1SSH-AGENT(1) BSD General Commands Manual SSH-AGENT(1)
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4 ssh-agent — OpenSSH authentication agent
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7 ssh-agent [-c | -s] [-Dd] [-a bind_address] [-E fingerprint_hash]
8 [-P allowed_providers] [-t life]
9 ssh-agent [-a bind_address] [-E fingerprint_hash] [-P allowed_providers]
10 [-t life] command [arg ...]
11 ssh-agent [-c | -s] -k
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14 ssh-agent is a program to hold private keys used for public key authenti‐
15 cation. Through use of environment variables the agent can be located
16 and automatically used for authentication when logging in to other
17 machines using ssh(1).
18 The options are as follows:
20 -a bind_address
22 Bind the agent to the UNIX-domain socket bind_address. The
23 default is $TMPDIR/ssh-XXXXXXXXXX/agent.<ppid>.
24 -c Generate C-shell commands on stdout. This is the default if
26 SHELL looks like it's a csh style of shell.
27 -D Foreground mode. When this option is specified ssh-agent will
29 not fork.
30 -d Debug mode. When this option is specified ssh-agent will not
32 fork and will write debug information to standard error.
33 -E fingerprint_hash
35 Specifies the hash algorithm used when displaying key finger‐
36 prints. Valid options are: “md5” and “sha256”. The default is
37 “sha256”.
38 -k Kill the current agent (given by the SSH_AGENT_PID environment
40 variable).
41 -P allowed_providers
43 Specify a pattern-list of acceptable paths for PKCS#11 provider
44 and FIDO authenticator middleware shared libraries that may be
45 used with the -S or -s options to ssh-add(1). Libraries that do
46 not match the pattern list will be refused. See PATTERNS in
47 ssh_config(5) for a description of pattern-list syntax. The
48 default list is “/usr/lib/*,/usr/local/lib/*”.
49 -s Generate Bourne shell commands on stdout. This is the default if
51 SHELL does not look like it's a csh style of shell.
52 -t life
54 Set a default value for the maximum lifetime of identities added
55 to the agent. The lifetime may be specified in seconds or in a
56 time format specified in sshd_config(5). A lifetime specified
57 for an identity with ssh-add(1) overrides this value. Without
58 this option the default maximum lifetime is forever.
59 command [arg ...]
61 If a command (and optional arguments) is given, this is executed
62 as a subprocess of the agent. The agent exits automatically when
63 the command given on the command line terminates.
64 There are two main ways to get an agent set up. The first is at the
66 start of an X session, where all other windows or programs are started as
67 children of the ssh-agent program. The agent starts a command under
68 which its environment variables are exported, for example ssh-agent xterm
69 &. When the command terminates, so does the agent.
70 The second method is used for a login session. When ssh-agent is
72 started, it prints the shell commands required to set its environment
73 variables, which in turn can be evaluated in the calling shell, for exam‐
74 ple eval `ssh-agent -s`.
75 In both cases, ssh(1) looks at these environment variables and uses them
77 to establish a connection to the agent.
78 The agent initially does not have any private keys. Keys are added using
80 ssh-add(1) or by ssh(1) when AddKeysToAgent is set in ssh_config(5).
81 Multiple identities may be stored in ssh-agent concurrently and ssh(1)
82 will automatically use them if present. ssh-add(1) is also used to
83 remove keys from ssh-agent and to query the keys that are held in one.
84 Connections to ssh-agent may be forwarded from further remote hosts using
86 the -A option to ssh(1) (but see the caveats documented therein), avoid‐
87 ing the need for authentication data to be stored on other machines.
88 Authentication passphrases and private keys never go over the network:
89 the connection to the agent is forwarded over SSH remote connections and
90 the result is returned to the requester, allowing the user access to
91 their identities anywhere in the network in a secure fashion.
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94 SSH_AGENT_PID When ssh-agent starts, it stores the name of the agent's
95 process ID (PID) in this variable.
96 SSH_AUTH_SOCK When ssh-agent starts, it creates a UNIX-domain socket and
98 stores its pathname in this variable. It is accessible
99 only to the current user, but is easily abused by root or
100 another instance of the same user.
101
103 $TMPDIR/ssh-XXXXXXXXXX/agent.<ppid>
104 UNIX-domain sockets used to contain the connection to the authen‐
105 tication agent. These sockets should only be readable by the
106 owner. The sockets should get automatically removed when the
107 agent exits.
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110 ssh(1), ssh-add(1), ssh-keygen(1), ssh_config(5), sshd(8)
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113 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
114 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
115 de Raadt and Dug Song removed many bugs, re-added newer features and cre‐
116 ated OpenSSH. Markus Friedl contributed the support for SSH protocol
117 versions 1.5 and 2.0.
118BSD June 22, 2020 BSD