the agent can automatically use any of |
|---|
| 46 | these identities. ssh-add -l displays the identities currently held by |
|---|
| 47 | the agent. |
|---|
| 48 | |
|---|
| 49 | The idea is that the agent is run in the user's local PC, laptop, or terM-- |
|---|
| 50 | minal. Authentication data need not be stored on any other machine, and |
|---|
| 51 | authentication passphrases never go over the network. However, the conM-- |
|---|
| 52 | nection to the agent is forwarded over SSH remote logins, and the user |
|---|
| 53 | can thus use the privileges given by the identities anywhere in the netM-- |
|---|
| 54 | work in a secure way. |
|---|
| 55 | |
|---|
| 56 | There are two main ways to get an agent setup: Either the agent starts a |
|---|
| 57 | new subcommand into which some environment variables are exported, or the |
|---|
| 58 | agent prints the needed shell commands (either sh(1) or csh(1) syntax can |
|---|
| 59 | be generated) which can be evalled in the calling shell. Later ssh(1) |
|---|
| 60 | looks at these variables and uses them to establish a connection to the |
|---|
| 61 | agent. |
|---|
| 62 | |
|---|
| 63 | The agent will never send a private key over its request channel. |
|---|
| 64 | Instead, operations that require a private key will be performed by the |
|---|
| 65 | agent, and the result will be returned to the requester. This way, priM-- |
|---|
| 66 | vate keys are not exposed to clients using the agent. |
|---|
| 67 | |
|---|
| 68 | A unix-domain socket is created and the name of this socket is stored in |
|---|
| 69 | the SSH_AUTH_SOCK environment variable. The socket is made accessible |
|---|
| 70 | only to the current user. This method is easily abused by root or |
|---|
| 71 | another instance of the same user. |
|---|
| 72 | |
|---|
| 73 | The SSH_AGENT_PID environment variable holds the agent's process ID. |
|---|
| 74 | |
|---|
| 75 | The agent exits automatically when the command given on the command line |
|---|
| 76 | terminates. |
|---|
| 77 | |
|---|
| 78 | FILES |
|---|
| 79 | $HOME/.ssh/identity |
|---|
| 80 | Contains the protocol version 1 RSA authentication identity of |
|---|
| 81 | the user. |
|---|
| 82 | |
|---|
| 83 | $HOME/.ssh/id_dsa |
|---|
| 84 | Contains the protocol version 2 DSA authentication identity of |
|---|
| 85 | the user. |
|---|
| 86 | |
|---|
| 87 | $HOME/.ssh/id_rsa |
|---|
| 88 | Contains the protocol version 2 RSA authentication identity of |
|---|
| 89 | the user. |
|---|
| 90 | |
|---|
| 91 | /tmp/ssh-XXXXXXXX/agent.<ppid> |
|---|
| 92 | Unix-domain sockets used to contain the connection to the authenM-- |
|---|
| 93 | tication agent. These sockets should only be readable by the |
|---|
| 94 | owner. The sockets should get automatically removed when the |
|---|
| 95 | agent exits. |
|---|
| 96 | |
|---|
| 97 | AUTHORS |
|---|
| 98 | OpenSSH is a derivative of the original and free ssh 1.2.12 release by |
|---|
| 99 | Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo |
|---|
| 100 | de Raadt and Dug Song removed many bugs, re-added newer features and creM-- |
|---|
| 101 | ated OpenSSH. Markus Friedl contributed the support for SSH protocol |
|---|
| 102 | versions 1.5 and 2.0. |
|---|
| 103 | |
|---|
| 104 | SEE ALSO |
|---|
| 105 | ssh(1), ssh-add(1), ssh-keygen(1), sshd(8) |
|---|
| 106 | |
|---|
| 107 | BSD September 25, 1999 BSD |
|---|
