Linux Serial Consoles for Servers and Clusters. Managing Many Servers from a Console Server Serial consoles always have been a standard feature of enterprise UNIX hardware. Modern high-density server and cluster configurations sometimes can squeeze more than 50 servers in a 19' rack, so having monitors and keyboards for each one is unthinkable.
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Using a serial console on Linux is much like using a modem; the technology is virtually identical, but instead of using a modem to dial into a remote system, a special serial cable, called a null-modem cable, is strung between two computers via their serial ports. Most modern desktops and laptops no longer come with serial ports; however, virtually all server-class systems do.
The one system is set up to listen on one end of the cable, and the other system is used to log in, as the client, on the other end. This can be reverted very easily; a null-modem cable works both ways. Why use a serial console? For one, it can be very useful for debugging, particularly if the network is down and the system is headless. For another, you can use it to bypass security rules and bridge one network to another -- not for things like copying files, but purely for login purposes to obtain shell access to the other system. For instance, if you had a server in a DMZ, you could bypass potentially complex networking needs to obtain shell access to the server from a system on the LAN. This also could mean that running a remotely-accessible sshd service is no longer required on the DMZ server.
To begin, all you really need is the null-modem cable and two systems with serial ports, making sure the serial ports are enabled in the BIOS. On the server, edit /etc/inittab and add:
This tells init to launch agetty, listening on /dev/ttyS0 (the first serial port) at a baud-rate of 115200bps, and to use vt102 terminal emulation. On the client, once the null-modem cable is in place and agetty is running, use screen to connect:
Hit enter once screen starts and you will be sitting at a familiar login prompt on the remote system. Download pes 17 patch for pc. To disconnect, simply type [CTRL-A]+K in screen, after logging out.
If you were so inclined, you could also force syslog to send all logs to the serial port as well, for observation over the serial line. This can be done by modifying /etc/syslog.conf to add:
If nothing else, should you need to connect to some hardware via the console, like a network router or switch, being able to use screen to manage the serial connection is a great and easy way to do so. Virtually all Linux distributions either come with screen preinstalled, or it's a simple apt-get, urpmi, or yum away. Most Linux distributions come with agetty already installed.
Linux Serial Console Setup
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The Serial Console in the Azure portal provides access to a text-based console for Linux virtual machines (VMs) and virtual machine scale set instances. This serial connection connects to the ttys0 serial port of the VM or virtual machine scale set instance, providing access to it independent of the network or operating system state. The serial console can only be accessed by using the Azure portal and is allowed only for those users who have an access role of Contributor or higher to the VM or virtual machine scale set.
Serial Console works in the same manner for VMs and virtual machine scale set instances. In this doc, all mentions to VMs will implicitly include virtual machine scale set instances unless otherwise stated.
For Serial Console documentation for Windows, see Serial Console for Windows.
Note
Linux Serial Console Speed
The Serial Console is generally available in global Azure regions. It is not yet available in Azure government or Azure China clouds.
Prerequisites
Note
The serial console requires a local user with a configured password. VMs or virtual machine scale sets configured only with an SSH public key won't be able to sign in to the serial console. To create a local user with a password, use the VMAccess Extension, which is available in the portal by selecting Reset password in the Azure portal, and create a local user with a password.You can also reset the administrator password in your account by using GRUB to boot into single user mode.
Serial Console Linux distribution availability
For the serial console to function properly, the guest operating system must be configured to read and write console messages to the serial port. Most Endorsed Azure Linux distributions have the serial console configured by default. Selecting Serial console in the Support + troubleshooting section of the Azure portal provides access to the serial console.
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Note
If you are not seeing anything in the serial console, make sure that boot diagnostics is enabled on your VM. Hitting Enter will often fix issues where nothing is showing up in the serial console.
Custom Linux images
To enable the serial console for your custom Linux VM image, enable console access in the file /etc/inittab to run a terminal on
ttyS0 . For example: S0:12345:respawn:/sbin/agetty -L 115200 console vt102 . You may also need to spawn a getty on ttyS0. This can be done with systemctl start [email protected] .
You will also want to add ttys0 as the destination for serial output. For more information on configuring a custom image to work with the serial console, see the general system requirements at Create and upload a Linux VHD in Azure.
If you're building a custom kernel, consider enabling these kernel flags:
CONFIG_SERIAL_8250=y and CONFIG_MAGIC_SYSRQ_SERIAL=y . The configuration file is typically located in the /boot/ path.
Common scenarios for accessing the Serial Console
Disable the Serial Console
By default, all subscriptions have serial console access enabled. You can disable the serial console at either the subscription level or VM/virtual machine scale set level. For detailed instructions, visit Enable and disable the Azure Serial Console.
Serial console securityAccess securityLinux Serial Console Screen
Access to the serial console is limited to users who have an access role of Virtual Machine Contributor or higher to the virtual machine. If your Azure Active Directory tenant requires multi-factor authentication (MFA), then access to the serial console will also need MFA because the serial console's access is through the Azure portal.
Channel security
All data that is sent back and forth is encrypted on the wire.
Audit logs
All access to the serial console is currently logged in the boot diagnostics logs of the virtual machine. Access to these logs are owned and controlled by the Azure virtual machine administrator.
Caution
No access passwords for the console are logged. However, if commands run within the console contain or output passwords, secrets, user names, or any other form of personally identifiable information (PII), those will be written to the VM boot diagnostics logs. They will be written along with all other visible text, as part of the implementation of the serial console's scroll back function. These logs are circular and only individuals with read permissions to the diagnostics storage account have access to them. However, we recommend following the best practice of using the Remote Desktop for anything that may involve secrets and/or PII.
Concurrent usage
If a user is connected to the serial console and another user successfully requests access to that same virtual machine, the first user will be disconnected and the second user connected to the same session.
Caution
This means that a user who's disconnected won't be logged out. The ability to enforce a logout upon disconnect (by using SIGHUP or similar mechanism) is still on the roadmap. For Windows there is an automatic timeout enabled in Special Administrative Console (SAC); however, for Linux you can configure the terminal timeout setting. To do so, add
export TMOUT=600 in your .bash_profile or .profile file for the user you use to sign in to the console. This setting will time out the session after 10 minutes.
Accessibility
Accessibility is a key focus for the Azure Serial Console. To that end, we've ensured that the serial console is fully accessible.
Keyboard navigationLinux Serial Console Azure
Use the Tab key on your keyboard to navigate in the serial console interface from the Azure portal. Your location will be highlighted on screen. To leave the focus of the serial console window, press Ctrl+F6 on your keyboard.
Use Serial Console with a screen reader
The serial console has screen reader support built in. Navigating around with a screen reader turned on will allow the alt text for the currently selected button to be read aloud by the screen reader.
Known issues
We're aware of some issues with the serial console and the VM's operating system. Here's a list of these issues and steps for mitigation for Linux VMs. These issues and mitigations apply for both VMs and virtual machine scale set instances. If these don't match the error you're seeing, see the common serial console service errors at Common Serial Console errors.
Frequently asked questions
Q. How can I send feedback?
A. Provide feedback by creating a GitHub issue at https://aka.ms/serialconsolefeedback. Alternatively (less preferred), you can send feedback via [email protected] or in the virtual machine category of https://feedback.azure.com.
Q. Does the serial console support copy/paste?
A. Yes. Use Ctrl+Shift+C and Ctrl+Shift+V to copy and paste into the terminal.
Q. Can I use serial console instead of an SSH connection?
A. While this usage may seem technically possible, the serial console is intended to be used primarily as a troubleshooting tool in situations where connectivity via SSH isn't possible. We recommend against using the serial console as an SSH replacement for the following reasons:
Q. Who can enable or disable serial console for my subscription?
A. To enable or disable the serial console at a subscription-wide level, you must have write permissions to the subscription. Roles that have write permission include administrator or owner roles. Custom roles can also have write permissions.
Q. Who can access the serial console for my VM/virtual machine scale set?
A. You must have the Virtual Machine Contributor role or higher for a VM or virtual machine scale set to access the serial console.
Q. My serial console isn't displaying anything, what do I do?
A. Your image is likely misconfigured for serial console access. For information about configuring your image to enable the serial console, see Serial console Linux distribution availability.
Q. Is the serial console available for virtual machine scale sets?
Linux Serial Console Program
A. Yes, it is! See Serial Console for Virtual Machine Scale Sets
Q. If I set up my VM or virtual machine scale set by using only SSH key authentication, can I still use the serial console to connect to my VM/virtual machine scale set instance?
A. Yes. Because the serial console doesn't require SSH keys, you only need to set up a username/password combination. You can do so by selecting Reset password in the Azure portal and using those credentials to sign in to the serial console.
Linux Serial Console GuiNext stepsLinux Serial Console Login
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