Difference between revisions of "OpenSSH"
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− | '''[[wikipedia:OpenSSH|OpenSSH]]''' is a popular suite of software utilities implementing [[Secure Shell]] (SSH) protocol. OpenSSH includes the ability to set up a [[TCP]] secured channel and it is widely use as a replacement for not secured [[telnet]] and secure replacement of file transfers such as rcp and ftp. OpenSSH offers a great number of features including ssh session multiplexing. | + | '''[[wikipedia:OpenSSH|OpenSSH]]''' is a popular suite of software utilities implementing [[Secure Shell]] (SSH) protocol. OpenSSH includes the ability to set up a [[TCP]] secured channel and it is widely use as a replacement for not secured [[telnet]] and secure replacement of file transfers such as rcp and ftp. OpenSSH offers a great number of features including ssh [[session multiplexing]]. |
<ref>https://en.wikibooks.org/wiki/OpenSSH/Cookbook/Multiplexing</ref><ref>https://stackoverflow.com/questions/20410252/how-to-reuse-an-ssh-connection</ref> | <ref>https://en.wikibooks.org/wiki/OpenSSH/Cookbook/Multiplexing</ref><ref>https://stackoverflow.com/questions/20410252/how-to-reuse-an-ssh-connection</ref> | ||
The OpenSSH suite includes the following command-line utilities and daemons: | The OpenSSH suite includes the following command-line utilities and daemons: | ||
− | * <code>[[ssh (OpenSSH client)|ssh]]</code>, ssh client and TCP secure replacement for | + | * <code>[[ssh (OpenSSH client)|ssh]]</code>, [[ssh client]] and TCP secure replacement for <code>[[rlogin]]</code>, <code>[[rsh]]</code> and <code>[[telnet]]</code> to allow shell access to a remote machine. |
* <code>[[scp]]</code>, a replacement for <code>[[rcp]]</code> | * <code>[[scp]]</code>, a replacement for <code>[[rcp]]</code> | ||
* <code>sftp</code>, a replacement for <code>[[ftp]]</code> to copy files between computers | * <code>sftp</code>, a replacement for <code>[[ftp]]</code> to copy files between computers | ||
* <code>[[sshd]]</code>, the SSH server daemon which allows shell access and file transfers to a remote machine. | * <code>[[sshd]]</code>, the SSH server daemon which allows shell access and file transfers to a remote machine. | ||
* <code>[[ssh-keygen]]</code>, a tool to inspect and generate the RSA, DSA and Elliptic Curve keys that are used for user and host authentication | * <code>[[ssh-keygen]]</code>, a tool to inspect and generate the RSA, DSA and Elliptic Curve keys that are used for user and host authentication | ||
+ | * <code>[[ssh-keyscan]]</code>, which scans a list of hosts and collects their public keys | ||
* <code>[[ssh-agent]]</code> and <code>[[ssh-add]]</code>, utilities to ease authentication by holding keys ready and avoid the need to enter passphrases every time they are used | * <code>[[ssh-agent]]</code> and <code>[[ssh-add]]</code>, utilities to ease authentication by holding keys ready and avoid the need to enter passphrases every time they are used | ||
− | |||
* <code>[[ssh-copy-id]]</code>, copy local keys to remote machine. | * <code>[[ssh-copy-id]]</code>, copy local keys to remote machine. | ||
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* [[Wikibooks: OpenSSH]] | * [[Wikibooks: OpenSSH]] | ||
* [[OpenSSH changelog]] | * [[OpenSSH changelog]] | ||
+ | |||
+ | == Config == | ||
+ | * Client: <code>[[/etc/ssh/ssh_config]]</code> or <code>~./[[config]]</code> | ||
+ | * Server: <code>[[/etc/ssh/sshd_config]]</code> | ||
== ssh clients == | == ssh clients == | ||
− | OpenSSH includes an ssh client:<code>[[ssh]]</code>. Others clients are available such us <code> | + | OpenSSH includes an ssh client:<code>[[ssh]]</code>. Others clients are available such us <code>[[PuTTY]]</code>, <code>mosh</code>, <code>paramiko</code> and <code>autossh</code><ref>https://linux.die.net/man/1/autossh</ref>. |
<code>autossh</code><ref>https://linux.die.net/man/1/autossh</ref> main feature not include in OpenSSH ssh client is the capability to monitor an ssh connection and restart it if necessary. | <code>autossh</code><ref>https://linux.die.net/man/1/autossh</ref> main feature not include in OpenSSH ssh client is the capability to monitor an ssh connection and restart it if necessary. | ||
− | * Loop waiting to connect to server: <code>AUTOSSH_POLL=5 AUTOSSH_GATETIME=0 autossh -M 0 -o ServerAliveInterval=5 -o ServerAliveCountMax=1 YOUR_SERVER_NAME_OR_IP</code> | + | * Loop waiting to connect to server: <code>AUTOSSH_POLL=5 AUTOSSH_GATETIME=0 [[autossh]] -M 0 -o ServerAliveInterval=5 -o ServerAliveCountMax=1 YOUR_SERVER_NAME_OR_IP</code> |
Ssh clients in Linux are frequently executed inside a terminal or using any kind of terminal multiplexer such as <code>[[tmux]]</code> or <code>[[screen]]</code>. | Ssh clients in Linux are frequently executed inside a terminal or using any kind of terminal multiplexer such as <code>[[tmux]]</code> or <code>[[screen]]</code>. | ||
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== Activities == | == Activities == | ||
=== Basic === | === Basic === | ||
− | * ''Convert a | + | * Install OpenSSH: <code>[[apt install]] openssh-server</code> |
+ | * ''Convert a [[PuTTY]] ssh key format to Openssh format'', you can follow the following instructions http://www.codeblocq.com/2016/05/Convert-a-putty-ppk-key-to-a-pem-file-on-OSX/, https://stackoverflow.com/questions/3475069/use-ppk-file-in-mac-terminal-to-connect-to-remote-connection-over-ssh | ||
* Open a reverse ssh tunnel, follow the following instructions https://www.howtoforge.com/reverse-ssh-tunneling | * Open a reverse ssh tunnel, follow the following instructions https://www.howtoforge.com/reverse-ssh-tunneling | ||
* [[Configure OpenSSH to reuse ssh connections]] (<code>ControlMaster</code>) | * [[Configure OpenSSH to reuse ssh connections]] (<code>ControlMaster</code>) | ||
* Generate a public Key from a private Key: <ref>https://serverfault.com/questions/52285/create-a-public-ssh-key-from-the-private-key</ref><code>[[ssh-keygen]] -f ~/.ssh/id_rsa -y > ~/.ssh/id_rsa.pub</code> (example for [[RSA]] keys but can be applied to other key types) | * Generate a public Key from a private Key: <ref>https://serverfault.com/questions/52285/create-a-public-ssh-key-from-the-private-key</ref><code>[[ssh-keygen]] -f ~/.ssh/id_rsa -y > ~/.ssh/id_rsa.pub</code> (example for [[RSA]] keys but can be applied to other key types) | ||
* [[Configure OpenSSH to allow Public-key authentication]] (<code>authorized_keys</code>)<ref>https://www.digitalocean.com/community/tutorials/how-to-configure-ssh-key-based-authentication-on-a-linux-server</ref> | * [[Configure OpenSSH to allow Public-key authentication]] (<code>authorized_keys</code>)<ref>https://www.digitalocean.com/community/tutorials/how-to-configure-ssh-key-based-authentication-on-a-linux-server</ref> | ||
− | * [[ | + | * [[Activate SSH on macOS]]: <code>sudo [[systemsetup]] -setremotelogin on</code> |
− | * Activate [[ | + | * [[Activate OpenSSH on Windows]] ([[Windows Server 2019]] or [[Windows 10]]):<ref>https://docs.microsoft.com/en-us/windows-server/administration/openssh/openssh_install_firstuse</ref> |
− | |||
− | |||
− | |||
− | |||
=== Intermediate === | === Intermediate === | ||
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=== Advanced === | === Advanced === | ||
# Read ssh documentation about multiplexing https://en.wikibooks.org/wiki/OpenSSH/Cookbook/Multiplexing and its implementation details: http://cvsweb.openbsd.org/cgi-bin/cvsweb/src/usr.bin/ssh/PROTOCOL.mux?annotate=HEAD | # Read ssh documentation about multiplexing https://en.wikibooks.org/wiki/OpenSSH/Cookbook/Multiplexing and its implementation details: http://cvsweb.openbsd.org/cgi-bin/cvsweb/src/usr.bin/ssh/PROTOCOL.mux?annotate=HEAD | ||
− | # Configure ssh session multiplexing | + | # Configure ssh session [[multiplexing]] |
# Use <code>[[ProxyJump]]</code> directive to connect using a "Jump Server"<ref>https://en.wikibooks.org/wiki/OpenSSH/Cookbook/Proxies_and_Jump_Hosts#Passing_Through_One_or_More_Gateways_Using_ProxyJump</ref> | # Use <code>[[ProxyJump]]</code> directive to connect using a "Jump Server"<ref>https://en.wikibooks.org/wiki/OpenSSH/Cookbook/Proxies_and_Jump_Hosts#Passing_Through_One_or_More_Gateways_Using_ProxyJump</ref> | ||
# Run a shell script on a remote machine using ssh: <code>ssh root@MachineB 'bash -s' < local_script.sh</code><ref>https://stackoverflow.com/a/2732991</ref>. See also: [[parallel]] | # Run a shell script on a remote machine using ssh: <code>ssh root@MachineB 'bash -s' < local_script.sh</code><ref>https://stackoverflow.com/a/2732991</ref>. See also: [[parallel]] | ||
# Read https://github.com/openssh/openssh-portable source code | # Read https://github.com/openssh/openssh-portable source code | ||
# Read [[OpenSSH changelog]] | # Read [[OpenSSH changelog]] | ||
+ | |||
+ | == Related terms == | ||
+ | * [[MAC (message authentication code)]] | ||
+ | * [[Damien Miller]] | ||
+ | * [[Key Revocation Lists (KRL)]] | ||
+ | * [[AWS EC2 Instance Connect]] (Jun 2019) | ||
== See also == | == See also == |
Latest revision as of 13:13, 20 October 2022
OpenSSH is a popular suite of software utilities implementing Secure Shell (SSH) protocol. OpenSSH includes the ability to set up a TCP secured channel and it is widely use as a replacement for not secured telnet and secure replacement of file transfers such as rcp and ftp. OpenSSH offers a great number of features including ssh session multiplexing. [1][2]
The OpenSSH suite includes the following command-line utilities and daemons:
ssh
, ssh client and TCP secure replacement forrlogin
,rsh
andtelnet
to allow shell access to a remote machine.scp
, a replacement forrcp
sftp
, a replacement forftp
to copy files between computerssshd
, the SSH server daemon which allows shell access and file transfers to a remote machine.ssh-keygen
, a tool to inspect and generate the RSA, DSA and Elliptic Curve keys that are used for user and host authenticationssh-keyscan
, which scans a list of hosts and collects their public keysssh-agent
andssh-add
, utilities to ease authentication by holding keys ready and avoid the need to enter passphrases every time they are usedssh-copy-id
, copy local keys to remote machine.
Contents
Readings[edit]
Config[edit]
- Client:
/etc/ssh/ssh_config
or~./config
- Server:
/etc/ssh/sshd_config
ssh clients[edit]
OpenSSH includes an ssh client:ssh
. Others clients are available such us PuTTY
, mosh
, paramiko
and autossh
[3].
autossh
[4] main feature not include in OpenSSH ssh client is the capability to monitor an ssh connection and restart it if necessary.
- Loop waiting to connect to server:
AUTOSSH_POLL=5 AUTOSSH_GATETIME=0 autossh -M 0 -o ServerAliveInterval=5 -o ServerAliveCountMax=1 YOUR_SERVER_NAME_OR_IP
Ssh clients in Linux are frequently executed inside a terminal or using any kind of terminal multiplexer such as tmux
or screen
.
Activities[edit]
Basic[edit]
- Install OpenSSH:
apt install openssh-server
- Convert a PuTTY ssh key format to Openssh format, you can follow the following instructions http://www.codeblocq.com/2016/05/Convert-a-putty-ppk-key-to-a-pem-file-on-OSX/, https://stackoverflow.com/questions/3475069/use-ppk-file-in-mac-terminal-to-connect-to-remote-connection-over-ssh
- Open a reverse ssh tunnel, follow the following instructions https://www.howtoforge.com/reverse-ssh-tunneling
- Configure OpenSSH to reuse ssh connections (
ControlMaster
) - Generate a public Key from a private Key: [5]
ssh-keygen -f ~/.ssh/id_rsa -y > ~/.ssh/id_rsa.pub
(example for RSA keys but can be applied to other key types) - Configure OpenSSH to allow Public-key authentication (
authorized_keys
)[6] - Activate SSH on macOS:
sudo systemsetup -setremotelogin on
- Activate OpenSSH on Windows (Windows Server 2019 or Windows 10):[7]
Intermediate[edit]
- Learn about different client connection options, such us:
-oBatchMode=yes
or-o ConnectTimeout=2
[8] - Connect to remote server temporarily turning off host key checking, (security implications):
ssh -oStrictHostKeyChecking=no SERVER_NAME
Advanced[edit]
- Read ssh documentation about multiplexing https://en.wikibooks.org/wiki/OpenSSH/Cookbook/Multiplexing and its implementation details: http://cvsweb.openbsd.org/cgi-bin/cvsweb/src/usr.bin/ssh/PROTOCOL.mux?annotate=HEAD
- Configure ssh session multiplexing
- Use
ProxyJump
directive to connect using a "Jump Server"[9] - Run a shell script on a remote machine using ssh:
ssh root@MachineB 'bash -s' < local_script.sh
[10]. See also: parallel - Read https://github.com/openssh/openssh-portable source code
- Read OpenSSH changelog
Related terms[edit]
- MAC (message authentication code)
- Damien Miller
- Key Revocation Lists (KRL)
- AWS EC2 Instance Connect (Jun 2019)
See also[edit]
- Telnet (deprecated use), netcat
- OpenSSH (changelog):
/etc/ssh/sshd_config
|/etc/ssh/ssh_config
|~/.ssh/
|openSSL | sshd logs
|sftp
|scp
|authorized_keys
|ssh-keygen
|ssh-keyscan
|ssh-add
|ssh-agent
|ssh
|Ssh -O stop
|ssh-copy-id
|CheckHostIP
|UseKeychain
, OpenSSF sslh
[11] Applicative Protocol Multiplexer (e.g. share SSH and HTTPS on the same port)sshpass
(brew install http://git.io/sshpass.rb
)conch
client written in python- openssl
- Port knocking,
fail2ban
[12]fwknop
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Original source: https://en.wikiversity.org/wiki/OpenSSH
- ↑ https://en.wikibooks.org/wiki/OpenSSH/Cookbook/Multiplexing
- ↑ https://stackoverflow.com/questions/20410252/how-to-reuse-an-ssh-connection
- ↑ https://linux.die.net/man/1/autossh
- ↑ https://linux.die.net/man/1/autossh
- ↑ https://serverfault.com/questions/52285/create-a-public-ssh-key-from-the-private-key
- ↑ https://www.digitalocean.com/community/tutorials/how-to-configure-ssh-key-based-authentication-on-a-linux-server
- ↑ https://docs.microsoft.com/en-us/windows-server/administration/openssh/openssh_install_firstuse
- ↑ https://linux.die.net/man/1/ssh
- ↑ https://en.wikibooks.org/wiki/OpenSSH/Cookbook/Proxies_and_Jump_Hosts#Passing_Through_One_or_More_Gateways_Using_ProxyJump
- ↑ https://stackoverflow.com/a/2732991
- ↑ https://github.com/yrutschle/sslh
- ↑ https://serverfault.com/a/608976
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