Where is ssh config file ubuntu

Multiple ciphers must be comma-separated. The default is: aesctr,aesctr,aesctr,arcfour,arcfour, aesgcm openssh. ClearAllForwardings Specifies that all local, remote, and dynamic port forwardings specified in the configuration files or on the command line be cleared. This option is primarily useful when used from the ssh 1 command line to clear port forwardings set in configuration files, and is automatically set by scp 1 and sftp 1.

Compression Specifies whether to use compression. CompressionLevel Specifies the compression level to use if compression is enabled. The argument must be an integer from 1 fast to 9 slow, best. The default level is 6, which is good for most applications. The meaning of the values is the same as in gzip 1. Note that this option applies to protocol version 1 only. ConnectionAttempts Specifies the number of tries one per second to make before exiting. The argument must be an integer.

This may be useful in scripts if the connection sometimes fails. The default is 1. This value is used only when the target is down or really unreachable, not when it refuses the connection. ControlMaster Enables the sharing of multiple sessions over a single network connection.

These sessions will try to reuse the master instance's network connection rather than initiating new ones, but will fall back to connecting normally if the control socket does not exist, or is not listening. If the ControlPath cannot be opened, ssh will continue without connecting to a master instance. X11 and ssh-agent 1 forwarding is supported over these multiplexed connections, however the display and agent forwarded will be the one belonging to the master connection i.

Two additional options allow for opportunistic multiplexing: try to use a master connection but fall back to creating a new one if one does not already exist.

This ensures that shared connections are uniquely identified. ControlPersist When used in conjunction with ControlMaster , specifies that the master connection should remain open in the background waiting for future client connections after the initial client connection has been closed.

DynamicForward Specifies that a TCP port on the local machine be forwarded over the secure channel, and the application protocol is then used to determine where to connect to from the remote machine. IPv6 addresses can be specified by enclosing addresses in square brackets. By default, the local port is bound in accordance with the GatewayPorts setting.

Multiple forwardings may be specified, and additional forwardings can be given on the command line. Only the superuser can forward privileged ports. This option should be placed in the non-hostspecific section. See ssh-keysign 8 for more information. The escape character can also be set on the command line. ExitOnForwardFailure Specifies whether ssh 1 should terminate the connection if it cannot set up all requested dynamic, tunnel, local, and remote port forwardings.

ForwardAgent Specifies whether the connection to the authentication agent if any will be forwarded to the remote machine. Agent forwarding should be enabled with caution. Users with the ability to bypass file permissions on the remote host for the agent's Unix-domain socket can access the local agent through the forwarded connection.

An attacker cannot obtain key material from the agent, however they can perform operations on the keys that enable them to authenticate using the identities loaded into the agent.

X11 forwarding should be enabled with caution. Users with the ability to bypass file permissions on the remote host for the user's X11 authorization database can access the local X11 display through the forwarded connection.

An attacker may then be able to perform activities such as keystroke monitoring if the ForwardX11Trusted option is also enabled. X11 connections received by ssh 1 after this time will be refused.

The default is to disable untrusted X11 forwarding after twenty minutes has elapsed. Furthermore, the xauth 1 token used for the session will be set to expire after 20 minutes. Remote clients will be refused access after this time. GatewayPorts Specifies whether remote hosts are allowed to connect to local forwarded ports. By default, ssh 1 binds local port forwardings to the loopback address.

This prevents other remote hosts from connecting to forwarded ports. GatewayPorts can be used to specify that ssh should bind local port forwardings to the wildcard address, thus allowing remote hosts to connect to forwarded ports. GlobalKnownHostsFile Specifies one or more files to use for the global host key database, separated by whitespace. Note that this option applies to protocol version 2 only.

The default is unset, which means that the default identity will be used. The default is unset, which means that the expected GSSAPI server identity will be determined from the target hostname. With a compatible server, this can delegate the renewed credentials to a session on the server. These hashed names may be used normally by ssh 1 and sshd 8 , but they do not reveal identifying information should the file's contents be disclosed. Note that existing names and addresses in known hosts files will not be converted automatically, but may be manually hashed using ssh-keygen 1.

HostbasedAuthentication Specifies whether to try rhosts based authentication with public key authentication. HostKeyAlgorithms Specifies the protocol version 2 host key algorithms that the client wants to use in order of preference. The default for this option is: ecdsa-sha2-nistpcert-v01 openssh. HostKeyAlias Specifies an alias that should be used instead of the real host name when looking up or saving the host key in the host key database files.

This option is useful for tunneling SSH connections or for multiple servers running on a single host. HostName Specifies the real host name to log into. This can be used to specify nicknames or abbreviations for hosts. The default is the name given on the command line. Numeric IP addresses are also permitted both on the command line and in HostName specifications. That way, the root user cannot be invoked remotely, and security will be significantly improved. If you have decided to change the default port number, you must configure your firewall to allow traffic via the specified port.

The default firewall configurations tool in Ubuntu is UFW , configure it with the command:. If you used the default port 22 , then it is not necessary to put the port number.

By following the simple steps above, you now know how to enable SSH on Ubuntu Now you can establish a reliable and secure protocol between you and a remote device.

Introduction When establishing a remote connection between a client and a server, a primary concern is ensuring security. By following the steps below, you will learn how to enable SSH on Ubuntu Was this article helpful? Sofija Simic.

Alongside her educational background in teaching and writing, she has had a lifelong passion for information technology. She is committed to unscrambling confusing IT concepts and streamlining intricate software installations. Next you should read. Security SysAdmin.

Employees sometimes do this to be able to work from home even when company policy does not permit it. Hackers use it to leave permanent backdoor. See the page on SSH tunneling for more information. Public authentication is used for passwordless logins between systems. It is often used for automated processes, such as backups, configuration management, and file transfers.

It is also used by sophisticated end users and system administrators for single sign-on. See the public key authentication for configuring it. When a user has created more than one SSH key for authentication, the -i command line option may be helpful for specifying which key to use. In the client configuration file, this can be specified using the IdentityFile options.

OpenSSH certificates can be used for authentication either using ssh-agent or by specifying the CertificateFile option in the client configuration file.

See SSH certificates for more information. Arguments may be enclosed in double quotes " in order to specify arguments that contain spaces. The following keywords can be used in SSH client configuration files. Keywords are case-insensitive and arguments are case-sensitive. Any algorithm or method names that include an at sign are for experimental use only and not recommended for production.

Restricts the following declarations to be only for those hosts that match one of the patterns given after the keyword. The pattern is matched against the host name given on the command line. Restricts the following declarations to apply only for hosts that match the specified criteria.

For detailed information, see SSH man page. Specifies which address family to use when connecting. Valid arguments are: any , inet , inet6. This is useful for running the ssh client from shell script that do not have an interactive user, and prevents accidentally blocking on a password prompt.

Specifies to use the specified address on the local machine as the source address of the connection. Specifies whether to use challenge-response authentication.

This is mostly a legacy method and has been replaced by KbdInteractiveAuthentication. Specifies the cipher to use for encrypting the session in protocol version 1. Note that use of protocol 1 is not recommended. Specifies the ciphers allowed for protocol version 2 in order of preference. Multiple ciphers must be comma-separated. The ssh -Q cipher command can be used to query supported ciphers. The following list is supported in OpenSSH 6. Specifies that all local, remote, and dynamic port forwardings specified in the configuration files or on the command line be cleared.