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NAME
sshd - OpenSSH SSH daemon
SYNOPSIS
sshd [-deiqD46] [-b bits] [-f config_file] [-g
login_grace_time] [-h host_key_file] [-k key_gen_time] [-p
port] [-u len] [-V client_protocol_id]
DESCRIPTION
sshd (SSH 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 is normally started at boot from /etc/rc. It
forks a new daemon for each incoming connection. The forked
daemons handle key exchange, encryption, authentication,
command execution, and data exchange. This implementation
of sshd supports both SSH protocol version 1 and 2 simul-
taneously. sshd works as follows.
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
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(8), rlogind(8), rexecd(8), and rexd(8)
are disabled (thus completely disabling rlogin(1) and rsh(1)
into the machine).
SSH protocol version 2
Version 2 works similarly: Each host has a host-specific
DSA key used to identify the host. However, when the daemon
starts, it does not generate a server key. Forward security
is provided 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, CAST128,
Arcfour, 192 bit AES, or 256 bit 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 (Pub-
keyAuthentication) or client host (HostbasedAuthentication)
authentication method, conventional password authentication
and challenge response based methods.
Command execution and data forwarding
If the client successfully authenticates itself, a dialog
for preparing the session is entered. At this time the
client may 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 forwarded to/from the shell or command on the server
side, and the user terminal in 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 a con-
figuration file. Command-line options override values
specified 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, ie. /usr/sbin/sshd.
The options are as follows:
-b bits
Specifies the number of bits in the ephemeral protocol
version 1 server key (default 768).
-d Debug mode. The server sends verbose debug output to
the system log, and does not put itself in the back-
ground. 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 debugging level. Maximum is 3.
-e When this option is specified, sshd will send the out-
put to the standard error instead of the system log.
-f configuration_file
Specifies the name of the configuration file. The
default is /usr/local/sparcv9/etc/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 (default 600 seconds). If the client fails to
authenticate the user within this many seconds, the
server disconnects and exits. A value of zero indi-
cates no limit.
-h host_key_file
Specifies the file from which the host key is read
(default /usr/local/sparcv9/etc/ssh_host_key ) . This
option must be given if sshd is not run as root (as the
normal host file is normally not readable by anyone but
root). It is possible to have multiple host key files
for the different protocol versions and host key algo-
rithms.
-i Specifies that sshd is being run from inetd. sshd is
normally not run from inetd because it needs to gen-
erate 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 (e.g., 512)
using sshd from inetd may be feasible.
-k key_gen_time
Specifies how often the ephemeral protocol version 1
server key is regenerated (default 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 regen-
erated.
-p port
Specifies the port on which the server listens for con-
nections (default 22).
-q Quiet mode. Nothing is sent to the system log. Nor-
mally the beginning, authentication, and termination of
each connection is logged.
-u len
This option is used to specify the size of the field in
the utmp structure that holds the remote host name. If
the resolved host name is longer than len , the dotted
decimal value will be used instead. This allows hosts
with very long host names that overflow this field to
still be uniquely identified. Specifying -u0 indicates
that only dotted decimal addresses should be put into
the utmp file.
-D When this option is specified sshd will 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.
CONFIGURATION FILE
sshd reads configuration data from
/usr/local/sparcv9/etc/sshd_config (or the file specified
with -f on the command line). The file contains keyword-
value pairs, one per line. Lines starting with `#' and
empty lines are interpreted as comments.
The following keywords are possible.
AFSTokenPassing
Specifies whether an AFS token may be forwarded to the
server. Default is ``yes''.
AllowGroups
This keyword can be followed by a list of group names,
separated by spaces. If specified, login is allowed
only for users whose primary group or supplementary
group list matches one of the patterns. `*' and `?'
can be used as wildcards in the patterns. Only group
names are valid; a numerical group ID isn't recognized.
By default login is allowed regardless of the group
list.
AllowTcpForwarding
Specifies whether TCP forwarding is permitted. The
default is ``yes''. Note that disabling TCP forwarding
does not improve security unless users are also denied
shell access, as they can always install their own for-
warders.
AllowUsers
This keyword can be followed by a list of user names,
separated by spaces. If specified, login is allowed
only for users names that match one of the patterns.
`*' and `?' can be used as wildcards in the patterns.
Only user names are valid; a numerical user ID isn't
recognized. By default login is allowed regardless of
the user name.
Banner
In some jurisdictions, sending a warning message before
authentication may be relevant for getting legal pro-
tection. The contents of the specified file are sent
to the remote user before authentication is allowed.
This option is only available for protocol version 2.
ChallengeResponseAuthentication
Specifies whether challenge response authentication is
allowed. Currently there is only support for skey(1)
authentication. The default is ``yes''.
Ciphers
Specifies the ciphers allowed for protocol version 2.
Multiple ciphers must be comma-separated. The default
is ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-
cbc,arcfour.''
CheckMail
Specifies whether sshd should check for new mail for
interactive logins. The default is ``no''.
ClientAliveInterval
Sets a timeout interval in seconds after which if no
data has been received from the client, sshd will send
a message through the encrypted channel to request a
response from the client. The default is 0, indicating
that these messages will not be sent to the client.
This option applies to protocol version 2 only.
ClientAliveCountMax
Sets the number of client alive messages (see above)
which may be sent without sshd receiving any messages
back from the client. If this threshold is reached
while client alive messages are being sent, sshd will
disconnect the client, terminating the session. It is
important to note that the use of client alive messages
is very different from Keepalive (below). The client
alive messages are sent through the encrypted channel
and therefore will not be spoofable. The TCP keepalive
option enabled by Keepalive is spoofable. You want to
use the client alive mechanism when you are basing
something important on clients having an active connec-
tion to the server.
The default value is 3. If you set ClientAliveInterval
(above) to 15, and leave this value at the default,
unresponsive ssh clients will be disconnected after
approximately 45 seconds.
DenyGroups
This keyword can be followed by a number of group
names, separated by spaces. Users whose primary group
or supplementary group list matches one of the patterns
aren't allowed to log in. `*' and `?' can be used as
wildcards in the patterns. Only group names are valid;
a numerical group ID isn't recognized. By default
login is allowed regardless of the group list.
DenyUsers
This keyword can be followed by a number of user names,
separated by spaces. Login is disallowed for user
names that match one of the patterns. `*' and `?' can
be used as wildcards in the patterns. Only user names
are valid; a numerical user ID isn't recognized. By
default login is allowed regardless of the user name.
GatewayPorts
Specifies whether remote hosts are allowed to connect
to ports forwarded for the client. The argument must
be ``yes'' or ``no''. The default is ``no''.
HostbasedAuthentication
Specifies whether rhosts or /etc/hosts.equiv authenti-
cation together with successful public key client host
authentication is allowed (hostbased authentication).
This option is similar to RhostsRSAAuthentication and
applies to protocol version 2 only. The default is
``no''.
HostKey
Specifies the file containing the private host keys
(default /usr/local/sparcv9/etc/ssh_host_key ) used by
SSH protocol versions 1 and 2. Note that sshd will
refuse to use a file if it is group/world-accessible.
It is possible to have multiple host key files.
``rsa1'' keys are used for version 1 and ``dsa'' or
``rsa'' are used for version 2 of the SSH protocol.
IgnoreRhosts
Specifies that .rhosts and .shosts files will not be
used in RhostsAuthentication , RhostsRSAAuthentication
or HostbasedAuthentication .
/etc/hosts.equiv and
/usr/local/sparcv9/etc/shosts.equiv are still used.
The default is ``yes''.
IgnoreUserKnownHosts
Specifies whether sshd should ignore the user's
$HOME/.ssh/known_hosts during RhostsRSAAuthentication
or HostbasedAuthentication . The default is ``no''.
KeepAlive
Specifies whether the system should send keepalive mes-
sages to the other side. If they are sent, death of
the connection or crash of one of the machines will be
properly noticed. However, this means that connections
will die if the route is down temporarily, and some
people find it annoying. On the other hand, if
keepalives are not sent, sessions may hang indefinitely
on the server, leaving ``ghost'' users and consuming
server resources.
The default is ``yes'' (to send keepalives), and the
server will notice if the network goes down or the
client host reboots. This avoids infinitely hanging
sessions.
To disable keepalives, the value should be set to
``no'' in both the server and the client configuration
files.
KerberosAuthentication
Specifies whether Kerberos authentication is allowed.
This can be in the form of a Kerberos ticket, or if
PasswordAuthentication is yes, the password provided by
the user will be validated through the Kerberos KDC.
To use this option, the server needs a Kerberos servtab
which allows the verification of the KDC's identity.
Default is ``yes''.
KerberosOrLocalPasswd
If set then if password authentication through Kerberos
fails then the password will be validated via any addi-
tional local mechanism such as /etc/passwd. Default is
``yes''.
KerberosTgtPassing
Specifies whether a Kerberos TGT may be forwarded to
the server. Default is ``no'', as this only works when
the Kerberos KDC is actually an AFS kaserver.
KerberosTicketCleanup
Specifies whether to automatically destroy the user's
ticket cache file on logout. Default is ``yes''.
KeyRegenerationInterval
In protocol version 1, the ephemeral server key is
automatically regenerated after this many seconds (if
it has been used). The purpose of regeneration is to
prevent decrypting captured sessions by later breaking
into the machine and stealing the keys. The key is
never stored anywhere. If the value is 0, the key is
never regenerated. The default is 3600 (seconds).
ListenAddress
Specifies the local addresses sshd should listen on.
The following forms may be used:
ListenAddress
host|IPv4_addr|IPv6_addr
ListenAddress
host|IPv4_addr:port
ListenAddress
[host|IPv6_addr]:port
If port is not specified, sshd will listen on the address
and all prior Port options specified. The default is to
listen on all local addresses. Multiple ListenAddress
options are permitted. Additionally, any Port options must
precede this option for non port qualified addresses. It
LoginGraceTime The server disconnects after this time if the
user has not successfully logged in. If the value is 0,
there is no time limit. The default is 600 (seconds). It
LogLevel Gives the verbosity level that is used when logging
messages from sshd. The possible values are: QUIET, FATAL,
ERROR, INFO, VERBOSE and DEBUG. The default is INFO. Log-
ging with level DEBUG violates the privacy of users and is
not recommended. It MACs Specifies the available MAC (mes-
sage authentication code) algorithms. The MAC algorithm is
used in protocol version 2 for data integrity protection.
Multiple algorithms must be comma-separated. The default is
Bd -literal
``hmac-md5,hmac-sha1,hmac-ripemd160,hmac-
ripemd160@openssh.com,
hmac-sha1-96,hmac-md5-96'' Ed It MaxStartups Specifies
the maximum number of concurrent unauthenticated connections
to the sshd daemon. Additional connections will be dropped
until authentication succeeds or the LoginGraceTime expires
for a connection. The default is 10.
Alternatively, random early drop can be enabled by specify-
ing the three colon separated values ``start:rate:full''
(e.g., "10:30:60"). sshd will refuse connection attempts
with a probability of ``rate/100'' (30%) if there are
currently ``start'' (10) unauthenticated connections. The
probability increases linearly and all connection attempts
are refused if the number of unauthenticated connections
reaches ``full'' (60). It PAMAuthenticationViaKbdInt Speci-
fies whether PAM challenge response authentication is
allowed. This allows the use of most PAM challenge response
authentication modules, but it will allow password authenti-
cation regardless of whether PasswordAuthentication is dis-
abled. The default is ``no''. It PasswordAuthentication
Specifies whether password authentication is allowed. The
default is ``yes''. It PermitEmptyPasswords When password
authentication is allowed, it specifies whether the server
allows login to accounts with empty password strings. The
default is ``no''. It PermitRootLogin Specifies whether
root can login using ssh(1). The argument must be ``yes'',
``without-password'', ``forced-commands-only'' or ``no''.
The default is ``yes''.
If this option is set to ``without-password'' password
authentication is disabled for root.
If this option is set to ``forced-commands-only'' root login
with public key authentication will be allowed, but only if
the command option has been specified (which may be useful
for taking remote backups even if root login is normally not
allowed). All other authentication methods are disabled for
root.
If this option is set to ``no'' root is not allowed to
login. It PidFile Specifies the file that contains the pro-
cess identifier of the sshd daemon. The default is
/var/run/sshd.pid. It Port Specifies the port number that
sshd listens on. The default is 22. Multiple options of
this type are permitted. See also ListenAddress . It
PrintLastLog Specifies whether sshd should print the date
and time when the user last logged in. The default is
``yes''. It PrintMotd Specifies whether sshd should print
/etc/motd when a user logs in interactively. (On some sys-
tems it is also printed by the shell, /etc/profile, or
equivalent.) The default is ``yes''. It Protocol Specifies
the protocol versions sshd should support. The possible
values are ``1'' and ``2''. Multiple versions must be
comma-separated. The default is ``2,1''. It PubkeyAuthen-
tication Specifies whether public key authentication is
allowed. The default is ``yes''. Note that this option
applies to protocol version 2 only. It ReverseMappingCheck
Specifies whether sshd should try to verify the remote host
name and check that the resolved host name for the remote IP
address maps back to the very same IP address. The default
is ``no''. It RhostsAuthentication Specifies whether
authentication using rhosts or /etc/hosts.equiv files is
sufficient. Normally, this method should not be permitted
because it is insecure. RhostsRSAAuthentication should be
used instead, because it performs RSA-based host authentica-
tion in addition to normal rhosts or /etc/hosts.equiv
authentication. The default is ``no''. This option applies
to protocol version 1 only. It RhostsRSAAuthentication
Specifies whether rhosts or /etc/hosts.equiv authentication
together with successful RSA host authentication is allowed.
The default is ``no''. This option applies to protocol ver-
sion 1 only. It RSAAuthentication Specifies whether pure
RSA authentication is allowed. The default is ``yes''.
This option applies to protocol version 1 only. It Ser-
verKeyBits Defines the number of bits in the ephemeral pro-
tocol version 1 server key. The minimum value is 512, and
the default is 768. It StrictModes Specifies whether sshd
should check file modes and ownership of the user's files
and home directory before accepting login. This is normally
desirable because novices sometimes accidentally leave their
directory or files world-writable. The default is ``yes''.
It Subsystem Configures an external subsystem (e.g., file
transfer daemon). Arguments should be a subsystem name and
a command to execute upon subsystem request. The command
sftp-server(8) implements the ``sftp'' file transfer subsys-
tem. By default no subsystems are defined. Note that this
option applies to protocol version 2 only. It SyslogFacil-
ity Gives the facility code that is used when logging mes-
sages from sshd. The possible values are: DAEMON, USER,
AUTH, LOCAL0, LOCAL1, LOCAL2, LOCAL3, LOCAL4, LOCAL5,
LOCAL6, LOCAL7. The default is AUTH. It UseLogin Specifies
whether login(1) is used for interactive login sessions.
Note that login(1) is never used for remote command execu-
tion. The default is ``no''. It X11DisplayOffset Specifies
the first display number available for sshd's X11 forward-
ing. This prevents sshd from interfering with real X11
servers. The default is 10. It X11Forwarding Specifies
whether X11 forwarding is permitted. The default is ``no''.
Note that disabling X11 forwarding does not improve security
in any way, as users can always install their own forward-
ers. It XAuthLocation Specifies the location of the
xauth(1) program. The default is /usr/openwin/bin/xauth.
LOGIN PROCESS
When a user successfully logs in, sshd does the following:
1. If the login is on a tty, and no command has been
specified, prints last login time and /etc/motd (unless
prevented in the configuration file or by
$HOME/.hushlogin ; see the FILES section).
2. If the login is on a tty, records login time.
3. Checks /etc/nologin ; if it exists, prints contents and
quits (unless root).
4. Changes to run with normal user privileges.
5. Sets up basic environment.
6. Reads $HOME/.ssh/environment if it exists.
7. Changes to user's home directory.
8. If $HOME/.ssh/rc exists, runs it; else if
/usr/local/sparcv9/etc/sshrc exists, runs it; otherwise
runs xauth. The ``rc'' files are given the X11 authen-
tication protocol and cookie in standard input.
9. Runs user's shell or command.
AUTHORIZED_KEYS FILE FORMAT
The $HOME/.ssh/authorized_keys file lists the RSA keys that
are permitted for RSA authentication in protocol version 1
Similarly, the $HOME/.ssh/authorized_keys2 file lists the
DSA and RSA keys that are permitted for public key authenti-
cation (PubkeyAuthentication) in protocol version 2.
Each line of the file contains one key (empty lines and
lines starting with a `#' are ignored as comments). Each
RSA public key consists of the following fields, separated
by spaces: options, bits, exponent, modulus, comment. Each
protocol version 2 public key consists of: options, key-
type, base64 encoded key, comment. The options fields are
optional; its presence is determined by whether the line
starts with a number or not (the option field never starts
with a number). The bits, exponent, modulus and comment
fields give the RSA key for protocol version 1; the comment
field is not used for anything (but may be convenient for
the user to identify the key). For protocol version 2 the
keytype is ``ssh-dss'' or ``ssh-rsa''.
Note that lines in this file are usually several hundred
bytes long (because of the size of the RSA key modulus).
You don't want to type them in; instead, copy the
identity.pub, id_dsa.pub or the id_rsa.pub file and edit it.
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:
from="pattern-list"
Specifies that in addition to RSA authentication, the
canonical name of the remote host must be present in
the comma-separated list of patterns (`*' and `?'
serve as wildcards). The list may also contain pat-
terns negated by prefixing them with `!' ; if the
canonical host name matches a negated pattern, the key
is not accepted. The purpose of this option is to
optionally increase security: RSA authentication by
itself does not trust the network or name servers or
anything (but the key); however, if somebody somehow
steals the key, the key permits an intruder to log in
from anywhere in the world. This additional option
makes using a stolen key more difficult (name servers
and/or 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 connection requests a pty; otherwise it is
run without a tty. Note that if you want a 8-bit clean
channel, you must not request a pty or should specify
no-pty . A quote may be included in the command by
quoting it with a backslash. This option might be use-
ful to restrict certain RSA keys to perform just a
specific operation. An example might be a key that
permits remote backups but nothing else. Note that the
client may specify TCP/IP and/or X11 forwarding unless
they are explicitly prohibited.
environment="NAME=value"
Specifies that the string 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.
no-port-forwarding
Forbids TCP/IP forwarding when this key is used for
authentication. Any port forward requests by the
client will return an error. This might be used, e.g.,
in connection with the command option.
no-X11-forwarding
Forbids X11 forwarding when this key is used for
authentication. 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 may
only connect to the specified host and port. Multiple
permitopen options may be applied separated by commas.
No pattern matching is performed on the specified host-
names, they must be literal domains or addresses.
Examples
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
permitopen="10.2.1.55:80",permitopen="10.2.1.56:25" 1024 33
23...2323
SSH_KNOWN_HOSTS FILE FORMAT
The /usr/local/sparcv9/etc/ssh_known_hosts,
/usr/local/sparcv9/etc/ssh_known_hosts2,
$HOME/.ssh/known_hosts, and $HOME/.ssh/known_hosts2 files
contain host public keys for all known hosts. The global
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.
Each line in these files contains the following fields:
hostnames, bits, exponent, modulus, comment. The fields are
separated by spaces.
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 may 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.
Bits, exponent, and modulus are taken directly from the RSA
host key; they can be obtained, e.g., from
/usr/local/sparcv9/etc/ssh_host_key.pub. The optional com-
ment field continues to the end of the line, and is not
used.
Lines starting with `#' and empty lines are ignored as com-
ments.
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 inev-
itably 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.
Note that the lines in these files are typically hundreds of
characters long, and you definitely don't want to type in
the host keys by hand. Rather, generate them by a script or
by taking /usr/local/sparcv9/etc/ssh_host_key.pub and adding
the host names at the front.
Examples
Bd -literal closenet,...,130.233.208.41 1024 37 159...93
closenet.hut.fi cvs.openbsd.org,199.185.137.3 ssh-rsa
AAAA1234.....= Ed
FILES
/usr/local/sparcv9/etc/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.
/usr/local/sparcv9/etc/ssh_host_dsa_key,
/usr/local/sparcv9/etc/ssh_host_rsa_key
/usr/local/sparcv9/etc/ssh_host_key,
These three files contain the private parts of the host
keys. These files should only be owned by root, read-
able only by root, and not accessible to others. Note
that sshd does not start if this file is group/world-
accessible.
/usr/local/sparcv9/etc/ssh_host_dsa_key.pub,
/usr/local/sparcv9/etc/ssh_host_rsa_key.pub
/usr/local/sparcv9/etc/ssh_host_key.pub,
These three files contain the public parts of the host
keys. These files should be world-readable but
writable only by root. Their contents should match the
respective private parts. These files are not really
used for anything; they are provided for the conveni-
ence of the user so their contents can be copied to
known hosts files. These files are created using ssh-
keygen(1).
/usr/local/sparcv9/etc/primes
Contains Diffie-Hellman groups used for the "Diffie-
Hellman Group Exchange".
/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.
$HOME/.ssh/authorized_keys
Lists the RSA keys that can be used to log into the
user's account. This file must be readable by root
(which may on some machines imply it being world-
readable if the user's home directory resides on an NFS
volume). It is recommended that it not be accessible
by others. The format of this file is described above.
Users will place the contents of their identity.pub
files into this file, as described in ssh-keygen(1).
$HOME/.ssh/authorized_keys2
Lists the public keys (RSA or DSA) that can be used to
log into the user's account. This file must be read-
able by root (which may on some machines imply it being
world-readable if the user's home directory resides on
an NFS volume). It is recommended that it not be
accessible by others. The format of this file is
described above. Users will place the contents of
their id_dsa.pub and/or id_rsa.pub files into this
file, as described in ssh-keygen(1).
/usr/local/sparcv9/etc/ssh_known_hosts and $HOME/.ssh/known_hosts
These files are consulted when using rhosts with RSA
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 it is connecting to the correct remote host.
These files should be writable only by root/the owner.
/usr/local/sparcv9/etc/ssh_known_hosts should be
world-readable, and $HOME/.ssh/known_hosts can but need
not be world-readable.
$HOME/.ssh/known_hosts2
/usr/local/sparcv9/etc/ssh_known_hosts2 and
These files are consulted when using protocol version 2
hostbased 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 it is connecting to the correct remote host.
These files should be writable only by root/the owner.
/usr/local/sparcv9/etc/ssh_known_hosts2 should be
world-readable, and $HOME/.ssh/known_hosts2 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.
/etc/hosts.allow, /etc/hosts.deny
If compiled with LIBWRAP support, tcp-wrappers access
controls may be defined here as described in
hosts_access(5).
$HOME/.rhosts
This file contains host-username pairs, separated by a
space, one per line. The given user on the correspond-
ing host is permitted to log in without password. The
same file is used by rlogind and rshd. The file must
be writable only by the user; it is recommended that it
not be accessible by others.
If is also possible to use netgroups 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
the simplest form, this file contains host names, one
per line. Users on those hosts are permitted to log in
without a password, provided they have the same user
name on both machines. The host name may also be fol-
lowed by a user name; such users are permitted to log
in as any user on this machine (except root). Addi-
tionally, the syntax ``+@group'' can be used to specify
netgroups. Negated entries start with `-'.
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 recommended 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. Using a user name practi-
cally grants the user root access. The only valid use
for user names that I can think of is in negative
entries.
Note that this warning also applies to rsh/rlogin.
/usr/local/sparcv9/etc/shosts.equiv
This is processed exactly as /etc/hosts.equiv. How-
ever, this file may 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 only contain 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.
$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(1) in that case.
The primary purpose of this file is to run any initial-
ization routines which may be needed before the user's
home directory becomes accessible; AFS is a particular
example of such an environment.
This file will probably contain some initialization
code followed by something similar to: Bd -literal
if read proto cookie; then echo add
$DISPLAY $proto $cookie | xauth -q - fi Ed
If this file does not exist,
/usr/local/sparcv9/etc/sshrc is run, and if that does
not exist either, xauth is used to store the cookie.
This file should be writable only by the user, and need
not be readable by anyone else.
/usr/local/sparcv9/etc/sshrc
Like $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.
AUTHORS
OpenSSH is a derivative of the original and free ssh 1.2.12
release by Tatu Ylonen. Aaron Campbell, Bob Beck, Markus
Friedl, Niels Provos, Theo de Raadt and Dug Song removed
many bugs, re-added newer features and created OpenSSH.
Markus Friedl contributed the support for SSH protocol ver-
sions 1.5 and 2.0.
SEE ALSO
scp(1), sftp(1), sftp-server(8), ssh(1), ssh-add(1), ssh-
agent(1), ssh-keygen(1), rlogin(1), rsh(1) Rs %A T. Ylonen
%A T. Kivinen %A M. Saarinen %A T. Rinne %A S. Lehtinen %T
"SSH Protocol Architecture" %N draft-ietf-secsh-
architecture-07.txt %D January 2001 %O work in progress
material Re Rs %A M. Friedl %A N. Provos %A W. A. Simpson %T
"Diffie-Hellman Group Exchange for the SSH Transport Layer
Protocol" %N draft-ietf-secsh-dh-group-exchange-00.txt %D
January 2001 %O work in progress material Re
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