Windows PowerShell command on Get-command sshd

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System Administration Commands sshd(1M)

NAME

sshd - secure shell daemon

SYNOPSIS

sshd [-deiqtD46] [-b bits] [-f config_file]

[-g login_grace_time] [-h host_key_file]

[-k key_gen_time] [-p port] [-V client_protocol_id]

DESCRIPTION

The sshd (Secure Shell daemon) is the daemon program for

ssh(1). Together these programs replace rlogin and rsh, and provide secure encrypted communications between two untrusted hosts over an insecure network. The programs are intended to be as easy to install and use as possible.

sshd is the daemon that listens for connections from

clients. It forks a new daemon for each incoming connection.

The forked daemons handle key exchange, encryption, authen-

tication, command execution, and data exchange.

This implementation of sshd supports both SSH protocol ver-

sions 1 and 2 simultaneously. Because of security weaknesses in the v1 protocol, sites should run only v2, if possible. In the default configuration, only protocol v2 is enabled for the server. To enable v1 and v2 simultaneously, see the

instructions in sshd_config(4).

Support for v1 is provided to help sites with existing ssh v1 clients and servers to transition to v2. v1 might not be supported in a future release. SSH Protocol Version 1

Each host has a host-specific RSA key (normally 1024 bits)

used to identify the host. Additionally, when the daemon starts, it generates a server RSA key (normally 768 bits). This key is normally regenerated every hour if it has been used, and is never stored on disk.

Whenever a client connects the daemon responds with its pub-

lic host and server keys. The client compares the RSA host key against its own database to verify that it has not

changed. The client then generates a 256-bit random number.

It encrypts this random number using both the host key and the server key, and sends the encrypted number to the server. Both sides then use this random number as a session key which is used to encrypt all further communications in the session. The rest of the session is encrypted using a

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conventional cipher, currently Blowfish or 3DES, with 3DES being used by default. The client selects the encryption algorithm to use from those offered by the server.

Next, the server and the client enter an authentication dia-

log. The client tries to authenticate itself using .rhosts authentication, .rhosts authentication combined with RSA

host authentication, RSA challenge-response authentication,

or password-based authentication.

Rhosts authentication is normally disabled because it is fundamentally insecure, but can be enabled in the server configuration file if desired. System security is not improved unless rshd(1M), rlogind(1M), rexecd(1M), and rexd(1M) are disabled (thus completely disabling rlogin(1) and rsh(1) into the machine). SSH Protocol Version 2 Version 2 works similarly to version 1: Each host has a

host-specific DSA/RSA key. However, when the daemon starts,

it does not generate a server key. Forward security is pro-

vided through a Diffie-Hellman key agreement. This key

agreement results in a shared session key. The rest of the session is encrypted using a symmetric cipher, currently

128-bit AES, Blowfish, 3DES, or AES. The client selects the

encryption algorithm to use from those offered by the server. Additionally, session integrity is provided through

a cryptographic message authentication code (hmac-sha1 or

hmac-md5).

Protocol version 2 provides a public key based user authen-

tication method (PubKeyAuthentication) GSS-API based user

authentication, conventional password authentication, and a

generic prompt/reply protocol for password-based authentica-

tion. Command Execution and Data Forwarding If the client successfully authenticates itself, a dialog for preparing the session is entered. At this time the

client can request things like allocating a pseudo-tty, for-

warding X11 connections, forwarding TCP/IP connections, or forwarding the authentication agent connection over the secure channel. Finally, the client either requests a shell or execution of a command. The sides then enter session mode. In this mode,

either side may send data at any time, and such data is for-

warded to/from the shell or command on the server side, and

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the user terminal on the client side. When the user program terminates and all forwarded X11 and other connections have been closed, the server sends command exit status to the client, and both sides exit.

sshd can be configured using command-line options or the

configuration file /etc/ssh/ssh_config, described in

ssh_config(4). Command-line options override values speci-

fied in the configuration file.

sshd rereads its configuration file when it receives a

hangup signal, SIGHUP, by executing itself with the name it

was started as, that is, /usr/lib/ssh/sshd.

Host Access Control

The sshd daemon uses TCP Wrappers to restrict access to

hosts. It uses the service name of sshd for hosts_access().

For more information on TCP Wrappers see tcpd(1M) and

hosts_access(3) man pages, which are part of the SUNWsfman

package (they are not SunOS man pages). TCP wrappers binaries, including libwrap, are in SUNWtcpd, a required

package for SUNWsshdu, the package containing sshd.

OPTIONS

The options for sshd are as follows:

-b bits

Specifies the number of bits in the server key (the default is 768).

-d

Debug mode. The server sends verbose debug output to the system log, and does not put itself in the background. The server also will not fork and will only process one connection. This option is only intended for debugging

for the server. Multiple -d options increase the debug-

ging level. Maximum is 3.

-e

When this option is specified, sshd will send the output

to standard error instead of to the system log.

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-f configuration_file

Specifies the name of the configuration file. The

default is /etc/ssh/sshd_config. sshd refuses to start

if there is no configuration file.

-g login_grace_time

Gives the grace time for clients to authenticate them-

selves (the default is 300 seconds). If the client fails to authenticate the user within this number of seconds,

the server disconnects and exits. A value of zero indi-

cates no limit.

-h host_key_file

Specifies a file from which a host key is read. This

option must be given if sshd is not run as root (as the

normal host key files are normally not readable by any-

one but root). The default is /etc/ssh/ssh_host_key for

protocol version 1, and /etc/ssh/ssh_host_rsa_key and

/etc/ssh/ssh_host_dsa_key for protocol version 2. It is

possible to have multiple host key files for the dif-

ferent protocol versions and host key algorithms.

-i

Specifies that sshd is being run from inetd. sshd is

normally not run from inetd because it needs to generate the server key before it can respond to the client, and this may take tens of seconds. Clients would have to wait too long if the key was regenerated every time. However, with small key sizes (for example, 512) using

sshd from inetd may be reasonable.

-k key_gen_time

(SSHv1-specific) Specifies how often the server key is

regenerated (the default is 3600 seconds, or one hour). The motivation for regenerating the key fairly often is that the key is not stored anywhere, and after about an hour, it becomes impossible to recover the key for decrypting intercepted communications even if the machine is cracked into or physically seized. A value of zero indicates that the key will never be regenerated.

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-o option

Can be used to specify options in the format used in the configuration file. This is useful for specifying

options for which there are no separate command-line

flags.

-p port

Specifies the port on which the server listens for con-

nections (the default is 22).

-q

Quiet mode. Nothing is sent to the system log. Normally the beginning, authentication, and termination of each connection is logged.

-t

Test mode. Check only the validity of the configuration file and the sanity of the keys. This is useful for

updating sshd reliably as configuration options might

change.

-D

When this option is specified sshd does not detach and

does not become a daemon. This allows easy monitoring of

sshd.

-4

Forces sshd to use IPv4 addresses only.

-6

Forces sshd to use IPv6 addresses only.

EXTENDED DESCRIPTION

authorized_keys File Format

The $HOME/.ssh/authorized_keys file lists the public keys

that are permitted for RSA authentication in protocol ver-

sion 1 and for public key authentication (PubkeyAuthentica-

tion) in protocol version 2. The AuthorizedKeysFile

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configuration option can be used to specify an alternative file. Each line of the file contains one key (empty lines and

lines starting with a hash mark [#] are ignored as com-

ments). For each RSA key for protocol version 1, the file consists

of the following space-separated fields:

options bits exponent modulus comment For the public key for protocol version 2, the file consists

of the following space-separated fields:

options key-type base64-encoding-key comment

For protocol version 2, key-type is one of ssh-rsa or ssh-

dsa. The options field is optional; its presence is determined by whether the line starts with a number. (The option field never starts with a number.) The bits, exponent, and modulus fields give the RSA key; the comment field is a convenient place for you to identify the key. Lines in this file are usually several hundred bytes long (because of the size of the key modulus). You will find it very inconvenient to type them in; instead, copy the public key file and edit it. Permissions of this file must be set so that it is not world or group writable. See the StrictModes option of

sshd_config(4).

The options (if present) consist of comma-separated option

specifications. No spaces are permitted, except within dou-

ble quotes. The following option specifications are sup-

ported:

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from="pattern-list"

Specifies that, in addition to public key authentica-

tion, the canonical name of the remote host must be

present in the comma-separated list of patterns (`*' and

`?' serve as wildcards). The list can also contain negated patterns by prefixing the patterns with `!'. If the canonical host name matches a negated pattern, the key is not accepted. The purpose of this option is to give you the option of increasing security: public key authentication by itself does not trust the network or name servers or anything but the key. However, if someone manages to steal the key, possession of the key would permit the intruder to log in from anywhere in the world. This option makes using a stolen key more difficult, because name servers and routers would have to be compromised, in addition to just the key. command="command" Specifies that the command is executed whenever this key is used for authentication. The command supplied by the user (if any) is ignored. The command is run on a pty if the client requests a pty; otherwise it is run without a

tty. If an 8-bit clean channel is required, one must not

request a pty or should specify no-pty. You can include

a quote in the command by escaping it with a backslash. This option might be useful to restrict certain public keys from performing a specific operation. An example is a key that permits remote backups but nothing else. Note

that the client can specify TCP/IP and/or X11 forwarding unless they are explicitly prohibited from doing so. Also note that this option applies to shell, command, or subsystem execution.

environment="NAME=value"

Specifies that the string NAME=value is to be added to

the environment when logging in using this key. Environ-

ment variables set this way override other default environment values. Multiple options of this type are permitted. Environment processing is disabled by default and is controlled via the PermitUserEnvironment option.

no-port-forwarding

Forbids TCP/IP forwarding when this key is used for

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authentication. Any port forward requests by the client will return an error. This might be used, for example, in connection with the command option.

no-X11-forwarding

Forbids X11 forwarding when this key is used for authen-

tication. Any X11 forward requests by the client will return an error.

no-agent-forwarding

Forbids authentication agent forwarding when this key is used for authentication.

no-pty

Prevents tty allocation (a request to allocate a pty will fail). permitopen="host:port"

Limit local ssh -L port forwarding such that it can con-

nect only to the specified host and port. IPv6 addresses can be specified with an alternative syntax: host/port. You can invoke multiple permitopen options, with each instance separated by a comma. No pattern matching is performed on the specified hostnames. They must be literal domains or addresses.

ssh_known_hosts File Format

The /etc/ssh/ssh_known_hosts and $HOME/.ssh/known_hosts

files contain host public keys for all known hosts. The glo-

bal file should be prepared by the administrator (optional),

and the per-user file is maintained automatically: whenever

the user connects from an unknown host its key is added to

the per-user file.

For the RSA key for protocol version 1, these files consist

of the following space-separated fields:

hostnames bits exponent modulus comment

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For the public key for protocol version 2, these files con-

sist of the following space-separated fields:

hostnames key-type base64-encoding-key comment

For protocol version 2, key-type is one of ssh-rsa or ssh-

dsa.

Hostnames is a comma-separated list of patterns (* and ? act

as wildcards); each pattern in turn is matched against the canonical host name (when authenticating a client) or

against the user-supplied name (when authenticating a

server). A pattern can also be preceded by ! to indicate negation: if the host name matches a negated pattern, it is

not accepted (by that line) even if it matched another pat-

tern on the line. Alternately, hostnames can be stored in a hashed form, which hides host names and addresses should the file's contents be disclosed. Hashed hostnames start with a vertical bar (|) character. Only one hashed hostname can appear on a single line and none of the above negation or wildcard operators may be applied. Bits, exponent, and modulus are taken directly from the RSA host key; they can be obtained, for example, from

/etc/ssh/ssh_host_rsa_key.pub. The optional comment field

continues to the end of the line, and is not used.

Lines starting with a hash mark (#) and empty lines are

ignored as comments. When performing host authentication, authentication is accepted if any matching line has the proper key. It is thus permissible (but not recommended) to have several lines or different host keys for the same names. This will inevitably happen when short forms of host names from different domains are put in the file. It is possible that the files contain conflicting information; authentication is accepted if valid information can be found from either file.

The lines in these files are typically hundreds of charac-

ters long. You should definitely not type in the host keys

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by hand. Rather, generate them by a script or by taking

/etc/ssh/ssh_host_rsa_key.pub and adding the host names at

the front. ENVIRONMENT VARIABLES

sshd sets the following environment variables for commands

executed by ssh users: DISPLAY

Indicates the location of the X11 server. It is automat-

ically set by sshd to point to a value of the form

hostname:n, where hostname indicates the host where the shell runs, and n is an integer greater than or equal to

1. ssh uses this special value to forward X11 connec-

tions over the secure channel. Unless you have important reasons to do otherwise, you should not set DISPLAY explicitly, as that will render the X11 connection insecure and will require you to manually copy any required authorization cookies. HOME Set to the path of the user's home directory.

LANG, LC_ALL, LC_COLLATE, LC_CTYPE, LC_MESSAGES,

LC_MONETARY, LC_NUMERIC, LC_TIME

A locale setting. The locale defaults to that of sshd

(usually the system-wide default locale), or is nego-

tiated between the client and server during initial key exchange (as per RFC 4253). Following initial key exchange, each of the variables can be overriden in the following sequence: 1. If a locale setting is set in a client's

environment and that client supports "Environ-

ment Variable Passing" (see RFC 4254), then the setting will be passed over to the server side. 2. If the public key authentication method was

used to authenticate the server and the Permi-

tUserEnvironment variable in sshd_config(4) is

set to yes on the server side, then the setting

can be changed through the use of the environ-

ment option in the client's AuthorizedKeysFile file. 3. The setting can be change in the client's

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~/.ssh/environment file on the server.

See PermitUserEnvironment in sshd_config(4) as to when

the AuthorizedKeysFile and ~/.ssh/environment files are processed and used for setting the user environment.

LOGNAME

Synonym for USER. Set for compatibility with systems that use this variable. MAIL Set to point to the user's mailbox.

SSH_AUTH_SOCK

Indicates the path of a unix-domain socket used to com-

municate with the agent.

SSH_CONNECTION

Identifies the client and server ends of the connection.

The variable contains four space-separated values:

client IP address, client port number, server IP address and server port number.

SSH_CLIENT

Identifies the client end of the connection. The vari-

able contains three space-separated values: client IP

address, client port number, and server port number.

SSH_TTY

Set to the name of the tty (path to the device) associ-

ated with the current shell or command. If the current session has no tty, this variable is not set. TZ Indicates the present timezone, if TIMEZONE is set in /etc/default/login or if TZ was set when the daemon was started.

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HZ If set in /etc/default/login, the daemon sets it to the same value. SHELL The user's shell, if ALTSHELL=YES in /etc/default/login. PATH Set to the value of PATH or SUPATH (see login(1)) in /etc/default/login, or, if not set, to /usr/bin:/bin. USER Set to the name of the user logging in.

Additionally, sshd reads $HOME/.ssh/environment and adds

lines of the format VARNAME=value to the environment.

EXAMPLES

In the following examples, certain lines might wrap due to line length limits in your display. You should nevertheless consider the wrapped line as a single line.

Example 1 authorized_key File Entries

The following are examples of authorized_key file entries

for protocol 1: 1024 33 12121...312314325 ylo@foo.bar from="*.niksula.hut.fi,!pc.niksula.hut.fi" 1024 35 23...2334 ylo@niksula

command="dump /home",no-pty,no-port-forwarding 1024 33 23...2323 backup.hut.fi

Example 2 authorized_key File Entries for Protocol 2

The following are examples of authorized_key file entries

for protocol 2:

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ssh-rsa AAAAB3NzaC1y.....EU88ovYKg4GfclWGCFYTuw8= ylo@foo.bar

from="*.niksula.hut.fi" ssh-rsa AAAAB3NzaC...uw8= ylo@niksula

command="dump /home",no-pty,no-port-forwarding ssh-rsa AA..8= backup.hut.fi

Example 3 ssh_known_hosts File Entries for Protocol 1

The following are examples of ssh_known_hosts file entries

for protocol 1: closenet,closenet.hut.fi,...,130.233.208.41 1024 37 159...93 closenet.hut.fi

Example 4 ssh_known_hosts File Entries for Protocol 2

The following are examples of ssh_known_hosts file entries

for protocol 2:

closenet,closenet.hut.fi,...,130.233.208.41 ssh-rsa AA..8= closenet.hut.fi

EXIT STATUS The following exit values are returned: 0 Successful completion. >0 An error occurred. FILES /etc/default/login

Contains defaults for several sshd_config parameters,

environment variables, and other environmental factors. The following parameters affect environment variables (see login(1) and descriptions of these variables, above): o TIMEZONE o HZ o ALTSHELL

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o PATH o SUPATH The following /etc/default/login parameters supply

default values for corresponding sshd_config(4) parame-

ters:

o CONSOLE (see PermitRootLogin in sshd_config(4))

o PASSREQ (see PermitEmptyPasswords in

sshd_config(4))

o TIMEOUT (see LoginGraceTime in sshd_config(4))

The following /etc/default/login parameters: o UMASK o ULIMIT

...set the umask(2) and file size limit of, respec-

tively, the shells and commands spawned by sshd.

Finally, two /etc/default/login parameters affect the

maximum allowed login attempts per-connection using

interactive user authentication methods (for example,

keyboard-interactive but not publickey), as per

o SYSLOG_FAILED_LOGINS

/etc/ssh/sshd_config

Contains configuration data for sshd. This file should

be writable by root only, but it is recommended (though

not necessary) that it be world-readable.

/etc/ssh/ssh_host_key

/etc/ssh/ssh_host_dsa_key

/etc/ssh/ssh_host_rsa_key

Contains the private part of the host key. This file should only be owned by root, readable only by root, and

not accessible to others. sshd does not start if this

file is group/world-accessible.

/etc/ssh/ssh_host_key.pub

/etc/ssh/ssh_host_dsa_key.pub

/etc/ssh/ssh_host_rsa_key.pub

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Contains the public part of the host key. This file

should be world-readable but writable only by root. Its

contents should match the private part. This file is not

used for encryption; it is provided only for the con-

venience of the user so its contents can be copied to known hosts files. These two files are created using

ssh-keygen(1).

/var/run/sshd.pid

Contains the process ID of the sshd listening for con-

nections. If there are several daemons running con-

currently for different ports, this contains the pid of the one started last. The content of this file is not

sensitive; it can be world-readable. You can use the

PidFile keyword in sshd_config to specify a file other

than /var/run/sshd.pid. See sshd_config(4).

/etc/ssh/ssh_known_hosts and $HOME/.ssh/known_hosts

These files are consulted when using rhosts with public key host authentication to check the public key of the host. The key must be listed in one of these files to be accepted. The client uses the same files to verify that the remote host is the one it intended to connect. These files should be writable only by root or the owner.

/etc/ssh/ssh_known_hosts should be world-readable, and

$HOME/.ssh/known_hosts can but need not be world-

readable. /etc/nologin

If this file exists, sshd refuses to let anyone except

root log in. The contents of the file are displayed to

anyone trying to log in, and non-root connections are

refused. The file should be world-readable.

$HOME/.ssh/authorized_keys

Lists the public keys (RSA or DSA) that can be used to log into the user's account. This file must be readable by root. This might, on some machines, imply that it is

world-readable if the user's home directory resides on

an NFS volume. It is recommended that it not be accessi-

ble by others. The format of this file is described above. Users will place the contents of their

identity.pub, id_dsa.pub and/or id_rsa.pub files into

this file, as described in ssh-keygen(1).

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$HOME/.rhosts

This file contains host-username pairs, separated by a

space, one per line. The given user on the corresponding host is permitted to log in without password. The same

file is used by rlogind and rshd. The file must be writ-

able only by the user; it is recommended that it not be

accessible by others. It is also possible to use net-

groups in the file. Either host or user name may be of the form +@groupname to specify all hosts or all users in the group.

$HOME/.shosts

For ssh, this file is exactly the same as for .rhosts. However, this file is not used by rlogin and rshd, so using this permits access using SSH only. /etc/hosts.equiv This file is used during .rhosts authentication. In its simplest form, this file contains host names, one per line. Users on these hosts are permitted to log in without a password, provided they have the same user

name on both machines. The host name can also be fol-

lowed by a user name; such users are permitted to log in as any user on this machine (except root). Additionally, the syntax +@group can be used to specify netgroups.

Negated entries start with a hyphen (-).

If the client host/user is successfully matched in this file, login is automatically permitted, provided the client and server user names are the same. Additionally, successful RSA host authentication is normally required.

This file must be writable only by root; it is recom-

mended that it be world-readable.

Warning: It is almost never a good idea to use user names in hosts.equiv. Beware that it really means that the named user(s) can log in as anybody, which includes bin, daemon, adm, and other accounts that own critical binaries and directories. For practical purposes, using a user name grants the user root access. Probably the only valid use for user names is in negative entries. This warning also applies to rsh/rlogin. /etc/ssh/moduli A private file.

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/etc/ssh/shosts.equiv

This file is processed exactly as /etc/hosts.equiv. How-

ever, this file might be useful in environments that want to run both rsh/rlogin and ssh.

$HOME/.ssh/environment

This file is read into the environment at login (if it exists). It can contain only empty lines, comment lines

(that start with #), and assignment lines of the form

name=value. The file should be writable only by the

user; it need not be readable by anyone else. Environ-

ment processing is disabled by default and is controlled by means of the PermitUserEnvironment option.

$HOME/.ssh/rc

If this file exists, it is run with /bin/sh after read-

ing the environment files but before starting the user's shell or command. If X11 spoofing is in use, this will receive the proto cookie pair in standard input (and DISPLAY in environment). This must call xauth in that case.

The primary purpose of $HOME/.ssh/rc is to run any ini-

tialization routines that might be needed before the

user's home directory becomes accessible; AFS is a par-

ticular example of such an environment. If this file exists, it is run with /bin/sh after reading the environment files, but before starting the user's shell or command. It must not produce any output on stdout; stderr must be used instead. If X11 forwarding is in

use, it will receive the proto cookie pair in its stan-

dard input and DISPLAY in its environment. The script

must call xauth because sshd will not run xauth automat-

ically to add X11 cookies. This file will probably contain some initialization code followed by something similar to:

if read proto cookie && [ -n "$DISPLAY" ]

then

if [ `echo $DISPLAY | cut -c1-10` = 'localhost:' ]

then

# X11UseLocalhost=yes

echo add unix:`echo $DISPLAY |

cut -c11-` $proto $cookie

else

# X11UseLocalhost=no

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echo add $DISPLAY $proto $cookie

fi | xauth -q -

fi If this file does not exist, /etc/ssh/sshrc is run, and if that does not exist, xauth is used to store the

cookie. $HOME/.ssh/rc should be writable only by the

user, and need not be readable by anyone else. /etc/ssh/sshrc

Similar to $HOME/.ssh/rc. This can be used to specify

machine-specific login-time initializations globally.

This file should be writable only by root, and should be

world-readable.

SECURITY

sshd supports the use of several user authentication mechan-

isms: a public key system where keys are associated with

users (through users' authorized_keys files), a public key

system where keys are associated with hosts (see the Host-

basedAuthentication configuration parameter), a GSS-API

based method (see the GssAuthentication and GssKeyEx confi-

guration parameters) and three initial authentication

methods: none, password, and a generic prompt/reply proto-

col, keyboard-interactive.

sshd negotiates the use of the GSS-API with clients only if

it has a GSS-API acceptor credential for the "host" service.

This means that, for GSS-API based authentication, the

server must have a Kerberos V keytab entry (see below) or

the equivalent for any other GSS-API mechanism that might be

installed. In order for Kerberos authentication to work, a host/ Kerberos principal must exist for each Fully Qualified

Domain Name associated with the in.sshd server. Each of

these host/ principals must have a keytab entry in the

/etc/krb5/krb5.keytab file on the in.sshd server. An example

principal might be: host/bigmachine.eng.example.com See kadmin(1M) or gkadmin(1M) for instructions on adding a principal to a krb5.keytab file. See for a discussion of

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Kerberos authentication.

GSS-API authorization is covered in gss_auth_rules(5).

sshd uses pam(3PAM) for the three initial authentication

methods as well as for account management, session manage-

ment, and password management for all authentication methods.

Specifically, sshd calls pam_authenticate() for the "none,"

"password" and "keyboard-interactive" SSHv2 userauth types,

as well as for for the null and password authentication methods for SSHv1. Other SSHv2 authentication methods do not

call pam_authenticate(). pam_acct_mgmt() is called for each

authentication method that succeeds.

pam_setcred() and pam_open_session() are called when authen-

tication succeeds and pam_close_session() is called when

connections are closed.

pam_open_session() and pam_close_session() are also called

when SSHv2 channels with ptys are opened and closed. Each SSHv2 userauth type has its own PAM service name:

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____________________________________________________________

| SSHv2 Userauth | PAM Service Name |

|_____________________________|_____________________________|

| none | sshd-none |

|_____________________________|_____________________________|

| password | sshd-password |

|_____________________________|_____________________________|

| keyboard-interactive | sshd-kbdint |

|_____________________________|_____________________________|

| pubkey | sshd-pubkey |

|_____________________________|_____________________________|

| hostbased | sshd-hostbased |

|_____________________________|_____________________________|

| gssapi-with-mic | sshd-gssapi |

|_____________________________|_____________________________|

| gssapi-keyex | sshd-gssapi |

|_____________________________|_____________________________|

For SSHv1, sshd-v1 is always used.

If pam_acct_mgmt() returns PAM_NEW_AUTHTOK_REQD (indicating

that the user's authentication tokens have expired), then

sshd forces the use of "keyboard-interactive" userauth, if

version 2 of the protocol is in use. The "keyboard-

interactive" userauth will call pam_chauthtok() if

pam_acct_mgmt() once again returns PAM_NEW_AUTHTOK_REQD. By

this means, administrators are able to control what authen-

tication methods are allowed for SSHv2 on a per-user basis.

Setting up Host-based Authentication

To establish host-based authentication, you must perform the

following steps: o Configure the client. o Configure the server. o Publish known hosts. o Make appropriate entries in /etc/ssh/shosts.equiv and ~/.shosts. These steps are expanded in the following paragraphs.

o On a client machine, in the system-wide client con-

figuration file, /etc/ssh/ssh_config, you must have

the entry:

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System Administration Commands sshd(1M)

HostbasedAuthentication yes

See ssh_config(4) and ssh-keysign(1M).

o On the server, in the system-wide server configura-

tion file, /etc/ssh/sshd_config, you must have the

entry: HostbasedAuthentication yes

If per-user .shost files are to be allowed (see

last step), in the same file, you must have: IgnoreRhosts no

See sshd_config(4) for a description of these key-

words. o To publish known hosts, you must have entries for

the clients from which users will be allowed host-

based authentication. Make these entries in either

or both of the system-wide file

(/etc/ssh/ssh_known_hosts) or the per-user file

(~/.ssh/known_hosts).

o Note that sshd uses .shosts, not .rhosts. If you

want the functionality provided by .rhosts, but do not want to use rlogin or rsh because of their

security shortcomings, you can use .shosts in con-

junction with sshd. To use this feature, make

appropriate entries in /etc/ssh/shosts.equiv and ~/.shosts, in the format specified in rhosts(4). For the vast majority of network environments, .shosts is preferred over .rhosts.

ATTRIBUTES

See attributes(5) for descriptions of the following attri-

butes:

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System Administration Commands sshd(1M)

____________________________________________________________

| ATTRIBUTE TYPE | ATTRIBUTE VALUE |

|_____________________________|_____________________________|

| Availability | service/network/ssh |

|_____________________________|_____________________________|

| Interface Stability | Committed |

|_____________________________|_____________________________|

The interface stability of /etc/ssh/moduli is Private.

rhosts(4), ssh_config(4), sshd_config(4), attributes(5),

gss_auth_rules(5), kerberos(5), pam_roles(5), smf(5)

NOTES

The sshd service is managed by the service management facil-

ity, smf(5), under the service identifier: svc:/network/ssh:default Administrative actions on this service, such as enabling, disabling, or requesting restart, can be performed using svcadm(1M). The service's status can be queried using the svcs(1) command.

sshd always sets PAM_RHOST and sets PAM_AUSER in the case of

host-based userauth. This behavior allows for remote logins

to roles using host-based authentication. See pam_roles(5).

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