diff options
Diffstat (limited to 'usr.bin/ssh')
| -rw-r--r-- | usr.bin/ssh/scp.1 | 29 | ||||
| -rw-r--r-- | usr.bin/ssh/ssh-agent.1 | 52 | ||||
| -rw-r--r-- | usr.bin/ssh/ssh-keygen.1 | 62 | ||||
| -rw-r--r-- | usr.bin/ssh/sshd.8 | 386 |
4 files changed, 316 insertions, 213 deletions
diff --git a/usr.bin/ssh/scp.1 b/usr.bin/ssh/scp.1 index d4c374e5f12..8e93e23d3fd 100644 --- a/usr.bin/ssh/scp.1 +++ b/usr.bin/ssh/scp.1 @@ -9,7 +9,7 @@ .\" .\" Created: Sun May 7 00:14:37 1995 ylo .\" -.\" $Id: scp.1,v 1.5 2000/01/04 16:57:16 markus Exp $ +.\" $Id: scp.1,v 1.6 2000/03/23 21:10:09 aaron Exp $ .\" .Dd September 25, 1999 .Dt SCP 1 @@ -38,7 +38,8 @@ .Sm on .Sh DESCRIPTION .Nm -copies files between hosts on a network. It uses +copies files between hosts on a network. +It uses .Xr ssh 1 for data transfer, and uses the same authentication and provides the same security as @@ -50,18 +51,19 @@ will ask for passwords or passphrases if they are needed for authentication. .Pp Any file name may contain a host and user specification to indicate -that the file is to be copied to/from that host. Copies between two -remote hosts are permitted. +that the file is to be copied to/from that host. +Copies between two remote hosts are permitted. .Pp The options are as follows: .Bl -tag -width Ds .It Fl c Ar cipher -Selects the cipher to use for encrypting the data transfer. This -option is directly passed to +Selects the cipher to use for encrypting the data transfer. +This option is directly passed to .Xr ssh 1 . .It Fl i Ar identity_file Selects the file from which the identity (private key) for RSA -authentication is read. This option is directly passed to +authentication is read. +This option is directly passed to .Xr ssh 1 . .It Fl p Preserves modification times, access times, and modes from the @@ -69,25 +71,28 @@ original file. .It Fl r Recursively copy entire directories. .It Fl v -Verbose mode. Causes +Verbose mode. +Causes .Nm and .Xr ssh 1 -to print debugging messages about their progress. This is helpful in +to print debugging messages about their progress. +This is helpful in debugging connection, authentication, and configuration problems. .It Fl B Selects batch mode (prevents asking for passwords or passphrases). .It Fl q Disables the progress meter. .It Fl C -Compression enable. Passes the +Compression enable. +Passes the .Fl C flag to .Xr ssh 1 to enable compression. .It Fl P Ar port -Specifies the port to connect to on the remote host. Note that this -option is written with a capital +Specifies the port to connect to on the remote host. +Note that this option is written with a capital .Sq P , because .Fl p diff --git a/usr.bin/ssh/ssh-agent.1 b/usr.bin/ssh/ssh-agent.1 index b98775d90bc..7029b60dcc4 100644 --- a/usr.bin/ssh/ssh-agent.1 +++ b/usr.bin/ssh/ssh-agent.1 @@ -1,4 +1,4 @@ -.\" $OpenBSD: ssh-agent.1,v 1.9 2000/01/22 02:17:50 aaron Exp $ +.\" $OpenBSD: ssh-agent.1,v 1.10 2000/03/23 21:10:10 aaron Exp $ .\" .\" -*- nroff -*- .\" @@ -27,12 +27,13 @@ .Oc .Sh DESCRIPTION .Nm -is a program to hold authentication private keys. The -idea is that +is a program to hold authentication private keys. +The idea is that .Nm is started in the beginning of an X-session or a login session, and all other windows or programs are started as clients to the ssh-agent -program. Through use of environment variables the agent can be located +program. +Through use of environment variables the agent can be located and automatically used for RSA authentication when logging in to other machines using .Xr ssh 1 . @@ -60,30 +61,34 @@ environment variable). If a commandline is given, this is executed as a subprocess of the agent. When the command dies, so does the agent. .Pp -The agent initially does not have any private keys. Keys are added -using +The agent initially does not have any private keys. +Keys are added using .Xr ssh-add 1 . When executed without arguments, .Xr ssh-add 1 adds the .Pa $HOME/.ssh/identity -file. If the identity has a passphrase, +file. +If the identity has a passphrase, .Xr ssh-add 1 asks for the passphrase (using a small X11 application if running -under X11, or from the terminal if running without X). It then sends -the identity to the agent. Several identities can be stored in the +under X11, or from the terminal if running without X). +It then sends the identity to the agent. +Several identities can be stored in the agent; the agent can automatically use any of these identities. .Ic ssh-add -l displays the identities currently held by the agent. .Pp The idea is that the agent is run in the user's local PC, laptop, or -terminal. Authentication data need not be stored on any other +terminal. +Authentication data need not be stored on any other machine, and authentication passphrases never go over the network. However, the connection to the agent is forwarded over SSH remote logins, and the user can thus use the privileges given by the identities anywhere in the network in a secure way. .Pp -There are two main ways to get an agent setup: Either you let the agent +There are two main ways to get an agent setup: +Either you let the agent start a new subcommand into which some environment variables are exported, or you let the agent print the needed shell commands (either .Xr sh 1 @@ -99,7 +104,8 @@ A unix-domain socket is created and the name of this socket is stored in the .Ev SSH_AUTH_SOCK environment -variable. The socket is made accessible only to the current user. +variable. +The socket is made accessible only to the current user. This method is easily abused by root or another instance of the same user. .Pp @@ -112,28 +118,30 @@ line terminates. .Sh FILES .Bl -tag -width Ds .It Pa $HOME/.ssh/identity -Contains the RSA authentication identity of the user. This file -should not be readable by anyone but the user. It is possible to +Contains the RSA authentication identity of the user. +This file should not be readable by anyone but the user. +It is possible to specify a passphrase when generating the key; that passphrase will be -used to encrypt the private part of this file. This file -is not used by +used to encrypt the private part of this file. +This file is not used by .Nm but is normally added to the agent using .Xr ssh-add 1 at login time. .It Pa /tmp/ssh-XXXX/agent.<pid> , Unix-domain sockets used to contain the connection to the -authentication agent. These sockets should only be readable by the -owner. The sockets should get automatically removed when the agent -exits. +authentication agent. +These sockets should only be readable by the owner. +The sockets should get automatically removed when the agent exits. .Sh AUTHOR Tatu Ylonen <ylo@cs.hut.fi> .Pp OpenSSH is a derivative of the original (free) ssh 1.2.12 release, but with bugs -removed and newer features re-added. Rapidly after the 1.2.12 release, -newer versions bore successively more restrictive licenses. This version -of OpenSSH +removed and newer features re-added. +Rapidly after the 1.2.12 release, +newer versions bore successively more restrictive licenses. +This version of OpenSSH .Bl -bullet .It has all components of a restrictive nature (i.e., patents, see diff --git a/usr.bin/ssh/ssh-keygen.1 b/usr.bin/ssh/ssh-keygen.1 index e7c837c79fb..90361643c7b 100644 --- a/usr.bin/ssh/ssh-keygen.1 +++ b/usr.bin/ssh/ssh-keygen.1 @@ -9,7 +9,7 @@ .\" .\" Created: Sat Apr 22 23:55:14 1995 ylo .\" -.\" $Id: ssh-keygen.1,v 1.11 2000/01/22 02:17:50 aaron Exp $ +.\" $Id: ssh-keygen.1,v 1.12 2000/03/23 21:10:10 aaron Exp $ .\" .Dd September 25, 1999 .Dt SSH-KEYGEN 1 @@ -48,27 +48,31 @@ key in Additionally, the system administrator may use this to generate host keys. .Pp Normally this program generates the key and asks for a file in which -to store the private key. The public key is stored in a file with the -same name but +to store the private key. +The public key is stored in a file with the same name but .Dq .pub -appended. The program also asks for a -passphrase. The passphrase may be empty to indicate no passphrase +appended. +The program also asks for a passphrase. +The passphrase may be empty to indicate no passphrase (host keys must have empty passphrase), or it may be a string of -arbitrary length. Good passphrases are 10-30 characters long and are +arbitrary length. +Good passphrases are 10-30 characters long and are not simple sentences or otherwise easily guessable (English prose has only 1-2 bits of entropy per word, and provides very bad -passphrases). The passphrase can be changed later by using the +passphrases). +The passphrase can be changed later by using the .Fl p option. .Pp -There is no way to recover a lost passphrase. If the passphrase is +There is no way to recover a lost passphrase. +If the passphrase is lost or forgotten, you will have to generate a new key and copy the corresponding public key to other machines. .Pp There is also a comment field in the key file that is only for -convenience to the user to help identify the key. The comment can -tell what the key is for, or whatever is useful. The comment is -initialized to +convenience to the user to help identify the key. +The comment can tell what the key is for, or whatever is useful. +The comment is initialized to .Dq user@host when the key is created, but can be changed using the .Fl c @@ -77,10 +81,11 @@ option. The options are as follows: .Bl -tag -width Ds .It Fl b Ar bits -Specifies the number of bits in the key to create. Minimum is 512 -bits. Generally 1024 bits is considered sufficient, and key sizes -above that no longer improve security but make things slower. The -default is 1024 bits. +Specifies the number of bits in the key to create. +Minimum is 512 bits. +Generally 1024 bits is considered sufficient, and key sizes +above that no longer improve security but make things slower. +The default is 1024 bits. .It Fl c Requests changing the comment in the private and public key files. The program will prompt for the file containing the private keys, for @@ -91,7 +96,8 @@ Specifies the filename of the key file. Show fingerprint of specified private or public key file. .It Fl p Requests changing the passphrase of a private key file instead of -creating a new private key. The program will prompt for the file +creating a new private key. +The program will prompt for the file containing the private key, for the old passphrase, and twice for the new passphrase. .It Fl q @@ -110,28 +116,30 @@ Provides the (old) passphrase. .Sh FILES .Bl -tag -width Ds .It Pa $HOME/.ssh/identity -Contains the RSA authentication identity of the user. This file -should not be readable by anyone but the user. It is possible to +Contains the RSA authentication identity of the user. +This file should not be readable by anyone but the user. +It is possible to specify a passphrase when generating the key; that passphrase will be -used to encrypt the private part of this file using 3DES. This file -is not automatically accessed by +used to encrypt the private part of this file using 3DES. +This file is not automatically accessed by .Nm but it is offered as the default file for the private key. .It Pa $HOME/.ssh/identity.pub -Contains the public key for authentication. The contents of this file -should be added to +Contains the public key for authentication. +The contents of this file should be added to .Pa $HOME/.ssh/authorized_keys on all machines -where you wish to log in using RSA authentication. There is no -need to keep the contents of this file secret. +where you wish to log in using RSA authentication. +There is no need to keep the contents of this file secret. .Sh AUTHOR Tatu Ylonen <ylo@cs.hut.fi> .Pp OpenSSH is a derivative of the original (free) ssh 1.2.12 release, but with bugs -removed and newer features re-added. Rapidly after the 1.2.12 release, -newer versions bore successively more restrictive licenses. This version -of OpenSSH +removed and newer features re-added. +Rapidly after the 1.2.12 release, +newer versions bore successively more restrictive licenses. +This version of OpenSSH .Bl -bullet .It has all components of a restrictive nature (i.e., patents, see diff --git a/usr.bin/ssh/sshd.8 b/usr.bin/ssh/sshd.8 index 66037320b8b..0ae2b3e5ee3 100644 --- a/usr.bin/ssh/sshd.8 +++ b/usr.bin/ssh/sshd.8 @@ -9,7 +9,7 @@ .\" .\" Created: Sat Apr 22 21:55:14 1995 ylo .\" -.\" $Id: sshd.8,v 1.35 2000/03/14 21:31:41 aaron Exp $ +.\" $Id: sshd.8,v 1.36 2000/03/23 21:10:10 aaron Exp $ .\" .Dd September 25, 1999 .Dt SSHD 8 @@ -33,39 +33,48 @@ .Xr ssh 1 . Together these programs replace rlogin and rsh programs, and provide secure encrypted communications between two untrusted hosts -over an insecure network. The programs are intended to be as easy to +over an insecure network. +The programs are intended to be as easy to install and use as possible. .Pp .Nm -is the daemon that listens for connections from clients. It is -normally started at boot from +is the daemon that listens for connections from clients. +It is normally started at boot from .Pa /etc/rc . It forks a new -daemon for each incoming connection. The forked daemons handle +daemon for each incoming connection. +The forked daemons handle key exchange, encryption, authentication, command execution, and data exchange. .Pp .Nm -works as follows. Each host has a host-specific RSA key -(normally 1024 bits) used to identify the host. Additionally, when +works as follows. +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. .Pp Whenever a client connects the daemon, the daemon sends its host -and server public keys to the client. The client compares the +and server public keys to the client. +The client compares the 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 +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 start to use this +the encrypted number to the server. +Both sides then start to 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 +communications in the session. +The rest of the session is encrypted using a conventional cipher, currently Blowfish and 3DES, with 3DES -being is used by default. The client selects the encryption algorithm +being is used by default. +The client selects the encryption algorithm to use from those offered by the server. .Pp -Next, the server and the client enter an authentication dialog. The -client tries to authenticate itself using +Next, the server and the client enter an authentication dialog. +The client tries to authenticate itself using .Pa .rhosts authentication, .Pa .rhosts @@ -75,7 +84,8 @@ based authentication. .Pp 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 +configuration file if desired. +System security is not improved unless .Xr rshd 8 , .Xr rlogind 8 , .Xr rexecd 8 , @@ -88,13 +98,15 @@ and into that machine). .Pp If the client successfully authenticates itself, a dialog for -preparing the session is entered. At this time the client may request +preparing the session is entered. +At this time the client may request things like allocating a pseudo-tty, forwarding X11 connections, forwarding TCP/IP connections, or forwarding the authentication agent connection over the secure channel. .Pp 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 +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. .Pp @@ -104,7 +116,8 @@ the client, and both sides exit. .Pp .Nm can be configured using command-line options or a configuration -file. Command-line options override values specified in the +file. +Command-line options override values specified in the configuration file. .Pp .Nm @@ -117,20 +130,23 @@ The options are as follows: Specifies the number of bits in the server key (default 768). .Pp .It Fl 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. +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. .It Fl f Ar configuration_file -Specifies the name of the configuration file. The default is +Specifies the name of the configuration file. +The default is .Pa /etc/sshd_config . .Nm refuses to start if there is no configuration file. .It Fl g Ar login_grace_time Gives the grace time for clients to authenticate themselves (default -300 seconds). If the client fails to authenticate the user within -this many seconds, the server disconnects and exits. A value of zero -indicates no limit. +300 seconds). +If the client fails to authenticate the user within +this many seconds, the server disconnects and exits. +A value of zero indicates no limit. .It Fl h Ar host_key_file Specifies the file from which the host key is read (default .Pa /etc/ssh_host_key ) . @@ -145,24 +161,28 @@ is being run from inetd. .Nm 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. +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 .Nm from inetd may be feasible. .It Fl k Ar key_gen_time Specifies how often the server key is regenerated (default 3600 -seconds, or one hour). The motivation for regenerating the key fairly +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. +seized. +A value of zero indicates that the key will never be regenerated. .It Fl p Ar port Specifies the port on which the server listens for connections (default 22). .It Fl q -Quiet mode. Nothing is sent to the system log. Normally the beginning, +Quiet mode. +Nothing is sent to the system log. +Normally the beginning, authentication, and termination of each connection is logged. .It Fl Q Do not print an error message if RSA support is missing. @@ -188,39 +208,43 @@ reads configuration data from .Pa /etc/sshd_config (or the file specified with .Fl f -on the command line). The file -contains keyword-value pairs, one per line. Lines starting with +on the command line). +The file contains keyword-value pairs, one per line. +Lines starting with .Ql # and empty lines are interpreted as comments. .Pp The following keywords are possible. .Bl -tag -width Ds .It Cm AFSTokenPassing -Specifies whether an AFS token may be forwarded to the server. Default is +Specifies whether an AFS token may be forwarded to the server. +Default is .Dq yes . .It Cm AllowGroups This keyword can be followed by a number of group names, separated -by spaces. If specified, login is allowed only for users whose primary +by spaces. +If specified, login is allowed only for users whose primary group matches one of the patterns. .Ql \&* and .Ql ? 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 primary group. +wildcards in the patterns. +Only group names are valid, a numerical group ID isn't recognized. +By default login is allowed regardless of the primary group. .Pp .It Cm AllowUsers This keyword can be followed by a number of user names, separated -by spaces. If specified, login is allowed only for users names that +by spaces. +If specified, login is allowed only for users names that match one of the patterns. .Ql \&* and .Ql ? 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. +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. .Pp .It Cm CheckMail Specifies whether @@ -230,27 +254,27 @@ The default is .Dq no . .It Cm DenyGroups This keyword can be followed by a number of group names, separated -by spaces. Users whose primary group matches one of the patterns +by spaces. +Users whose primary group matches one of the patterns aren't allowed to log in. .Ql \&* and .Ql ? 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 primary group. +wildcards in the patterns. +Only group names are valid, a numerical group ID isn't recognized. +By default login is allowed regardless of the primary group. .Pp .It Cm 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. +by spaces. +Login is disallowed for user names that match one of the patterns. .Ql \&* and .Ql ? -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. +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. .It Cm HostKey Specifies the file containing the private host key (default .Pa /etc/ssh_host_key ) . @@ -266,7 +290,8 @@ files will not be used in authentication. .Pa /etc/hosts.equiv and .Pa /etc/shosts.equiv -are still used. The default is +are still used. +The default is .Dq yes . .It Cm IgnoreUserKnownHosts Specifies whether @@ -279,10 +304,13 @@ The default is .Dq no . .It Cm KeepAlive Specifies whether the system should send keepalive messages 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 +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 send, +find it annoying. +On the other hand, if keepalives are not send, sessions may hang indefinitely on the server, leaving .Dq ghost users and consuming server resources. @@ -290,25 +318,27 @@ users and consuming server resources. The default is .Dq yes (to send keepalives), and the server will notice -if the network goes down or the client host reboots. This avoids -infinitely hanging sessions. +if the network goes down or the client host reboots. +This avoids infinitely hanging sessions. .Pp To disable keepalives, the value should be set to .Dq no in both the server and the client configuration files. .It Cm KerberosAuthentication -Specifies whether Kerberos authentication is allowed. This can -be in the form of a Kerberos ticket, or if +Specifies whether Kerberos authentication is allowed. +This can be in the form of a Kerberos ticket, or if .Cm PasswordAuthentication is yes, the password provided by the user will be validated through -the Kerberos KDC. Default is +the Kerberos KDC. +Default is .Dq yes . .It Cm KerberosOrLocalPasswd If set then if password authentication through Kerberos fails then the password will be validated via any additional local mechanism such as .Pa /etc/passwd -or SecurID. Default is +or SecurID. +Default is .Dq yes . .It Cm KerberosTgtPassing Specifies whether a Kerberos TGT may be forwarded to the server. @@ -317,15 +347,18 @@ Default is as this only works when the Kerberos KDC is actually an AFS kaserver. .It Cm KerberosTicketCleanup Specifies whether to automatically destroy the user's ticket cache -file on logout. Default is +file on logout. +Default is .Dq yes . .It Cm KeyRegenerationInterval The server key is automatically regenerated after this many seconds -(if it has been used). The purpose of regeneration is to prevent +(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). +stealing the keys. +The key is never stored anywhere. +If the value is 0, the key is never regenerated. +The default is 3600 (seconds). .It Cm ListenAddress Specifies what local address .Nm @@ -337,7 +370,8 @@ Additionally, the options must precede this option. .It Cm 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. +successfully logged in. +If the value is 0, there is no time limit. The default is 600 (seconds). .It Cm LogLevel Gives the verbosity level that is used when logging messages from @@ -353,8 +387,8 @@ The default is .Dq yes . .It Cm PermitEmptyPasswords When password authentication is allowed, it specifies whether the -server allows login to accounts with empty password strings. The default -is +server allows login to accounts with empty password strings. +The default is .Dq no . .It Cm PermitRootLogin Specifies whether the root can log in using @@ -379,24 +413,27 @@ normally not allowed). .It Cm Port Specifies the port number that .Nm -listens on. The default is 22. +listens on. +The default is 22. Multiple options of this type are permitted. .It Cm PrintMotd Specifies whether .Nm should print .Pa /etc/motd -when a user logs in interactively. (On some systems it is also -printed by the shell, +when a user logs in interactively. +(On some systems it is also printed by the shell, .Pa /etc/profile , -or equivalent.) The default is +or equivalent.) +The default is .Dq yes . .It Cm RandomSeed -Obsolete. Random number generation uses other techniques. +Obsolete. +Random number generation uses other techniques. .It Cm RhostsAuthentication Specifies whether authentication using rhosts or /etc/hosts.equiv -files is sufficient. Normally, this method should not be permitted -because it is insecure. +files is sufficient. +Normally, this method should not be permitted because it is insecure. .Cm RhostsRSAAuthentication should be used instead, because it performs RSA-based host authentication in addition @@ -405,18 +442,21 @@ The default is .Dq no . .It Cm RhostsRSAAuthentication Specifies whether rhosts or /etc/hosts.equiv authentication together -with successful RSA host authentication is allowed. The default is +with successful RSA host authentication is allowed. +The default is .Dq no . .It Cm RSAAuthentication -Specifies whether pure RSA authentication is allowed. The default is +Specifies whether pure RSA authentication is allowed. +The default is .Dq yes . .It Cm ServerKeyBits -Defines the number of bits in the server key. The minimum value is -512, and the default is 768. +Defines the number of bits in the server key. +The minimum value is 512, and the default is 768. .It Cm SkeyAuthentication Specifies whether .Xr skey 1 -authentication is allowed. The default is +authentication is allowed. +The default is .Dq yes . Note that s/key authentication is enabled only if .Cm PasswordAuthentication @@ -425,29 +465,34 @@ is allowed, too. Specifies whether .Nm 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 +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 .Dq yes . .It Cm SyslogFacility Gives the facility code that is used when logging messages from .Nm sshd . The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2, -LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. The default is AUTH. +LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. +The default is AUTH. .It Cm UseLogin Specifies whether .Xr login 1 -is used. The default is +is used. +The default is .Dq no . .It Cm X11DisplayOffset Specifies the first display number available for .Nm sshd Ns 's -X11 forwarding. This prevents +X11 forwarding. +This prevents .Nm from interfering with real X11 servers. The default is 10. .It Cm X11Forwarding -Specifies whether X11 forwarding is permitted. The default is +Specifies whether X11 forwarding is permitted. +The default is .Dq no . Note that disabling X11 forwarding does not improve security in any way, as users can always install their own forwarders. @@ -489,7 +534,8 @@ If exists, runs it; else if .Pa /etc/sshrc exists, runs -it; otherwise runs xauth. The +it; otherwise runs xauth. +The .Dq rc files are given the X11 authentication protocol and cookie in standard input. @@ -500,12 +546,15 @@ Runs user's shell or command. The .Pa $HOME/.ssh/authorized_keys file lists the RSA keys that are -permitted for RSA authentication. Each line of the file contains one +permitted for RSA authentication. +Each line of the file contains one key (empty lines and lines starting with a .Ql # are ignored as -comments). Each line consists of the following fields, separated by -spaces: options, bits, exponent, modulus, comment. The options field +comments). +Each line consists of the following fields, separated by +spaces: options, bits, exponent, modulus, comment. +The options field is 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; the @@ -513,47 +562,58 @@ comment field is not used for anything (but may be convenient for the user to identify the key). .Pp 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 +(because of the size of the RSA key modulus). +You don't want to type them in; instead, copy the .Pa identity.pub file and edit it. .Pp The options (if present) consists of comma-separated option -specifications. No spaces are permitted, except within double quotes. +specifications. +No spaces are permitted, except within double quotes. The following option specifications are supported: .Bl -tag -width Ds .It Cm 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 -patterns negated by prefixing them with '!'; if the canonical host -name matches a negated pattern, the key is not accepted. The purpose +patterns +.Pf ( Ql * +and +.Ql ? +serve as wildcards). +The list may also contain +patterns negated by prefixing them with +.Ql ! ; +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 +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). .It Cm 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. +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. A quote may be included in the -command by quoting it with a backslash. This option might be useful -to restrict certain RSA keys to perform just a specific operation. An -example might be a key that permits remote backups but nothing -else. Notice that the client may specify TCP/IP and/or X11 +otherwise it is run without a tty. +A quote may be included in the command by quoting it with a backslash. +This option might be useful +to restrict certain RSA keys to perform just a specific operation. +An example might be a key that permits remote backups but nothing else. +Notice that the client may specify TCP/IP and/or X11 forwardings unless they are explicitly prohibited. .It Cm environment="NAME=value" Specifies that the string is to be added to the environment when -logging in using this key. Environment variables set this way -override other default environment values. Multiple options of this -type are permitted. +logging in using this key. +Environment variables set this way +override other default environment values. +Multiple options of this type are permitted. .It Cm 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 +Any port forward requests by the client will return an error. +This might be used, e.g., in connection with the .Cm command option. .It Cm no-X11-forwarding @@ -576,19 +636,21 @@ The .Pa /etc/ssh_known_hosts and .Pa $HOME/.ssh/known_hosts -files contain host public keys for all known hosts. The global file should +files contain host public keys for all known hosts. +The global file should be prepared by the admistrator (optional), and the per-user file is maintained automatically: whenever the user connects an unknown host -its key is added to the per-user file. +its key is added to the per-user file. .Pp Each line in these files contains the following fields: hostnames, -bits, exponent, modulus, comment. The fields are separated by spaces. +bits, exponent, modulus, comment. +The fields are separated by spaces. .Pp 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 +name (when authenticating a server). +A pattern may also be preceded by .Ql ! to indicate negation: if the host name matches a negated pattern, it is not accepted (by that line) even if it matched another @@ -604,10 +666,13 @@ Lines starting with and empty lines are ignored as comments. .Pp When performing host authentication, authentication is accepted if any -matching line has the proper key. It is thus permissible (but not +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 +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. .Pp @@ -636,7 +701,9 @@ does not start if this file is group/world-accessible. .It Pa /etc/ssh_host_key.pub 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 +root. +Its contents should match the private part. +This file is not really used for anything; it is only provided for the convenience of the user so its contents can be copied to known hosts files. These two files are created using @@ -646,21 +713,22 @@ Contains the process ID of the .Nm listening for connections (if there are several daemons running concurrently for different ports, this contains the pid of the one -started last). The contents of this file are not sensitive; it can be -world-readable. +started last). +The contents of this file are not sensitive; it can be world-readable. .It Pa $HOME/.ssh/authorized_keys Lists the RSA keys that can be used to log into the user's account. This file must be readable by root (which may on some machines imply it being world-readable if the user's home directory resides on an NFS -volume). It is recommended that it not be accessible by others. The -format of this file is described above. +volume). +It is recommended that it not be accessible by others. +The format of this file is described above. .It Pa "/etc/ssh_known_hosts" and "$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. +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 we intended to -connect. These files should be writable only by root/the owner. +to verify that the remote host is the one we intended to connect. +These files should be writable only by root/the owner. .Pa /etc/ssh_known_hosts should be world-readable, and .Pa $HOME/.ssh/known_hosts @@ -668,9 +736,11 @@ can but need not be world-readable. .It Pa /etc/nologin If this file exists, .Nm -refuses to let anyone except root log in. The contents of the file +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. +refused. +The file should be world-readable. .It Pa /etc/hosts.allow, /etc/hosts.deny If compiled with .Sy LIBWRAP @@ -678,13 +748,16 @@ support, tcp-wrappers access controls may be defined here as described in .Xr hosts_access 5 . .It Pa $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. +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 writable only by the user; it is recommended that it not be accessible by others. .Pp -If is also possible to use netgroups in the file. Either host or user +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. .It Pa $HOME/.shosts @@ -696,21 +769,26 @@ not used by rlogin and rshd, so using this permits access using SSH only. .Pa /etc/hosts.equiv This file is used during .Pa .rhosts -authentication. In the -simplest form, this file contains host names, one per line. Users on +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 +have the same user name on both machines. +The host name may also be followed by a user name; such users are permitted to log in as .Em any -user on this machine (except root). Additionally, the syntax +user on this machine (except root). +Additionally, the syntax .Dq +@group -can be used to specify netgroups. Negated entries start with +can be used to specify netgroups. +Negated entries start with .Ql \&- . .Pp 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 +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. .Pp .Sy "Warning: It is almost never a good idea to use user names in" @@ -718,8 +796,9 @@ that it be world-readable. Beware that it really means that the named user(s) can log in as .Em anybody , which includes bin, daemon, adm, and other accounts that own critical -binaries and directories. Using a user name practically grants the -user root access. The only valid use for user names that I can think +binaries and directories. +Using a user name practically grants the user root access. +The only valid use for user names that I can think of is in negative entries. .Pp Note that this warning also applies to rsh/rlogin. @@ -729,18 +808,20 @@ This is processed exactly as However, this file may be useful in environments that want to run both rsh/rlogin and ssh. .It Pa $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 +This file is read into the environment at login (if it exists). +It can only contain empty lines, comment lines (that start with .Ql # ) , -and assignment lines of the form name=value. The file should be writable +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. .It Pa $HOME/.ssh/rc If this file exists, it is run with /bin/sh after reading 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 +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 .Ev DISPLAY -in environment). This must call +in environment). +This must call .Xr xauth 1 in that case. .Pp @@ -763,12 +844,13 @@ readable by anyone else. Like .Pa $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. +machine-specific login-time initializations globally. +This file should be writable only by root, and should be world-readable. .Sh AUTHOR OpenSSH is a derivative of the original (free) ssh 1.2.12 release by Tatu Ylonen, -but with bugs removed and newer features re-added. Rapidly after the +but with bugs removed and newer features re-added. +Rapidly after the 1.2.12 release, newer versions of the original ssh bore successively more restrictive licenses, and thus demand for a free version was born. This version of OpenSSH |