sftp-server

package: openssh-server

title: sftp-server(8)

summary: OpenSSH SFTP server subsystem

text:
# sftp-server(8)

## NAME
sftp-server — OpenSSH SFTP server subsystem

## SYNOPSIS
sftp-server

[-ehR] [-d start_directory] [-f log_facility] [-l log_level] [-P denied_requests] [-p allowed_requests] [-u umask]

sftp-server

-Q protocol_feature

## DESCRIPTION
sftp-server is a program that speaks the server side of SFTP protocol to stdout and expects client requests from stdin. sftp-server is not intended to be called directly, but from sshd(8) using the Subsystem option.

Command-line flags to sftp-server should be specified in the Subsystem declaration. See sshd_config(5) for more information.

Valid options are:

-d start_directory

Specifies an alternate starting directory for users. The pathname may contain the following tokens that are expanded at runtime: %% is replaced by a literal '%', %d is replaced by the home directory of the user being authenticated, and %u is replaced by the username of that user. The default is to use the user's home directory. This option is useful in conjunction with the sshd_config(5) ChrootDirectory option.

-e

Causes sftp-server to print logging information to stderr instead of syslog for debugging.

-f log_facility

Specifies the facility code that is used when logging messages from sftp-server. The possible values are: DAEMON, USER, AUTH, AUTHPRIV, LOCAL0, LOCAL1, LOCAL2, LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. The default is AUTHPRIV.

-h

Displays sftp-server usage information.

-l log_level

Specifies which messages will be logged by sftp-server. The possible values are: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. INFO and VERBOSE log transactions that sftp-server performs on behalf of the client. DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify higher levels of debugging output. The default is ERROR.

-P denied_requests

Specifies a comma-separated list of SFTP protocol requests that are banned by the server. sftp-server will reply to any denied request with a failure. The -Q flag can be used to determine the supported request types. If both denied and allowed lists are specified, then the denied list is applied before the allowed list.

-p allowed_requests

Specifies a comma-separated list of SFTP protocol requests that are permitted by the server. All request types that are not on the allowed list will be logged and replied to with a failure message. Care must be taken when using this feature to ensure that requests made implicitly by SFTP clients are permitted.

-Q protocol_feature

Queries protocol features supported by sftp-server. At present the only feature that may be queried is “requests”, which may be used to deny or allow specific requests (flags -P and -p respectively).

-R

Places this instance of sftp-server into a read-only mode. Attempts to open files for writing, as well as other operations that change the state of the filesystem, will be denied.

-u umask

Sets an explicit umask(2) to be applied to newly-created files and directories, instead of the user's default mask.

On some systems, sftp-server must be able to access /dev/log for logging to work, and use of sftp-server in a chroot configuration therefore requires that syslogd(8) establish a logging socket inside the chroot directory.

## SEE ALSO
sftp(1), ssh(1), sshd_config(5), sshd(8)

T. Ylonen and S. Lehtinen, SSH File Transfer Protocol, draft-ietf-secsh-filexfer-02.txt, October 2001, work in progress material.

## HISTORY
sftp-server first appeared in OpenBSD 2.8.

## AUTHORS
Markus Friedl <markus@openbsd.org>


sshd

title: sshd(8)

summary: OpenSSH daemon

text:
# sshd(8)

## NAME
sshd — OpenSSH daemon

## SYNOPSIS
sshd

[-46DdeGiqTtV] [-C connection_spec] [-c host_certificate_file] [-E log_file] [-f config_file] [-g login_grace_time] [-h host_key_file] [-o option] [-p port] [-u len]

## DESCRIPTION
sshd (OpenSSH Daemon) is the daemon program for ssh(1). It provides secure encrypted communications between two untrusted hosts over an insecure network.

sshd 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.

sshd can be configured using command-line options or a configuration file (by default sshd_config(5)); 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 and options it was started with, e.g. /usr/sbin/sshd.

The options are as follows:

-4

Forces sshd to use IPv4 addresses only.

-6

Forces sshd to use IPv6 addresses only.

-C connection_spec

Specify the connection parameters to use for the -T extended test mode. If provided, any Match directives in the configuration file that would apply are applied before the configuration is written to standard output. The connection parameters are supplied as keyword=value pairs and may be supplied in any order, either with multiple -C options or as a comma-separated list. The keywords are “addr”, “user”, “host”, “laddr”, “lport”, and “rdomain” and correspond to source address, user, resolved source host name, local address, local port number and routing domain respectively.

-c host_certificate_file

Specifies a path to a certificate file to identify sshd during key exchange. The certificate file must match a host key file specified using the -h option or the HostKey configuration directive.

-D

When this option is specified, sshd will not detach and does not become a daemon. This allows easy monitoring of sshd.

-d

Debug mode. The server sends verbose debug output to standard error, and does not put itself in the background. The server also will not fork(2) 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 log_file

Append debug logs to log_file instead of the system log.

-e

Write debug logs to standard error instead of the system log.

-f config_file

Specifies the name of the configuration file. The default is /etc/openssh/sshd_config. sshd refuses to start if there is no configuration file.

-G

Parse and print configuration file. Check the validity of the configuration file, output the effective configuration to stdout and then exit. Optionally, Match rules may be applied by specifying the connection parameters using one or more -C options.

-g login_grace_time

Gives the grace time for clients to authenticate themselves (default 120 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.

-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 anyone but root). The default is /etc/openssh/ssh_host_ecdsa_key, /etc/openssh/ssh_host_ed25519_key and /etc/openssh/ssh_host_rsa_key. It is possible to have multiple host key files for the different host key algorithms.

-i

Specifies that sshd is being run from inetd(8).

-o option

Can be used to give options in the format used in the configuration file. This is useful for specifying options for which there is no separate command-line flag. For full details of the options, and their values, see sshd_config(5).

-p port

Specifies the port on which the server listens for connections (default 22). Multiple port options are permitted. Ports specified in the configuration file with the Port option are ignored when a command-line port is specified. Ports specified using the ListenAddress option override command-line ports.

-q

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

-T

Extended test mode. Check the validity of the configuration file, output the effective configuration to stdout and then exit. Optionally, Match rules may be applied by specifying the connection parameters using one or more -C options. This is similar to the -G flag, but it includes the additional testing performed by the -t flag.

-t

Test mode. Only check the validity of the configuration file and sanity of the keys. This is useful for updating sshd reliably as configuration options may change.

-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. -u0 may also be used to prevent sshd from making DNS requests unless the authentication mechanism or configuration requires it. Authentication mechanisms that may require DNS include HostbasedAuthentication and using a from="pattern-list" option in a key file. Configuration options that require DNS include using a USER@HOST pattern in AllowUsers or DenyUsers.

-V

Display the version number and exit.

## AUTHENTICATION
The OpenSSH SSH daemon supports SSH protocol 2 only. Each host has a host-specific key, used to identify the host. Whenever a client connects, the daemon responds with its public host key. The client compares the host key against its own database to verify that it has not changed. Forward secrecy 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. 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 (MAC).

Finally, the server and the client enter an authentication dialog. The client tries to authenticate itself using host-based authentication, public key authentication, challenge-response authentication, or password authentication.

Regardless of the authentication type, the account is checked to ensure that it is accessible. An account is not accessible if it is locked, listed in DenyUsers or its group is listed in DenyGroups . The definition of a locked account is system dependent. Some platforms have their own account database (eg AIX) and some modify the passwd field ( ‘*LK*’ on Solaris and UnixWare, ‘*’ on HP-UX, containing ‘Nologin’ on Tru64, a leading ‘*LOCKED*’ on FreeBSD and a leading ‘!’ on most Linuxes). If there is a requirement to disable password authentication for the account while allowing still public-key, then the passwd field should be set to something other than these values (eg ‘NP’ or ‘*NP*’ ).

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, forwarding X11 connections, forwarding TCP connections, or forwarding the authentication agent connection over the secure channel.

After this, the client either requests an interactive shell or execution of a non-interactive command, which sshd will execute via the user's shell using its -c option. 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.

## LOGIN PROCESS
When a user successfully logs in, sshd does the following:

- 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 ~/.hushlogin; see the FILES section).

- If the login is on a tty, records login time.

- Checks /etc/nologin; if it exists, prints contents and quits (unless root).

- Changes to run with normal user privileges.

- Sets up basic environment.

- Reads the file ~/.ssh/environment, if it exists, and users are allowed to change their environment. See the PermitUserEnvironment option in sshd_config(5).

- Changes to user's home directory.

- If ~/.ssh/rc exists and the sshd_config(5) PermitUserRC option is set, runs it; else if /etc/openssh/sshrc exists, runs it; otherwise runs xauth(1). The “rc” files are given the X11 authentication protocol and cookie in standard input. See SSHRC, below.

- Runs user's shell or command. All commands are run under the user's login shell as specified in the system password database.

## SSHRC
If the file ~/.ssh/rc exists, sh(1) runs it 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 standard input (and DISPLAY in its environment). The script must call xauth(1) because sshd will not run xauth automatically to add X11 cookies.

The primary purpose of this file is to run any initialization 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:

```
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
		echo add $DISPLAY $proto $cookie
	fi | xauth -q -
fi
```

If this file does not exist, /etc/openssh/sshrc is run, and if that does not exist either, xauth is used to add the cookie.

## AUTHORIZED_KEYS FILE FORMAT
AuthorizedKeysFile specifies the files containing public keys for public key authentication; if this option is not specified, the default is ~/.ssh/authorized_keys and ~/.ssh/authorized_keys2. Each line of the file contains one key (empty lines and lines starting with a ‘#’ are ignored as comments). Public keys consist of the following space-separated fields: options, keytype, base64-encoded key, comment. The options field is optional. The supported key types are:

- sk-ecdsa-sha2-nistp256@openssh.com

- ecdsa-sha2-nistp256

- ecdsa-sha2-nistp384

- ecdsa-sha2-nistp521

- sk-ssh-ed25519@openssh.com

- ssh-ed25519

- ssh-dss

- ssh-rsa

The comment field is not used for anything (but may be convenient for the user to identify the key).

Note that lines in this file can be several hundred bytes long (because of the size of the public key encoding) up to a limit of 8 kilobytes, which permits RSA keys up to 16 kilobits. You don't want to type them in; instead, copy the id_dsa.pub, id_ecdsa.pub, id_ecdsa_sk.pub, id_ed25519.pub, id_ed25519_sk.pub, or the id_rsa.pub file and edit it.

sshd enforces a minimum RSA key modulus size of 1024 bits.

The options (if present) consist of comma-separated option specifications. No spaces are permitted, except within double quotes. The following option specifications are supported (note that option keywords are case-insensitive):

agent-forwarding

Enable authentication agent forwarding previously disabled by the restrict option.

cert-authority

Specifies that the listed key is a certification authority (CA) that is trusted to validate signed certificates for user authentication. Certificates may encode access restrictions similar to these key options. If both certificate restrictions and key options are present, the most restrictive union of the two is applied.

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. A quote may be included in the command by quoting it with a backslash. This option might be useful to restrict certain public 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 and/or X11 forwarding unless they are explicitly prohibited, e.g. using the restrict key option.

The command originally supplied by the client is available in the SSH_ORIGINAL_COMMAND environment variable. Note that this option applies to shell, command or subsystem execution. Also note that this command may be superseded by a sshd_config(5) ForceCommand directive.

If a command is specified and a forced-command is embedded in a certificate used for authentication, then the certificate will be accepted only if the two commands are identical.

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. Environment processing is disabled by default and is controlled via the PermitUserEnvironment option.

expiry-time="timespec"

Specifies a time after which the key will not be accepted. The time may be specified as a YYYYMMDD[Z] date or a YYYYMMDDHHMM[SS][Z] time. Dates and times will be interpreted in the system time zone unless suffixed by a Z character, in which case they will be interpreted in the UTC time zone.

from="pattern-list"

Specifies that in addition to public key authentication, either the canonical name of the remote host or its IP address must be present in the comma-separated list of patterns. See PATTERNS in ssh_config(5) for more information on patterns. In addition to the wildcard matching that may be applied to hostnames or addresses, a from stanza may match IP addresses using CIDR address/masklen notation.

The purpose of this option is to optionally increase security: public key 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).

no-agent-forwarding

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

no-port-forwarding

Forbids TCP 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-pty

Prevents tty allocation (a request to allocate a pty will fail).

no-user-rc

Disables execution of ~/.ssh/rc.

no-X11-forwarding

Forbids X11 forwarding when this key is used for authentication. Any X11 forward requests by the client will return an error.

permitlisten="[host:]port"

Limit remote port forwarding with the ssh(1) -R option such that it may only listen on the specified host (optional) and port. IPv6 addresses can be specified by enclosing the address in square brackets. Multiple permitlisten options may be applied separated by commas. Hostnames may include wildcards as described in the PATTERNS section in ssh_config(5). A port specification of * matches any port. Note that the setting of GatewayPorts may further restrict listen addresses. Note that ssh(1) will send a hostname of “localhost” if a listen host was not specified when the forwarding was requested, and that this name is treated differently to the explicit localhost addresses “127.0.0.1” and “::1”.

permitopen="host:port"

Limit local port forwarding with the ssh(1) -L option such that it may only connect to the specified host and port. IPv6 addresses can be specified by enclosing the address in square brackets. Multiple permitopen options may be applied separated by commas. No pattern matching or name lookup is performed on the specified hostnames, they must be literal host names and/or addresses. A port specification of * matches any port.

port-forwarding

Enable port forwarding previously disabled by the restrict option.

principals="principals"

On a cert-authority line, specifies allowed principals for certificate authentication as a comma-separated list. At least one name from the list must appear in the certificate's list of principals for the certificate to be accepted. This option is ignored for keys that are not marked as trusted certificate signers using the cert-authority option.

pty

Permits tty allocation previously disabled by the restrict option.

no-touch-required

Do not require demonstration of user presence for signatures made using this key. This option only makes sense for the FIDO authenticator algorithms ecdsa-sk and ed25519-sk.

verify-required

Require that signatures made using this key attest that they verified the user, e.g. via a PIN. This option only makes sense for the FIDO authenticator algorithms ecdsa-sk and ed25519-sk.

restrict

Enable all restrictions, i.e. disable port, agent and X11 forwarding, as well as disabling PTY allocation and execution of ~/.ssh/rc. If any future restriction capabilities are added to authorized_keys files, they will be included in this set.

tunnel="n"

Force a tun(4) device on the server. Without this option, the next available device will be used if the client requests a tunnel.

user-rc

Enables execution of ~/.ssh/rc previously disabled by the restrict option.

X11-forwarding

Permits X11 forwarding previously disabled by the restrict option.

An example authorized_keys file:

```
# Comments are allowed at start of line. Blank lines are allowed.
# Plain key, no restrictions
ssh-rsa ...
# Forced command, disable PTY and all forwarding
restrict,command="dump /home" ssh-rsa ...
# Restriction of ssh -L forwarding destinations
permitopen="192.0.2.1:80",permitopen="192.0.2.2:25" ssh-rsa ...
# Restriction of ssh -R forwarding listeners
permitlisten="localhost:8080",permitlisten="[::1]:22000" ssh-rsa ...
# Configuration for tunnel forwarding
tunnel="0",command="sh /etc/netstart tun0" ssh-rsa ...
# Override of restriction to allow PTY allocation
restrict,pty,command="nethack" ssh-rsa ...
# Allow FIDO key without requiring touch
no-touch-required sk-ecdsa-sha2-nistp256@openssh.com ...
# Require user-verification (e.g. PIN or biometric) for FIDO key
verify-required sk-ecdsa-sha2-nistp256@openssh.com ...
# Trust CA key, allow touch-less FIDO if requested in certificate
cert-authority,no-touch-required,principals="user_a" ssh-rsa ...
```

## SSH_KNOWN_HOSTS FILE FORMAT
The /etc/openssh/ssh_known_hosts and ~/.ssh/known_hosts 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 to an unknown host, its key is added to the per-user file.

Each line in these files contains the following fields: marker (optional), hostnames, keytype, base64-encoded key, comment. The fields are separated by spaces.

The marker is optional, but if it is present then it must be one of “@cert-authority”, to indicate that the line contains a certification authority (CA) key, or “@revoked”, to indicate that the key contained on the line is revoked and must not ever be accepted. Only one marker should be used on a key line.

Hostnames is a comma-separated list of patterns (‘*’ and ‘?’ act as wildcards); each pattern in turn is matched against the host name. When sshd is authenticating a client, such as when using HostbasedAuthentication, this will be the canonical client host name. When ssh(1) is authenticating a server, this will be the host name given by the user, the value of the ssh(1) HostkeyAlias if it was specified, or the canonical server hostname if the ssh(1) CanonicalizeHostname option was used.

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 pattern on the line. A hostname or address may optionally be enclosed within ‘[’ and ‘]’ brackets then followed by ‘:’ and a non-standard port number.

Alternately, hostnames may be stored in a hashed form which hides host names and addresses should the file's contents be disclosed. Hashed hostnames start with a ‘|’ character. Only one hashed hostname may appear on a single line and none of the above negation or wildcard operators may be applied.

The keytype and base64-encoded key are taken directly from the host key; they can be obtained, for example, from /etc/openssh/ssh_host_rsa_key.pub. The optional comment field continues to the end of the line, and is not used.

Lines starting with ‘#’ and empty lines are ignored as comments.

When performing host authentication, authentication is accepted if any matching line has the proper key; either one that matches exactly or, if the server has presented a certificate for authentication, the key of the certification authority that signed the certificate. For a key to be trusted as a certification authority, it must use the “@cert-authority” marker described above.

The known hosts file also provides a facility to mark keys as revoked, for example when it is known that the associated private key has been stolen. Revoked keys are specified by including the “@revoked” marker at the beginning of the key line, and are never accepted for authentication or as certification authorities, but instead will produce a warning from ssh(1) when they are encountered.

It is 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.

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, ssh-keyscan(1) or by taking, for example, /etc/openssh/ssh_host_rsa_key.pub and adding the host names at the front. ssh-keygen(1) also offers some basic automated editing for ~/.ssh/known_hosts including removing hosts matching a host name and converting all host names to their hashed representations.

An example ssh_known_hosts file:

```
# Comments allowed at start of line
cvs.example.net,192.0.2.10 ssh-rsa AAAA1234.....=
# A hashed hostname
|1|JfKTdBh7rNbXkVAQCRp4OQoPfmI=|USECr3SWf1JUPsms5AqfD5QfxkM= ssh-rsa
AAAA1234.....=
# A revoked key
@revoked * ssh-rsa AAAAB5W...
# A CA key, accepted for any host in *.mydomain.com or *.mydomain.org
@cert-authority *.mydomain.org,*.mydomain.com ssh-rsa AAAAB5W...
```

## FILES
~/.hushlogin

This file is used to suppress printing the last login time and /etc/motd, if PrintLastLog and PrintMotd, respectively, are enabled. It does not suppress printing of the banner specified by Banner.

~/.rhosts

This file is used for host-based authentication (see ssh(1) for more information). On some machines this file may need to be world-readable if the user's home directory is on an NFS partition, because sshd reads it as root. Additionally, this file must be owned by the user, and must not have write permissions for anyone else. The recommended permission for most machines is read/write for the user, and not accessible by others.

~/.shosts

This file is used in exactly the same way as .rhosts, but allows host-based authentication without permitting login with rlogin/rsh.

~/.ssh/

This directory is the default location for all user-specific configuration and authentication information. There is no general requirement to keep the entire contents of this directory secret, but the recommended permissions are read/write/execute for the user, and not accessible by others.

~/.ssh/authorized_keys

Lists the public keys (DSA, ECDSA, Ed25519, RSA) that can be used for logging in as this user. The format of this file is described above. The content of the file is not highly sensitive, but the recommended permissions are read/write for the user, and not accessible by others. If this file, the ~/.ssh directory, or the user's home directory are writable by other users, then the file could be modified or replaced by unauthorized users. In this case, sshd will not allow it to be used unless the StrictModes option has been set to “no”.

~/.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. Environment processing is disabled by default and is controlled via the PermitUserEnvironment option.

~/.ssh/known_hosts

Contains a list of host keys for all hosts the user has logged into that are not already in the systemwide list of known host keys. The format of this file is described above. This file should be writable only by root/the owner and can, but need not be, world-readable.

~/.ssh/rc

Contains initialization routines to be run before the user's home directory becomes accessible. This file should be writable only by the user, and need not be readable by anyone else.

/etc/hosts.equiv

This file is for host-based authentication (see ssh(1)). It should only be writable by root.

/etc/openssh/moduli

Contains Diffie-Hellman groups used for the "Diffie-Hellman Group Exchange" key exchange method. The file format is described in moduli(5). If no usable groups are found in this file then fixed internal groups will be used.

/etc/motd

See motd(5).

/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/openssh/shosts.equiv

This file is used in exactly the same way as hosts.equiv, but allows host-based authentication without permitting login with rlogin/rsh.

/etc/openssh/ssh_host_ecdsa_key

/etc/openssh/ssh_host_ed25519_key

/etc/openssh/ssh_host_rsa_key

These files contain the private parts of the host keys. These files should only be owned by root, readable only by root, and not accessible to others. Note that sshd does not start if these files are group/world-accessible.

/etc/openssh/ssh_host_ecdsa_key.pub

/etc/openssh/ssh_host_ed25519_key.pub

/etc/openssh/ssh_host_rsa_key.pub

These 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 convenience of the user so their contents can be copied to known hosts files. These files are created using ssh-keygen(1).

/etc/openssh/ssh_known_hosts

Systemwide list of known host keys. This file should be prepared by the system administrator to contain the public host keys of all machines in the organization. The format of this file is described above. This file should be writable only by root/the owner and should be world-readable.

/etc/openssh/sshd_config

Contains configuration data for sshd. The file format and configuration options are described in sshd_config(5).

/etc/openssh/sshrc

Similar to ~/.ssh/rc, it can be used to specify machine-specific login-time initializations globally. This file should be writable only by root, and should be world-readable.

/var/empty

chroot(2) directory used by sshd during privilege separation in the pre-authentication phase. The directory should not contain any files and must be owned by root and not group or world-writable.

/var/run/sshd.pid

Contains the process ID of the sshd listening for connections (if there are several daemons running concurrently for different ports, this contains the process ID of the one started last). The content of this file is not sensitive; it can be world-readable.

## SEE ALSO
scp(1), sftp(1), ssh(1), ssh-add(1), ssh-agent(1), ssh-keygen(1), ssh-keyscan(1), chroot(2), moduli(5), sshd_config(5), inetd(8), sftp-server(8)

## 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 versions 1.5 and 2.0. Niels Provos and Markus Friedl contributed support for privilege separation.


openvas

package: openvas-scanner

title: openvas(8)

text:
# openvas(8)

## NAME
openvas - The Scanner of the Greenbone Vulnerability Management

## SYNOPSIS
openvas [-V] [-h] [-c config-file] [--scan-start scan-uuid] [-u] [-s] [-y]

## DESCRIPTION
Greenbone Vulnerability Management (GVM) is a vulnerability auditing and management framework made up of several modules. The OpenVAS Scanner, openvas is in charge of executing many security tests against many target hosts in a highly optimized way.

openvas inspects the remote hosts to list all the vulnerabilities and common misconfigurations that affects them.

It is a command line tool with parameters to update the feed of vulnerability tests and to start a scan. The second part of the interface is the redis store where the parameters about a scan task need to be placed and from where the results can be retrieved.

## OPTIONS
-c <config-file>, --config-file=<config-file>

Use the alternate configuration file instead of /etc/openvas/openvas.conf

-V, --version

Prints the version number and exits

-h, --help

Show a summary of the commands

--scan-start=<scan-uuid>

ID for a single scan task. The scanner will start the scan with the data already loaded in a redis KB, which will be found using the given scan-id.

--scan-stop=<scan-uuid>

ID for a single scan task. The scanner will search the redis kb associated to the given scan_id. It takes the pid from the kb and sends the SIGUSR1 kill signal to stop the scan.

-u, --update-vt-info

Updates VT info into redis store from VT files.

## THE CONFIGURATION FILE
The default openvas configuration file, /etc/openvas/openvas.conf contains these options:

plugins_folder

Contains the location of the plugins folder. This is usually /var/lib/openvas/plugins, but you may change this.

include_folders

Contains the location of the include file folder. This is usually /var/lib/openvas/plugins, but you may change this.

max_hosts

is maximum number of hosts to test at the same time which should be given to the client (which can override it). This value must be computed given your bandwidth, the number of hosts you want to test, your amount of memory and the horsepower of your processor(s).

max_checks

is the number of plugins that will run against each host being tested. Note that the total number of process will be max_checks x max_hosts so you need to find a balance between these two options. Note that launching too many plugins at the same time may disable the remote host, either temporarily (ie: inetd closes its ports) or definitely (the remote host crash because it is asked to do too many things at the same time), so be careful.

log_whole_attack

If this option is set to 'yes', openvas will store the name, pid, date and target of each plugin launched. This is helpful for monitoring and debugging purpose, however this option might make openvas fill your disk rather quickly.

db_address

Path to the redis socket where the plugins cache and knowledge bases are stored.

report_scripts

Stores in a file the script run duration in json format. This option expects a valid path to store a file with scripts stats. Script run durations are collected only if the log_whole_attack setting is set to 'yes'. This is helpful for monitoring and debugging purpose, however this option might make openvas fill your disk rather quickly.

debug_tls

This is an scanner-only option which allows you to set the TLS log level. The level is an integer between 0 and 9. Higher values mean more verbosity and might make openvas fill your disk rather quickly. The default value is 0 (disabled). Larger values should only be used with care, since they may reveal sensitive information in the scanner logs.

Use a debug level over 10 to enable all debugging options.

log_plugins_name_at_load

If this option is set to 'yes', openvas will log the name of each plugin being loaded at startup, or each time it receives the HUP signal.

cgi_path

By default, openvas looks for default CGIs in /cgi-bin and /scripts. You may change these to something else to reflect the policy of your site. The syntax of this option is the same as the shell $PATH variable: path1:path2:...

port_range

This is the default range of ports that the scanner plugins will probe. The syntax of this option is flexible, it can be a single range ("1-1500"), several ports ("21,23,80"), several ranges of ports ("1-1500,32000-33000"). Note that you can specify UDP and TCP ports by prefixing each range by T or U. For instance, the following range will make openvas scan UDP ports 1 to 1024 and TCP ports 1 to 65535 : "T:1-65535,U:1-1024".

test_alive_hosts_only

If this option is set to 'yes', openvas will scan the target list for alive hosts in a separate process while only testing those hosts which are identified as alive. This boosts the scan speed of target ranges with a high amount of dead hosts significantly.

alive_test_ports

Preference to set the port list for the TCP SYN and TCP ACK alive test methods. This setting overwrites the default port list: "21-23,25,53,80,110-111,135,139,143,443,445,993,995,1723,3306,3389,5900,8080".

test_alive_wait_timeout

This option is to set how long (in sec) Boreas (alive test) waits for replies after last packet was sent. Default: 3 seconds.

icmp_retries

This is the default amount of icmp packets that will be sent to the host target during an alive test. Defaults to 1.

icmp_grace_period

Wait time between icmp packets during alive tests. Useful for sensitive targets. It can slow down the alive test.

optimize_test

By default, optimize_test is enabled which means openvas does trust the remote host banners and is only launching plugins against the services they have been designed to check. For example it will check a web server claiming to be IIS only for IIS related flaws but will skip plugins testing for Apache flaws, and so on. This default behavior is used to optimize the scanning performance and to avoid false positives. If you are not sure that the banners of the remote host have been tampered with, you can disable this option.

optimization_level

Level of test optimization. It checks if plugins requirement are met. Level=1 checks only that required ports are open, level=2 checks open ports and keys requirements are met, else checks also if excluded keys are present or not. Default: no optimization, check everything.

test_empty_vhost

If set to yes, the scanner will also test the target by using empty vhost value in addition to the target's associated vhost values.

checks_read_timeout

Number of seconds that the security checks will wait for when doing a recv(). You should increase this value if you are running openvas across a slow network link (testing a host via a dialup connection for instance).

timeout_retry

Number of retries when a socket connection attempt timesout.

open_sock_max_attempts

When a port is found as opened at the beginning of the scan, and for some reason the status changes to filtered/closed, it will not be possible to open a socket. This is the number of unsuccessful retries to open the socket before to set the port as closed. This avoids to launch plugins which need the opened port as a mandatory key, therefore it avoids an overlong scan duration. If the set value is 0 or a negative value, this option is disabled. It should be take in account that one unsuccessful attempt needs the number of retries set in "timeout_retry".

time_between_request

Some devices do not appreciate quick connection establishment and termination neither quick request. This option allows you to set a wait time between two actions like to open a tcp socket, to send a request through the open tcp socket, and to close the tcp socket. This value should be given in milliseconds. If the set value is 0 (default value), this option is disabled and there is no wait time between requests.

expand_vhosts

Whether to expand the target host's list of vhosts with values gathered from sources such as reverse-lookup queries and VT checks for SSL/TLS certificates.

non_simult_ports

Some services (in particular SMB) do not appreciate multiple connections at the same time coming from the same host. This option allows you to prevent openvas to make two connections on the same given ports at the same time. The syntax of this option is "port1[, port2....]". Note that you can use the KB notation of openvas to designate a service formally. Ex: "139, Services/www", will prevent openvas from making two connections at the same time on port 139 and on every port which hosts a web server.

allow_simultaneous_ips

If set to no, this option prevent openvas to scan more than one different IPs (e.g. the IPv4 and IPv6 addresses) which belong to the same host at the same time. Default, yes.

plugins_timeout

This is the maximum lifetime, in seconds of a plugin. It may happen that some plugins are slow because of the way they are written or the way the remote server behaves. This option allows you to make sure your scan is never caught in an endless loop because of a non-finishing plugin. Doesn't affect ACT_SCANNER plugins.

scanner_plugins_timeout

Like plugins_timeout, but for ACT_SCANNER plugins.

max_vts_timeouts

During a scan it might happen that a host unexpectedly shuts down, a firewall blocks the traffic, a network device issue break the connection, etc. This leads to many NVT timeouts and long scan durations. This option checks the alive status of the host again after the provided amount of max NVT timeouts are reached. If the host is considered dead the scan will be stopped for this host. Otherwise the scan will continue. This option requires Boreas alive test to be enabled. Default: option not set, disabled.

safe_checks

Most of the time, openvas attempts to reproduce an exceptional condition to determine if the remote services are vulnerable to certain flaws. This includes the reproduction of buffer overflows or format strings, which may make the remote server crash. If you set this option to 'yes', openvas will disable the plugins which have the potential to crash the remote services, and will at the same time make several checks rely on the banner of the service tested instead of its behavior towards a certain input. This reduces false positives and makes openvas nicer towards your network, however this may make you miss important vulnerabilities (as a vulnerability affecting a given service may also affect another one).

auto_enable_dependencies

OpenVAS plugins use the result of each other to execute their job. For instance, a plugin which logs into the remote SMB registry will need the results of the plugin which finds the SMB name of the remote host and the results of the plugin which attempts to log into the remote host. If you want to only select a subset of the plugins available, tracking the dependencies can quickly become tiresome. If you set this option to 'yes', openvas will automatically enable the plugins that are depended on.

hosts_allow

Comma-separated list of the only targets that are authorized to be scanned. Supports the same syntax as the list targets. Both target hostnames and the address to which they resolve are checked. Hostnames in hosts_allow list are not resolved however.

hosts_deny

Comma-separated list of targets that are not authorized to be scanned. Supports the same syntax as the list targets. Both target hostnames and the address to which they resolve are checked. Hostnames in hosts_deny list are not resolved however.

sys_hosts_allow

Like hosts_allow. Can't be overridden by the client.

sys_hosts_deny

Like hosts_deny. Can't be overridden by the client.

max_sysload

Maximum load on the system. Once this load is reached, no further VTs are started until the load drops below this value again.

min_free_mem

Minimum available memory (in MB) which should be kept free on the system. Once this limit is reached, no further VTs are started until sufficient memory is available again.

max_mem_kb

Maximum amount of memory (in MB) allowed to use for a single script. If this value is set, the amount of memory put into redis is tracked for every Script. If the amount of memory exceeds this limit, the script is not able to set more kb items. The tracked the value written into redis is only estimated, as it does not check, if a value was replaced or appended. The size of the key is also not tracked. If this value is not set or <= 0, the maximum amount is unlimited (Default).

unscanned_closed

This defines whether TCP ports that were not scanned should be treated like closed ports. Defaults to "yes".

unscanned_closed_udp

This defines whether UDP ports that were not scanned should be treated as closed ports. Defaults to "yes".

table_driven_lsc

This option will enable table driven local security Checks (LSC). This means gathered packages are sent to a specialized scanner. This is far more efficient than doing checks via NASL. Defaults to true.

mqtt_server_uri

URI to the MQTT server used for internal communication with Notus (table driven LSC). This implementation of Notus is in python and it is deprecated, being replaced with a Rust implementation of Notus.

mqtt_user

Username for authenticated MQTT communication.

mqtt_pass

Password for authenticated MQTT communication.

openvasd_server

Openvasd server URI to Rust implementation of Notus. It has priority over MQTT settings.

x-apikey

API Key for authenticate against openvasd when Notus Rust implementation is enabled.

nasl_no_signature_check

Enable/disable the Feed signacture check. Pay attention to the negative logic of this setting. The other options in this file can usually be redefined by the client.

## NETWORK USAGE
Bear in mind that OpenVAS can be quite network intensive. Even if the OpenVAS developers have taken every effort to avoid packet loss (including transparently resending UDP packets, waiting for data to be received in TCP connections, etc.) so bandwidth use should always be closely monitored, with current server hardware, bandwidth is usually the bottleneck in a OpenVAS scan. It might not became too apparent in the final reports, scanners will still run, holes might be detected, but you will risk to run into false negatives (i.e. OpenVAS will not report a security hole that is present in a remote host)

Users might need to tune OpenVAS configuration if running the scanner in low bandwidth conditions (low being 'less bandwidth that the one your hardware system can produce) or otherwise will get erratic results. There are several parameters that can be modified to reduce network load:

checks_read_timeout

The default value is set to 5 seconds, that can (should) be increased if network bandwidth is low in the openvas.conf or openvasrc configuration files. Notice that it is recommended to increase this this value, if you are running a test outside your LAN (i.e. to Internet hosts through an Internet connection), to over 10 seconds.

max_hosts

Number of hosts to test at the same time. It can be as low as you want it to be (obviously 1 is the minimum)

max_checks

Number of checks to test at the same time it can be as low as you want it to be and it will also reduce network load and improve performance (obviously 1 is the minimum) Notice that OpenVAS will spawn max_hosts * max_checks processes.

drop_privileges

If this preference is set to 'yes', OpenVAS will attempt to drop its root privilege before launching any VT and the new process owner is 'nobody'; the default value of this preference is 'no', meaning no change in behaviour.

nasl_drop_privileges_user

If a user is set, NASL functions can use this user to drop its root privilege. The new process owner is set only for those process calling a nasl function which supports a drop privileges action. This preference must not be mixed with 'drop_privileges'. If 'drop_privileges' is enabled, this option should not be used, as 'drop_privileges' sets the owner to

vendor_version

Use the alternate vendor instead of the default one during scans. Other options might be using the QoS features offered by your server operating system or your network to improve the bandwidth use.

It is not easy to give a bandwidth estimate for a OpenVAS run, you will probably need to make your own counts. However, assuming you test 65536 TCP ports. This will require at least a single packet per port that is at least 40 bytes large. Add 14 bytes for the ethernet header and you will send 65536 * (40 + 14) = 3670016 bytes. So for just probing all TCP ports we may need a multitude of this as nmap will try to resend the packets twice if no response is received.

A very rough estimate is that a full scan for UDP, TCP and RPC as well as all NASL scripts may result in 8 to 32 MB worth of traffic per scanned host. Reducing the amount of tested part and such will reduce the amount of data to be transferred significantly.

## SEE ALSO
gvmd(8), gsad(8), ospd-openvas(8), openvas-nasl(1), openvas-nasl-lint(1),

## MORE INFORMATION
The canonical places where you will find more information about OpenVAS are:

Community Portal

Development Platform

Traditional home site

## AUTHORS
openvas was forked from nessusd in 2005. Nessusd was written by Renaud Deraison <deraison@cvs.nessus.org>. Most new code since 2005 developed by Greenbone AG.